131. Barrio, IC; Ehrich, D; Soininen, EM; Ravolainen, VT; Bueno, CG; Gilg, O; Koltz, AM; Speed, JDM; Hik, DS; Mörsdorf, M; Alatalo, JM; Angerbjörn, A; Bêty, J; Bollache, L; Boulanger-Lapointe, N; Brown, GS; Eischeid, I; Giroux, MA; Hájek, T; Hansen, BB; Hofhuis, SP; Lamarre, J-F; Lang, J; Latty, C; Lecomte, N; Macek, P; McKinnon, L; Myers-Smith, IH; Pedersen, ÅØ; Prevéy, JS; Roth, JD; Saalfeld, ST; Schmidt, NM; Smith, P; Sokolov, A; Sokolova, N; Stolz, C; van Bemmelen, R; Varpe, Ø; Woodard, PF; Jónsdóttir IS. (2021) Developing common protocols to measure tundra herbivory across spatial scales.Arctic ScienceDeveloping common protocols to measure tundra herbivory across spatial scales
Tundra, Arctic, herbivory
Understanding and predicting large-scale ecological responses to global environmental change requires comparative studies across geographic scales with coordinated efforts and standardized methodologies. We designed, applied, and assessed standardized protocols to measure tundra herbivory at three spatial scales: plot, site (habitat), and study area (landscape). The plot- and site-level protocols were tested in the field during summers 2014–2015 at 11 sites, nine of them consisting of warming experimental plots included in the International Tundra Experiment (ITEX). The study area protocols were assessed during 2014–2018 at 24 study areas across the Arctic. Our protocols provide comparable and easy to implement methods for assessing the intensity of invertebrate herbivory within ITEX plots and for characterizing vertebrate herbivore communities at larger spatial scales. We discuss methodological constraints and make recommendations for how these protocols can be used and how sampling effort can be optimized to obtain comparable estimates of herbivory, both at ITEX sites and at large landscape scales. The application of these protocols across the tundra biome will allow characterizing and comparing herbivore communities across tundra sites and at ecologically relevant spatial scales, providing an important step towards a better understanding of tundra ecosystem responses to large-scale environmental change.Link DOI
130. Bates, AE; Primack, RB; PAN Environment Working Group; Hik, DS; Kroesen, L; Duarte, CM. (2021) Global COVID-19 lockdown highlights humans as both threats and custodians of the environment.Biological ConservationGlobal COVID-19 lockdown highlights humans as both threats and custodians of the environment
Pandemic, biodiversity, restoration, global monitoring
The global lockdown to mitigate COVID-19 pandemic health risks has altered human interactions with nature. Here, we report immediate impacts of changes in human activities on wildlife and environmental threats during the early lockdown months of 2020, based on 877 qualitative reports and 332 quantitative assessments from 89 different studies. Hundreds of reports of unusual species observations from around the world suggest that ani
mals quickly responded to the reductions in human presence. However, negative effects of lockdown on servation also emerged, as confinement resulted in some park officials being unable to perform conservation, restoration and enforcement tasks, resulting in local increases in illegal activities such as hunting. Overall, there is a complex mixture of positive and negative effects of the pandemic lockdown on nature, all of which have the potential to lead to cascading responses which in turn impact wildlife and nature conservation. While the net effect of the lockdown will need to be assessed over years as data becomes available and persistent effects emerge, immediate responses were detected across the world. Thus, initial qualitative and quantitative data arising from this serendipitous global quasi-experimental perturbation highlights the dual role that humans play in threatening and protecting species and ecosystems. Pathways to favorably tilt this delicate balance include reducing impacts and increasing conservation effectiveness.Link DOI
129. Dokis-Jansen, K; Parlee, BL; Łutsël K’e Dene First Nation; Hik, DS; Gendreau-Berthiaume, B; Macdonald, E; Stinn, C. (2021) “These trees have stories to tell”: Linking Denésƍliné oral history of caribou use with trample scar frequency on black spruce roots at Ɂedacho Kué.Arctic 74:290-305 “These trees have stories to tell”: Linking Denésƍliné oral history of caribou use with trample scar frequency on black spruce roots at Ɂedacho Kué
caribou; Rangifer; sub-Arctic; Indigenous knowledge; Dënesǫ́łıné; Łutsël K’e; dendroecology; Northwest Territories; place-based research; collaborative community-based research
For thousands of years Ɂedacho Kué (Artillery Lake, Northwest Territories) has been a key water crossing site for barren-ground caribou (Rangifer tarandus groenlandicus). Human disturbance of barren-ground caribou habitat in northern Canada has emerged as an important focus of study in the last decade; particularly in the Bathurst range of the Northwest Territories where caribou populations have declined by more than 95% since the 1980s. Guided by local Indigenous leaders and Elders, a collaborative research project was developed with the Dënesǫ́łıné people of Łutsël K’e Dëne First Nation (2012 – 14). This paper describes linkages between knowledge derived from Dënesǫ́łıné oral history and quantitative dendroecological analysis of trample scars on black spruce (Picea mariana) root samples collected at Ɂedacho Kué to provide a better understanding of caribou use at this location. Findings from oral histories and dendroecology analysis were consistent with one another and with previous dendroecology study in the region, although some discrepancies were detected in data from 1995 – 2006 that require further study to elucidate. Key findings include relatively low caribou use at Ɂedacho Kué during the 1930s and late 1960s, with use increasing into the 1970s and peaking in the late 1980s, as well as Elder and hunter reports of no caribou in some years between 2005 and 2012. This work addresses a gap in scientific data about barren-ground caribou movements at Ɂedacho Kué prior to satellite collar use in 1996 and corroborates previously documented oral histories about the enduring value of Ɂedacho Kué as critical habitat to barren-ground caribou. Given the drastic decline of the Bathurst caribou over the last two decades, more research is needed to understand movements and their relationship to population dynamics. In this context, the research approach described in this paper could be used as an example of how to meaningfully bring together place-based Indigenous knowledge and science in addressing an urgent issue of Arctic sustainability.Link DOI
128. McKnight, EA; Swanson, H; Brahney, J; Hik, DS. (2021) The physical and chemical limnology of Yukon’s largest lake, Lhù’ààn Mân’ (Kluane Lake), prior to the 2016 ‘A’ą̈y Chù’ diversion.Arctic ScienceThe physical and chemical limnology of Yukon’s largest lake, Lhù’ààn Mân’ (Kluane Lake), prior to the 2016 ‘A’ą̈y Chù’ diversion
Limnology, Yukon Climate Change, Lhu'aan Man' (Kluane Lake); 'A'ay Chu' (Slims River); physical limnology; climate change; large northern lakes
Despite increasing evidence that large northern lakes are rapidly changing due to climate change, descriptive baseline studies of their physicochemical properties are largely lacking, limiting our ability to detect or predict change. This study represents a comprehensive scientific assessment of the limnology of Yukon’s largest lake: Lhù’ààn Mân’ (Kluane Lake), an important waterbody for local and First Nation communities, and key habitat for trout and salmon. Water sample and instrument data generated throughout 2015 describe distinct regions within the lake and their respective seasonal variability. A deep, glacially-influenced southern basin was characterized by cold, turbid, poorly stratified, unproductive, and nutrient-poor conditions; a shallower northwestern region (Tthe Kaala Daagur (Brooks/Little Arm)) was warmer, fully mixed, and more productive; a northeast region (’Ùha K’ènji (Talbot/Big Arm)) was clear and stratified with intermediate depth, temperature, productivity, and nutrient concentrations; and a central region had intermediate physicochemical conditions relative to the other three. This variability demonstrates the need for adequate spatial (within lake) and temporal (between seasons) monitoring of large northern lakes. In 2016, glacier recession within the watershed resulted in diversion of the lake’s primary inflow (‘A’ą̈y Chù’ (Slims River)). Our results, when used together with Indigenous knowledge, form a historical reference that enables assessments of the potential ecological consequences to Lhù’ààn Mân’.Link DOI
127. Mulloy, TA; Barrio, IC; Jonsdottir, IS; Hik, DS. (2021) The effects of different management interventions on degraded rangelands in Iceland.Land Degrad. Dev. 32: 4583-4594 The effects of different management interventions on degraded rangelands in Iceland
fertilization; grazing exclusion; highlands; land degradation; nutrient co-limitation
Loss of vegetation and soil erosion are symptoms of widespread rangeland degradation across most of the Icelandic highlands. Areas at different stages of degradation coexist as a mosaic that includes both vegetated heathlands, and exposed gravelly deserts. Revegetation efforts have included fertilizer applications and grazing exclusion to increase plant biomass and reduce bare ground, but their effectiveness is predicted to differ depending on the stage of degradation for a certain area. In this study, we used a 4-year field experiment to test the predictions of a state-and-transition model for the Icelandic highlands. We measured the combined effects of grazing exclusion and factorial applications of nitrogen (N), phosphorus (P), and potassium (K) fertilizers, on plant biomass, species richness, amount of exposed bare ground and plant community composition in a dwarf-shrub heathland and a gravelly desert habitat. After 4 years: (1) grazing exclusion alone had no effect in either habitat; (2) fertilizers increased biomass in both habitats, especially in plots treated with NP or NK; (3) the combination of fertilizers and grazing exclusion produced the greatest amount of aboveground biomass, predominantly of forb and graminoid species. In the dwarf-shrub heath, the increase in biomass in fertilized and fenced plots also corresponded to a loss in species richness, whereas in the gravelly desert, increased biomass reduced the amount of bare ground without reducing species richness. Our results reinforce the importance in understanding the effects of different management interventions across ecological conditions to determine the most effective revegetation approach. DOI
126. Brachmann, CG; Hernandez-Ramirez, G; Hik, DS. (2020) CH4 uptake along a successional gradient in temperate alpine soils.Biogeochemistry 147: 109-123 CH4 uptake along a successional gradient in temperate alpine soils
Columbia mountains; Methane; Soil fluxes; Alpine; Deglaciated terrain, treelike
The effects of climate change appear to be amplified in mountains compared with lowland areas, with rapid changes in plant community composition, soil properties, and increased substrate for biological development following retreat of glaciers. Associated soil gaseous fluxes in alpine ecosystems contribute to the global balance of greenhouse gases, but methane and carbon dioxide soil fluxes and their controls are not well known. We used a dynamic closed-chamber method to measure methane and carbon dioxide fluxes along a successional gradient during the peak growing season in the North Selkirk Mountains, British Columbia, Canada. Soil physico-chemical properties, vegetation cover, and topographic variables were quantified to determine mechanisms influencing these fluxes. Mean methane uptake ranged from - 155 mu g CH4-C m(- 2) h(-1) in well vegetated sites to zero in recently deglaciated terrain. Soil total carbon (TC) and water content were the primary drivers of methane uptake. Sites with TC greater than 4% and moisture below 0.22 water fraction by volume (w.f.v) corresponded to the strongest methane sinks. Increased vegetation cover and relatively drier soil conditions, anticipated with future climate change, suggest that methane uptake may increase in these alpine ecosystems. DOI
125. Deakin, S; Gorrell, JC; Kneteman, J; Hik, DS; Jobin, RM; Coltman, DW. (2020) Spatial genetic structure of Rocky Mountain bighorn sheep (Ovis canadensis canadensis) at the northern limit of their native range.Can. J. Zool. 98: 317-330 Spatial genetic structure of Rocky Mountain bighorn sheep (Ovis canadensis canadensis) at the northern limit of their native range
spatial genetic structure; post-glacial recolonization; ungulates; terrestrial; alpine; Rocky Mountain bighorn sheep; Ovis canadensis canadensis
The Canadian Rocky Mountains are one of the few places on Earth where the spatial genetic structure of wide-ranging species has been relatively unaffected by anthropogenic disturbance. We characterized the spatial genetic structure of Rocky Mountain bighorn sheep (Ovis canadensis canadensis Shaw, 1804) in the northern portion of their range. Using microsatellites from 1495 individuals and mitochondrial DNA sequences from 188 individuals, we examined both broad- and fine-scale spatial genetic structure, assessed sex-biased gene flow within the northern portion of the species range, and identified geographic patterns of genetic diversity. We found that broad-scale spatial genetic structure was consistent with barriers to movement created by major river valleys. The fine-scale spatial genetic structure was characterized by a strong isolation-by-distance pattern, and analysis of neighborhood size using spatial autocorrelation indicated gene flow frequently occurred over distances of up to 100 km. However, analysis of sex-specific spatial autocorrelation and analysis of mitochondrial haplotype distributions failed to detect any evidence of sex-biased gene flow. Finally, our analyses reveal decreasing genetic diversity with increasing latitude, consistent with patterns of post-glacial recolonization of the Rocky Mountains. DOI
124. Kroesen, LP; Hik, DS; Cherry, SG. (2020) Patterns of decadal, seasonal and daily visitation to mineral licks, a critical resource hotspot for mountain goats Oreamnos americanus in the Rocky Mountains.Wildlife Biol. 2020 Patterns of decadal, seasonal and daily visitation to mineral licks, a critical resource hotspot for mountain goats Oreamnos americanus in the Rocky Mountains
hotspot; mineral lick; mountain goats; Oreamnos americanus; sex-specific patterns; temporal patterns
Concentrated resources or hotspots, within an individual's usual home range may be strong determinates of movement behavior. We evaluated the patterns of mineral lick use by a population of mountain goats Oreamnos americanus displaying high site fidelity at two mineral licks along the Trans-Canada Highway in the Rocky Mountains, British Columbia, Canada. Access to these mineral licks was characterized by deliberate and repetitive movements into marginal habitat. We describe the patterns of mineral lick use over decadal, seasonal and daily periods by using dendrochronological analysis of trampling scars along mountain goat trails, movements determined from GPS collar locations, and camera traps placed along trails and at mineral licks, respectively. Our findings suggest that mountain goats have strong trans-generational behavioral traditions and that they predictably access mineral licks using the same trails, seasons and daily patterns. Differences in the patterns of mineral lick visitation between males and females may be related to reproductive and nutritional status, while their nocturnal use appears to be a response to disturbance at the mineral licks. Understanding how animals adjust their behavior in response to highly localized resource hotspots outside their usual home range can provide valuable information for the management of these critical habitat features and the wider conservation of mountain goat populations. DOI
123. Leanne L. Chai, Guillermo Hernandez-Ramirez,⁎, David S. Hik, Isabel C. Barrio, Carol M. Frost, Cristina Chinchilla Soto, Germain Esquivel-Hernández. (2020) A methane sink in the Central American high elevation páramo: Topographic, soil moisture and vegetation effects.Geoderma 362:114092 A methane sink in the Central American high elevation páramo: Topographic, soil moisture and vegetation effects
Methane, Greenhouse gas flux, Alpine, Páramo
Methane (CH4) is a strong greenhouse gas with a global warming potential 23 times larger than that of carbon dioxide. Characterizing ecosystems as either sources or sinks for methane and their magnitudes informs on biosphere contributions to the global CH4 budget and to warming of the atmosphere. We quantified methane fluxes for the first time in a neotropical alpine páramo (Valle de Los Conejos, Chirripó Massif, Costa Rica) and examined the relationships of these fluxes with topography, soil moisture and vegetation, during the transition from dry to rainy season. Using closed chambers and laser spectroscopy, we measured soil CH4 and CO2 fluxes across a field site encompassing: a grassy plain as well as a plain, a gentle slope and a plateau dominated by a dwarf bamboo (Chusquea subtessellata Hitchcock). We found that the páramo landscape acts as a sink for CH4 [−53.1 ± 29.6 (mean ± SE) μg C m−2 hr−1]. Of the four field areas, the grassy plain was on average the strongest CH4 sink, likely because this soil profile had no drainage restrictions and was well aerated. By contrast, in the slope and plateau, a heavily-consolidated subsurface layer was shown to perch water, increasing surface soil moisture and limiting CH4 uptake. Conversely, in certain parts of the plain, where Chusquea grew vigorously in discrete, tall patches, we found intense CH4 uptake beneath these patches. Within the Chusquea plain, these hot spots of CH4 uptake localized under the tall Chusquea had double the uptake rates than outside these patches,
with even greater uptake than the average in the grassy plain. Our results show that CH4 uptake in the páramo is driven by moisture interacting with impeding soil layers, vegetation and topography.Website DOI
122. Williamson, SN; Zdanowicz, C; Anslow, FS; Clarke, GKC; Copland, L; Danby, RK; Flowers, GE; Holdsworth, G; Jarosch, AH; Hik, DS. (2020) Evidence for Elevation-Dependent Warming in the St. Elias Mountains, Yukon, Canada.J. Clim. 33: 3253-3269 Evidence for Elevation-Dependent Warming in the St. Elias Mountains, Yukon, Canada
The climate of high midlatitude mountains appears to be warming faster than the global average, but evidence for such elevation-dependent warming (EDW) at higher latitudes is presently scarce. Here, we use a comprehensive network of remote meteorological stations, proximal radiosonde measurements, downscaled temperature reanalysis, ice cores, and climate indices to investigate the manifestation and possible drivers of EDW in the St. Elias Mountains in subarctic Yukon, Canada. Linear trend analysis of comprehensively validated annual downscaled North American Regional Reanalysis (NARR) gridded surface air temperatures for the years 1979-2016 indicates a warming rate of 0.028 degrees C a(-1) between 5500 and 6000 m above mean sea level (MSL), which is similar to 1.6 times larger than the global-average warming rate between 1970 and 2015. The warming rate between 5500 and 6000 m MSL was similar to 1.5 times greater than the rate at the 2000-2500 m MSL bin (0.019 degrees C a(-1)), which is similar to the majority of warming rates estimated worldwide over similar elevation gradients. Accelerated warming since 1979, measured by radiosondes, indicates a maximum rate at 400 hPa (similar to 7010 m MSL). EDW in the St. Elias region therefore appears to be driven by recent warming of the free troposphere. MODIS satellite data show no evidence for an enhanced snow albedo feedback above 2500 m MSL, and declining trends in sulfate aerosols deposited in high-elevation ice cores suggest a modest increase in radiative forcing at these elevations. In contrast, increasing trends in water vapor mixing ratio at the 500-hPa level measured by radiosonde suggest that a longwave radiation vapor feedback is contributing to EDW. DOI
121. Barrio IC, Hik DS. (2019) Herbivory in Arctic Ecosystems.Encyclopedia of the World's Biomes 1-11 Herbivory in Arctic Ecosystems
Arctic, herbivory, tundra, climate change
Plant-herbivore interactions are a key driver of ecosystem dynamics in arctic regions. Herbivores can influence plants, plant communities and ecosystem processes, but to which extent they do so and in which direction depends on a complex set of environmental factors. Plant-herbivore interactions in arctic environments occur under particular environmental conditions, characterized by marked seasonality, short growing seasons, low temperatures and low primary productivity. These conditions limit the ability of tundra plants to respond to herbivory and imply that herbivores require specific adaptations to cope with the highly heterogeneous plant production. Here, we provide an overview of arctic herbivores and their
influences on plants, vegetation, and ecosystem processes in arctic environments, and how these interactions are likely to be altered by the rapid environmental changes happening in this region. We review current efforts and methods used to study plant-herbivore interactions in the Arctic, including recent developments related to invertebrate herbivory and managed
grazing systems. Herbivory is an active topic of research in arctic environments given the potential of herbivores to counteract some of the changes associated with recent environmental changes. The field is moving forward, and the increased coordination of research efforts will allow generating more robust predictions of the consequences of the rapid
ongoing environmental changes in this region. DOI
119. Rheubottom, SI; Barrio, IC; Kozlov, MV; Alatalo, JM; Andersson, T; Asmus, AL; Baubin, C; Brearley, FQ; Egelkraut, DD; Ehrich, D; Gauthier, G; Jonsdottir, IS; Konieczka, S; Levesque, E; Olofsson, J; Prevey, JS; Slevan-Tremblay, G; Sokolov, A; Sokolova, N; Sokovnina, S; Speed, JDM; Suominen, O; Zverev, V; Hik, DS. (2019) Hiding in the background: community-level patterns in invertebrate herbivory across the tundra biome.Polar Biol. 42: 1881-1897 Hiding in the background: community-level patterns in invertebrate herbivory across the tundra biome
Background herbivory; Biomass loss; Climate change; Community-weighted average; Invertebrate; Insects; Tundra
Invertebrate herbivores depend on external temperature for growth and metabolism. Continued warming in tundra ecosystems is proposed to result in increased invertebrate herbivory. However, empirical data about how current levels of invertebrate herbivory vary across the Arctic is limited and generally restricted to a single host plant or a small group of species, so predicting future change remains challenging. We investigated large-scale patterns of invertebrate herbivory across the tundra biome at the community level and explored how these patterns are related to long-term climatic conditions and year-of-sampling weather, habitat characteristics, and aboveground biomass production. Utilizing a standardized protocol, we collected samples from 92 plots nested within 20 tundra sites during summer 2015. We estimated the community-weighted biomass lost based on the total leaf area consumed by invertebrates for the most common plant species within each plot. Overall, invertebrate herbivory was prevalent at low intensities across the tundra, with estimates averaging 0.94% and ranging between 0.02 and 5.69% of plant biomass. Our results suggest that mid-summer temperature influences the intensity of invertebrate herbivory at the community level, consistent with the hypothesis that climate warming should increase plant losses to invertebrates in the tundra. However, most of the observed variation in herbivory was associated with other site level characteristics, indicating that other local ecological factors also play an important role. More details about the local drivers of invertebrate herbivory are necessary to predict the consequences for rapidly changing tundra ecosystems. DOI
118. Tara A Mulloy, Isabel C Barrio, Katrín Björnsdóttir, Ingibjörg Svala Jónsdóttir, David S Hik. (2019) Fertilisers mediate the short-term effects of sheep grazing in the Icelandic highlands.Icelandic Agricultural Science 32:75-85 Fertilisers mediate the short-term effects of sheep grazing in the Icelandic highlands
fertiliser application, soil erosion, sheep grazing, subarctic rangelands.
Sustainable grazing management in tundra ecosystems is receiving increasing attention. In the Icelandic highlands, past grazing practices have played a major role in the extensive soil erosion, leaving many parts of this tundra rangeland in poor condition. However, the impacts of current grazing practices are not well understood. We measured the short-term effect of grazing by comparing the amount of bare ground and aboveground biomass in grazed and ungrazed plots, with and without fertiliser application, in adjacent dwarfshrub heaths and sparsely vegetated areas, at two sites within and outside the volcanic active zone. Grazing
did not affect the amount of bare ground, but in the fertilised plots grazing consistently reduced plant biomass (mainly graminoids). Fertiliser application can increase grazing intensity, which can counteract the additional biomass accumulation. Consequently, the removal of biomass by sheep needs to be considered when fertilisers are used as part of a strategy to combat erosion.PDF DOI
117. Tiusanen, M; Huotari, T; Hebert, PDN; Andersson, T; Asmus, A; Bety, J; Davis, E; Gale, J; Hardwick, B; Hik, D; Korner, C; Lanctot, RB; Loonen, MJJE; Partanen, R; Reischke, K; Saalfeld, ST; Senez-Gagnon, F; Smith, PA; Sulavik, J; Syvanpera, I; Urbanowicz, C; Williams, S; Woodard, P; Zaika, Y; Roslin, T. (2019) Flower-visitor communities of an arcto-alpine plant-Global patterns in species richness, phylogenetic diversity and ecological functioning.Mol. Ecol. 28 Flower-visitor communities of an arcto-alpine plant-Global patterns in species richness, phylogenetic diversity and ecological functioning
arctic ecology; DNA barcoding; Dryas; ecosystem functioning; flower visitor; pollination
Pollination is an ecosystem function of global importance. Yet, who visits the flower of specific plants, how the composition of these visitors varies in space and time and how such variation translates into pollination services are hard to establish. The use of DNA barcodes allows us to address ecological patterns involving thousands of taxa that are difficult to identify. To clarify the regional variation in the visitor community of a widespread flower resource, we compared the composition of the arthropod community visiting species in the genus Dryas (mountain avens, family Rosaceae), throughout Arctic and high-alpine areas. At each of 15 sites, we sampled Dryas visitors with 100 sticky flower mimics and identified specimens to Barcode Index Numbers (BINs) using a partial sequence of the mitochondrial COI gene. As a measure of ecosystem functioning, we quantified variation in the seed set of Dryas. To test for an association between phylogenetic and functional diversity, we characterized the structure of local visitor communities with both taxonomic and phylogenetic descriptors. In total, we detected 1,360 different BINs, dominated by Diptera and Hymenoptera. The richness of visitors at each site appeared to be driven by local temperature and precipitation. Phylogeographic structure seemed reflective of geological history and mirrored trans-Arctic patterns detected in plants. Seed set success varied widely among sites, with little variation attributable to pollinator species richness. This pattern suggests idiosyncratic associations, with function dominated by few and potentially different taxa at each site. Taken together, our findings illustrate the role of post-glacial history in the assembly of flower-visitor communities in the Arctic and offer insights for understanding how diversity translates into ecosystem functioning. DOI PubMed
116. Barrio, IC; Hik, DS; Thorsson, J; Svavarsdottir, K; Marteinsdottir, B; Jonsdottir, IS. (2018) The sheep in wolf's clothing? Recognizing threats for land degradation in Iceland using state-and-transition models.Land Degrad. Dev. 29: 1714-1725 The sheep in wolf's clothing? Recognizing threats for land degradation in Iceland using state-and-transition models
adaptive monitoring; land management; rangeland; sheep grazing
Land degradation and extensive soil erosion are serious environmental concerns in Iceland. Natural processes associated with a harsh climate and frequent volcanic activity have shaped Icelandic landscapes. However, following human settlement and the introduction of livestock in the ninth century, the extent of soil erosion rapidly escalated. Despite increased restoration and afforestation efforts and a considerable reduction in sheep numbers during the late 20th century, many Icelandic rangelands remain in poor condition. A deeper understanding of the ecology of these dynamic landscapes is needed, and state-and-transition models (STMs) can provide a useful conceptual framework. STMs have been developed for ecosystems worldwide to guide research, monitoring, and management but have been used at relatively small spatial scales and have not been extensively applied to high-latitude rangelands. Integrating the best available knowledge, we develop STMs for rangelands in Iceland, where sheep grazing is often regarded as a main driver of degradation. We use STMs at a countrywide scale for 3 time periods with different historical human influence, from presettlement to present days. We also apply our general STM to a case-study in the central highlands of Iceland to illustrate the potential application of these models at scales relevant to management. Our STMs identify the set of possible states, transitions and thresholds in these ecosystems, and their changes over time and suggest increasing complexity in recent times. This approach can help identify important knowledge gaps and inform management efforts and monitoring programmes, by identifying realistic and achievable conservation and restoration goals. DOI
115. Barrio, IC; Linden, E; Beest, M; Olofsson, J; Rocha, A; Soininen, EM; Alatalo, JM; Andersson, T; Asmus, A; Boike, J; Brathen, KA; Bryant, JP; Buchwal, A; Bueno, CG; Christie, KS; Denisova, YV; Egelkraut, D; Ehrich, D; Fishback, L; Forbes, BC; Gartzia, M; Grogan, P; Hallinger, M; Heijmans, MMPD; Hik, DS; Hofgaard, A; Holmgren, M; Hoye, TT; Huebner, DC; Jonsdottir, IS; Kaarlejarvi, E; Kumpula, T; Lange, CYMJG; Lange, J; Levesque, E; Limpens, J; Macias-Fauria, M; Myers-Smith, I; Nieukerken, EJ; Normand, S; Post, ES; Schmidt, NM; Sitters, J; Skoracka, A; Sokolov, A; Sokolova, N; Speed, JDM; Street, LE; Sundqvist, MK; Suominen, O; Tananaev, N; Tremblay, JP; Urbanowicz, C; Uvarov, SA; Watts, D; Wilmking, M; Wookey, PA; Zimmermann, HH; Zverev, V; Kozlov, MV. (2018) Publisher Correction to: Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome (vol 40, pg 2265, 2017).Polar Biol. 41: 1653-1654 Publisher Correction to: Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome (vol 40, pg 2265, 2017)
The above mentioned article was originally scheduled for publication in the special issue on Ecology of Tundra Arthropods with guest editors Toke T. Hoye . Lauren E. Culler. Erroneously, the article was published in Polar Biology, Volume 40, Issue 11, November, 2017. The publisher sincerely apologizes to the guest editors and the authors for the inconvenience caused. DOI
114. Bjorkman, AD; Myers-Smith, IH; Elmendorf, SC; Normand, S; Ruger, N; Beck, PSA; Blach-Overgaard, A; Blok, D; Cornelissen, JHC; Forbes, BC; Georges, D; Goetz, SJ; Guay, KC; Henry, GHR; HilleRisLambers, J; Hollister, RD; Karger, DN; Kattge, J; Manning, P; Prevey, JS; Rixen, C; Schaepman-Strub, G; Thomas, HJD; Vellend, M; Wilmking, M; Wipf, S; Carbognani, M; Hermanutz, L; Levesque, E; Molau, U; Petraglia, A; Soudzilovskaia, NA; Spasojevic, MJ; Tomaselli, M; Vowles, T; Alatalo, JM; Alexander, HD; Anadon-Rosell, A; Angers-Blondin, S; te Beest, M; Berner, L; Bjork, RG; Buchwal, A; Buras, A; Christie, K; Cooper, EJ; Dullinger, S; Elberling, B; Eskelinen, A; Frei, ER; Grau, O; Grogan, P; Hallinger, M; Harper, KA; Heijmans, MMPD; Hudson, J; Hulber, K; Iturrate-Garcia, M; Iversen, CM; Jaroszynska, F; Johnstone, JF; Jorgensen, RH; Kaarlejarvi, E; Klady, R; Kuleza, S; Kulonen, A; Lamarque, LJ; Lantz, T; Little, CJ; Speed, JDM; Michelsen, A; Milbau, A; Nabe-Nielsen, J; Nielsen, SS; Ninot, JM; Oberbauer, SF; Olofsson, J; Onipchenko, VG; Rumpf, SB; Semenchuk, P; Shetti, R; Collier, LS; Street, LE; Suding, KN; Tape, KD; Trant, A; Treier, UA; Tremblay, JP; Tremblay, M; Venn, S; Weijers, S; Zamin, T; Boulanger-Lapointe, N; Gould, WA; Hik, DS; Hofgaard, A; Jonsdottir, IS; Jorgenson, J; Klein, J; Magnusson, B; Tweedie, C; Wookey, PA; Bahn, M; Blonder, B; van Bodegom, PM; Bond-Lamberty, B; Campetella, G; Cerabolini, BEL; Chapin, FS; Cornwell, WK; Craine, J; Dainese, M; de Vries, FT; Diaz, S; Enquist, BJ; Green, W; Milla, R; Niinemets, U; Onoda, Y; Ordonez, JC; Ozinga, WA; Penuelas, J; Poorter, H; Poschlod, P; Reich, PB; Sande, B; Schamp, B; Sheremetev, S; Weiher, E. (2018) Plant functional trait change across a warming tundra biome.Nature 562 Plant functional trait change across a warming tundra biome
The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature-trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming. DOI PubMed
113. Myers-Smith, IH; Hik, DS. (2018) Climate warming as a driver of tundra shrubline advance.J. Ecol. 106: 547-560 Climate warming as a driver of tundra shrubline advance
age distributions; alpine; climate; high-latitude; range expansion; recruitment; shrub; tundra; willow (Salix); Yukon
1. Climate warming is predicted to alter ecological boundaries in high-latitude ecosystems including the elevational or latitudinal extent of tall shrubs in Arctic and alpine tundra. Over 60 studies from 128 locations around the tundra biome have investigated shrub expansion in tundra ecosystems; however, only six studies test whether shrublines are actually advancing up hill-slopes or northward into tundra where tall shrubs are currently absent. 2. We test the hypothesis that willow shrublines have expanded to higher elevations in relation to climate across a 50 x 50 km area in the Kluane Region of the southwest Yukon Territory, Canada by surveying of 379 shrubs at 14 sites and sampling of 297 of the surveyed shrubs at 10 sites. We compared growth and recruitment to climate variables to test the climate sensitivity of shrub increase using annual radial growth analysis, age distributions and repeat field surveys to estimate the current rate of shrubline advance. 3. We found consistent and increasing rates of recruitment of alpine willows, with estimates of faster advancing shrublines on shallower hill-slopes. Mortality was extremely low across the elevation gradient. Aspect, elevation and species identity did not explain variation in recruitment patterns, suggesting a regional factor, such as climate, as the driver of the observed shrubline advance. 4. Annual radial growth of willows was best explained by variation in summer temperatures, and recruitment pulses by winter temperatures. Measured recruitment rates are similar to 20 +/- 5 individuals per hectare per decade (M +/- SE) and measured rates of increased shrub cover of similar to 5 +/- 1% per decade (M +/- SE) measured at the Pika Camp site between field surveys in 2009 and 2013. Our results suggest that shrubline will continue to advance over the next 50 years, if growing conditions remain suitable. However, if future conditions differ between summer and winter seasons, this could lead to contrasting trajectories for recruitment vs. growth, and influence the vegetation change observed on the landscape. 5. Synthesis. Our findings in the context of a review of the existing literature indicate that elevational and latitudinal shrublines, like treelines, are advancing in response to climate warming; however, the trajectories of change will depend on the climate drivers controlling recruitment vs. growth. DOI
112. Williamson, SN; Anslow, FS; Clarke, GKC; Gamon, JA; Jarosch, AH; Hik, DS. (2018) Spring warming in Yukon mountains is not amplified by the snow albedo feedback.Sci Rep 8 Spring warming in Yukon mountains is not amplified by the snow albedo feedback
alpine
Decreasing spring snow cover may amplify Arctic warming through the snow albedo feedback. To examine the impact of snowmelt on increasing temperature we used a 5,000 m elevation gradient in Yukon, Canada, extending from valley-bottom conifer forests, through middle elevation tundra, to high elevation icefields, to compare validated downscaled reanalysis air temperature patterns across elevational bands characterized by different patterns of spring snowmelt. From 2000 to 2014 we observed surface warming of 0.01 degrees C/a.1,000 m in May (0.14 degrees C/a at 1,000 m to 0.19 degrees C/a at 5,000 m), and uniform cooling of 0.09 degrees C/a in June at all elevations. May temperature trends across elevationally dependent land cover types were highly correlated with each other despite large variations in albedo and snow cover trends. Furthermore, a clear dependency of infrared skin temperature on snow cover mediated albedo decline was observed in tundra, but this was insufficient to influence average diurnal air temperature. We observed negative June temperature trends which we attribute to increasing daytime cloud cover because albedo and snow cover trends were unchanging. We conclude that 8-day and monthly averaged Spring air temperature trends are responding to a synoptic external forcing that is much stronger than the snow albedo feedback in sub-Arctic mountains. DOI
111. Barrio, IC; Linden, E; Te Beest, M; Olofsson, J; Rocha, A; Soininen, EM; Alatalo, JM; Andersson, T; Asmus, A; Boike, J; Brathen, KA; Bryant, JP; Buchwal, A; Bueno, CG; Christie, KS; Denisova, YV; Egelkraut, D; Ehrich, D; Fishback, L; Forbes, BC; Gartzia, M; Grogan, P; Hallinger, M; Heijmans, MMPD; Hik, DS; Hofgaard, A; Holmgren, M; Hoye, TT; Huebner, DC; Jonsdottir, IS; Kaarlejarvi, E; Kumpula, T; Lange, CYMJG; Lange, J; Levesque, E; Limpens, J; Macias-Fauria, M; Myers-Smith, I; van Nieukerken, EJ; Normand, S; Post, ES; Schmidt, NM; Sitters, J; Skoracka, A; Sokolov, A; Sokolova, N; Speed, JDM; Street, LE; Sundqvist, MK; Suominen, O; Tananaev, N; Tremblay, JP; Urbanowicz, C; Uvarov, SA; Watts, D; Wilmking, M; Wookey, PA; Zimmermann, HH; Zverev, V; Kozlov, MV. (2017) Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome.Polar Biol. 40: 2265-2278 Background invertebrate herbivory on dwarf birch (Betula glandulosa-nana complex) increases with temperature and precipitation across the tundra biome
Background insect herbivory; Climate change; Externally feeding defoliators; Latitudinal Herbivory Hypothesis; Leaf damage; Leaf miners; Gall makers; Macroecological pattern
Chronic, low intensity herbivory by invertebrates, termed background herbivory, has been understudied in tundra, yet its impacts are likely to increase in a warmer Arctic. The magnitude of these changes is however hard to predict as we know little about the drivers of current levels of invertebrate herbivory in tundra. We assessed the intensity of invertebrate herbivory on a common tundra plant, the dwarf birch (Betula glandulosa-nana complex), and investigated its relationship to latitude and climate across the tundra biome. Leaf damage by defoliating, mining and gall-forming invertebrates was measured in samples collected from 192 sites at 56 locations. Our results indicate that invertebrate herbivory is nearly ubiquitous across the tundra biome but occurs at low intensity. On average, invertebrates damaged 11.2% of the leaves and removed 1.4% of total leaf area. The damage was mainly caused by external leaf feeders, and most damaged leaves were only slightly affected (12% leaf area lost). Foliar damage was consistently positively correlated with mid-summer (July) temperature and, to a lesser extent, precipitation in the year of data collection, irrespective of latitude. Our models predict that, on average, foliar losses to invertebrates on dwarf birch are likely to increase by 6-7% over the current levels with a 1 degrees C increase in summer temperatures. Our results show that invertebrate herbivory on dwarf birch is small in magnitude but given its prevalence and dependence on climatic variables, background invertebrate herbivory should be included in predictions of climate change impacts on tundra ecosystems. DOI
110. McGetrick, JA; Bubela, T; Hik, DS. (2017) Automated content analysis as a tool for research and practice: a case illustration from the Prairie Creek and Nico environmental assessments in the Northwest Territories, Canada.Impact Assess. Proj. Apprais. 35: 139-147 Automated content analysis as a tool for research and practice: a case illustration from the Prairie Creek and Nico environmental assessments in the Northwest Territories, Canada
Automated content analysis; circumpolar region; environmental assessment; natural resource development; public hearings; public participation
Public engagement is essential to the procedural and substantive sustainability of environmental assessment. Public hearings present the lowest barrier to entry for public participation, but these forums face competing political pressures for conducting appropriate public engagement within an expeditious process. Repositories of public hearing testimony provide a source of primary data for examining these public engagement issues during environmental assessments. However, the time and resources required may be prohibitive for conducting the kind of in-depth qualitative analyses that are commonly used. Automated content analysis (ACA) techniques can provide a rapid, replicable, inductive, and systematic way to examine public hearing transcripts, consisting of the critical development and application of computer programming scripts that synthesize evidence from extensive document sets. This case illustration demonstrates the potential utility of ACA, based on the examination of two public hearings, Prairie Creek (EA0809-002; 2008-2011) and Nico (EA0809-004; 2009-2013) conducted in the Mackenzie Valley, Northwest Territories, Canada. Our interpretation of the findings provides an evaluation of ACA methods and situates its potential to inform environmental assessment research and practice across jurisdictions. DOI
109. Roslin, T; Hardwick, B; Novotny, V; Petry, WK; Andrew, NR; Asmus, A; Barrio, IC; Basset, Y; Boesing, AL; Bonebrake, TC; Cameron, EK; Dattilo, W; Donoso, DA; Drozd, P; Gray, CL; Hik, DS; Hill, SJ; Hopkins, T; Huang, S; Koane, B; Laird-Hopkins, B; Laukkanen, L; Lewis, OT; Milne, S; Mwesige, I; Nakamura, A; Nell, CS; Nichols, E; Prokurat, A; Sam, K; Schmidt, NM; Slade, A; Slade, V; Suchankova, A; Teder, T; van Nouhuys, S; Vandvik, V; Weissflog, A; Zhukovich, V; Slade, EM. (2017) Higher predation risk for insect prey at low latitudes and elevations.Science 356: 742-744 Higher predation risk for insect prey at low latitudes and elevations
Biotic interactions underlie ecosystem structure and function, but predicting interaction outcomes is difficult. We tested the hypothesis that biotic interaction strength increases toward the equator, using a global experiment with model caterpillars to measure predation risk. Across an 11,660-kilometer latitudinal gradient spanning six continents, we found increasing predation toward the equator, with a parallel pattern of increasing predation toward lower elevations. Patterns across both latitude and elevation were driven by arthropod predators, with no systematic trend in attack rates by birds or mammals. These matching gradients at global and regional scales suggest consistent drivers of biotic interaction strength, a finding that needs to be integrated into general theories of herbivory, community organization, and life-history evolution. DOI
108. Williamson, SN; Hik, DS; Gamon, JA; Jarosch, AH; Anslow, FS; Clarke, GKC; Rupp, TS. (2017) Spring and summer monthly MODIS LST is inherently compared to air temperature in snow covered sub-Arctic mountains.Remote Sens. Environ. 189: 14-24 Spring and summer monthly MODIS LST is inherently compared to air temperature in snow covered sub-Arctic mountains
MODIS LST; Downscaled NARR; SNAP; Snow cover; Cloud cover; Cryosphere: alpine
Satellite-derived land surface temperature (skin temperature) provides invaluable information for data-sparse high elevation and Arctic regions. However, the relationship between satellite-derived clear-sky skin temperature and various downscaled air temperature products for snow covered sub-Arctic alpine regions remain poorly understood, such that trend analysis or air temperature product integration is difficult. We compared monthly average air temperatures from two independent downscaled temperature products to MODIS Land Surface Temperature (LST) and air temperature at nine meteorological stations situated above tree-line in the southwest Yukon, Canada, between May and August 2008 for a full range of snow cover fractions. We found that both down scaled products generally agreed with LST for the low elevation, snow-free, vegetation classes. However, a systematic cold bias in Average LST emerged for snow fractions greater than approximately 40%, and this bias increased in magnitude as snow cover increased. In these situations the downscaled air temperatures were 57 degrees C warmer than Average LST for snow fractions of >90%, and this pattern was largely independent of the number of measurements of LST within a month. Maximum LST was similar to average air temperatures for high snow fractions, but Minimum LST was colder by 10 degrees C or more for all snow fractions. Consequently, the average of Maximum and Minimum LST produces the cold bias, compared to air temperature, for high snow cover fractions. Air temperature measured at nine meteorological monitoring stations located between elevations of 1408-2690 m, on land cover classes Barren, Sparsely Vegetated or Permanent Snow and Ice, confirmed the cold bias results when incorporating Minimum LST in monthly averages. For snow fractions of <40% the RMSE for all of the temperature products was <2.5 degrees C when compared to station air temperature and all biases were positive and <2.0 degrees C. For snow fractions of >40%, the average LST bias became strongly negative at -4.5 degrees C, and the RMSE increased to 6.1 degrees C, whereas the downscaled products bias and RMSE were similar to those from snow fractions of <40%. A weak warm bias for all the temperature products occurred for small snow fractions over non-forested land cover classes. Downscaled air temperature fields show physically real differences from Average LST in spring and summer, caused by snow cover and the interplay of Maximum and Minimum LST. These findings indicate that the integration of MODIS 1ST with downscaled air temperature products or local air temperature requires the incorporation of snow cover. (C) 2016 Elsevier Inc. All rights reserved. DOI
107. Barrio, IC; Bueno, CG; Gartzia, M; Soininen, EM; Christie, KS; Speed, JDM; Ravolainen, VT; Forbes, BC; Gauthier, G; Horstkotte, T; Hoset, KS; Hoye, TT; Jonsdottir, IS; Levesque, E; Morsdorf, MA; Olofsson, J; Wookey, PA; Hik, DS. (2016) Biotic interactions mediate patterns of herbivore diversity in the Arctic.Glob. Ecol. Biogeogr. 25: 1108-1118 Biotic interactions mediate patterns of herbivore diversity in the Arctic
Biodiversity; biotic interactions; predator-prey; species richness; trophic interactions; tundra
AimUnderstanding the forces shaping biodiversity patterns, particularly for groups of organisms with key functional roles, will help predict the responses of ecosystems to environmental changes. Our aim was to evaluate the relative role of different drivers in shaping the diversity patterns of vertebrate herbivores, a group of organisms exerting a strong trophic influence in terrestrial Arctic ecosystems. This biome, traditionally perceived as homogeneous and low in biodiversity, includes wide variation in biotic and physical conditions and is currently undergoing major environmental change. LocationThe Arctic (including the High Arctic, Low Arctic and Subarctic) MethodsWe compiled available data on vertebrate (birds and mammals) herbivore distribution at a pan-Arctic scale, and used eight variables that represent the most relevant hypotheses for explaining patterns of species richness. We used range maps rasterized on a 100kmx100km equal-area grid to analyse richness patterns of all vertebrate herbivore species combined, and birds and mammalian herbivores separately. ResultsOverall, patterns of herbivore species richness in the Arctic were positively related to plant productivity (measured using the normalized difference vegetation index) and to the species richness of predators. Greater species richness of herbivores was also linked to areas with a higher mean annual temperature. Species richness of avian and mammalian herbivores were related to the distance from the coast, with the highest avian richness in coastal areas and mammalian richness peaking further inland. Main conclusionsHerbivore richness in the Arctic is most strongly linked to primary productivity and the species richness of predators. Our results suggest that biotic interactions, with either higher or lower trophic levels or both, can drive patterns of species richness at a biome-wide scale. Rapid ongoing environmental changes in the Arctic are likely to affect herbivore diversity through impacts on both primary productivity and changes in predator communities via range expansion of predators from lower latitudes. DOI
106. Barrio, IC; Bueno, CG; Hik, DS. (2016) Warming the tundra: reciprocal responses of invertebrate herbivores and plants.Oikos 125: 20-28 Warming the tundra: reciprocal responses of invertebrate herbivores and plants
Rapid warming in northern ecosystems is simultaneously influencing plants, herbivores and the interactions among them. Recent studies suggest that herbivory could buffer plant responses to environmental change, but this has only been shown for vertebrate herbivores so far. The role of invertebrate herbivory in tundra ecosystems is often overlooked, but can be relevant in determining the structure and dynamics of tundra plant communities and may also affect how plants respond to warming. Invertebrate herbivores are also likely to respond more rapidly to warming than vertebrates because their behaviour and life cycles strongly depend on temperature. We investigated the effects of current season warming on Arctic moth caterpillars, their herbivory rates, and the subsequent responses of two common tundra plants, Salix arctica and Dryas octopetala. We manipulated both herbivore presence and temperature in a full-factorial field experiment at two elevations, using enclosures and passive warming chambers. Changes in temperature achieved through elevation and/or experimental warming directly affected caterpillars, herbivory and the responses of plants. Caterpillars performed worse (higher respiration rates and lower growth rates) in warmer, lower elevation plots and shifted their diets towards more nutritious foods, such that the relative intensity of herbivory changed for the two studied plants. Within-season responses of both forage plant species were weak, but invertebrate herbivores affected the responses of plants to elevation or experimental warming. Our results suggest that increased temperatures can reduce the performance of cold-adapted invertebrate herbivores, with potential consequences to the longer term responses of tundra plants to warming due to changes in herbivory rates and selective foraging. DOI
105. Barrio, IC; Hik, DS; Jonsdottir, IS; Bueno, CG; Morsdorf, MA; Ravolainen, VT. (2016) Herbivory Network: An international, collaborative effort to study herbivory in Arctic and alpine ecosystems.Polar Sci. 10: 297-302 Herbivory Network: An international, collaborative effort to study herbivory in Arctic and alpine ecosystems
Coordinated experiment; Plant-herbivore interactions; Research network; Tundra: alpine; plants
Plant-herbivore interactions are central to the functioning of tundra ecosystems, but their outcomes vary over space and time. Accurate forecasting of ecosystem responses to ongoing environmental changes requires a better understanding of the processes responsible for this heterogeneity. To effectively address this complexity at a global scale, coordinated research efforts, including multi-site comparisons within and across disciplines, are needed. The Herbivory Network was established as a forum for researchers from Arctic and alpine regions to collaboratively investigate the multifunctional role of herbivores in these changing ecosystems. One of the priorities is to integrate sites, methodologies, and metrics used in previous work, to develop a set of common protocols and design long-term geographically-balanced, coordinated experiments. The implementation of these collaborative research efforts will also improve our understanding of traditional human-managed systems that encompass significant portions of the sub-Arctic and alpine areas worldwide. A deeper understanding of the role of herbivory in these systems under ongoing environmental changes will guide appropriate adaptive strategies to preserve their natural values and related ecosystem services. (C) 2016 Elsevier B.V. and NIPR. All rights reserved. DOI
104. Bueno, CG; Williamson, SN; Barrio, IC; Helgadottir, A; Hik, DS. (2016) Moss Mediates the Influence of Shrub Species on Soil Properties and Processes in Alpine Tundra.PLoS One 11 Moss Mediates the Influence of Shrub Species on Soil Properties and Processes in Alpine Tundra
alpine plants
In tundra ecosystems, bryophytes influence soil processes directly and indirectly through interactions with overstory shrub species. We experimentally manipulated moss cover and measured seasonal soil properties and processes under two species of deciduous shrubs with contrasting canopy structures, Salix planifolia pulchra and Betula glandulosa-nana complex. Soil properties (seasonal temperature, moisture and C:N ratios) and processes (seasonal litter decomposition and soil respiration) were measured over twelve months. Shrub species identity had the largest influence on summer soil temperatures and soil respiration rates, which were higher under Salix canopies. Mosses were associated with lower soil moisture irrespective of shrub identity, but modulated the effects of shrubs on winter soil temperatures and soil C:N ratios so that moss cover reduced differences in soil winter temperatures between shrub species and reduced C:N ratios under Betula but not under Salix canopies. Our results suggest a central role of mosses in mediating soil properties and processes, with their influence depending on shrub species identity. Such species-dependent effects need to be accounted for when forecasting vegetation dynamics under ongoing environmental changes. DOI
103. Lanier H, Hik, D. (2016) Ochotona collaris.The IUCN Red List of Threatened Species 2016 e.T41257A45182533 Ochotona collaris
collared pika
This is a widespread species that is unlikely to be experiencing a decline significant enough to warrant listing under a threat category. Ochotona collaris occurs in remote regions of Alaska (USA) and northwestern Canada, where it is unlikely to be negatively influenced by human activities (Smith et al. 1990). It is possible that some local declines have been exacerbated by localized impacts of global warming on snow cover and shrub encroachment, and more work needs to be conducted to determine the severity and generality of these responses. DOI
102. Williamson, SN; Barrio, IC; Hik, DS; Gamon, JA. (2016) Phenology and species determine growing-season albedo increase at the altitudinal limit of shrub growth in the sub-Arctic.Glob. Change Biol. 22: 3621-3631 Phenology and species determine growing-season albedo increase at the altitudinal limit of shrub growth in the sub-Arctic
albedo; alpine tundra; Betula; growing season; phenology; Salix
Arctic warming is resulting in reduced snow cover and increased shrub growth, both of which have been associated with altered land surface-atmospheric feedback processes involving sensible heat flux, ground heat flux and biogeochemical cycling. Using field measurements, we show that two common Arctic shrub species (Betula glandulosa and Salix pulchra), which are largely responsible for shrub encroachment in tundra, differed markedly in albedo and that albedo of both species increased as growing season progressed when measured at their altitudinal limit. A moveable apparatus was used to repeatedly measure albedo at six precise spots during the summer of 2012, and resampled in 2013. Contrary to the generally accepted view of shrub-covered areas having low albedo in tundra, full-canopy prostrate B. glandulosa had almost the highest albedo of all surfaces measured during the peak of the growing season. The higher midsummer albedo is also evident in localized MODIS albedo aggregated from 2000 to 2013, which displays a similar increase in growing-season albedo. Using our field measurements, we show the ensemble summer increase in tundra albedo counteracts the generalized effect of earlier spring snow melt on surface energy balance by approximately 40%. This summer increase in albedo, when viewed in absolute values, is as large as the difference between the forest and tundra transition. These results indicate that near future (<50 years) changes in growing-season albedo related to Arctic vegetation change are unlikely to be particularly large and might constitute a negative feedback to climate warming in certain circumstances. Future efforts to calculate energy budgets and a sensible heating feedback in the Arctic will require more detailed information about the relative abundance of different ground cover types, particularly shrub species and their respective growth forms and phenology. DOI
101. Williamson, SN; Copland, L; Hik, DS. (2016) The accuracy of satellite-derived albedo for northern alpine and glaciated land covers.Polar Sci. 10: 262-269 The accuracy of satellite-derived albedo for northern alpine and glaciated land covers
Albedo variability; Tundra; Glacier; MODIS; alpine
Alpine and Arctic land cover can present a challenge for the validation of satellite-derived albedo measurements due, in part, to the complex terrain and logistical difficulty of accessing these regions. We compared measurements of albedo on transects from northern mountain land covers (snowfield, glacier ice, tundra, saline silt river delta), and over a large elevation range to the coincident 8-day MODIS (MCD43) albedo product. We also compared field measurements at snow covered sites to the coincident daily MODIS (MOD10A1) snow albedo product. For each transect, we measured a range of albedo values, with the least variability on the silt river delta (range = 0.084) and the largest over mid-elevation glacier ice (range = 0.307). The highest elevation snowfield (0.170) had nearly the same range of albedo values as tundra (0.164). The MODIS shortwave White Sky Albedo product (MCD43A3) was highly correlated with the field transect albedo (R-2 = 0.96), with a Root Mean Square Error (RMSE) of 0.061. The MODIS shortwave Black Sky Albedo product was similarly correlated with field transects (R-2 = 0.96; RMSE = 0.063). These results indicate that remote observation of albedo over snow covered and alpine terrain is well constrained and consistent with other studies. Albedo varied by 15% both spatially and temporally for the high elevation snowfields at the point in the season where albedo variation should be at its minimum. There were several instances where MCD43A3 albedo was not produced over snow and was instead classified as cloud covered, despite field observations of cloud free skies. There were also several instances where daily MOD10A1 albedo was produced during the coincident 8-day period at these locations. This suggests that the cloud mask in the MCD43 product is overly conservative over snow. Spatial variation in albedo within the MODIS grid cell (500 m), especially for snow and glacier ice, combined with the uncertainty associated with positional accuracy of MODIS, indicates that the accuracy of MODIS albedo will be dependent on both land cover type and the period of observation. (C) 2016 Elsevier B.V. and NIPR. All rights reserved. DOI
100. Barrio, IC; Hik, DS; Liu, Y. (2015) Diet breadth of Gynaephora groenlandica (Lepidoptera: Erebidae): is polyphagy greater in alpine versus Arctic populations?Can. Entomol. 147: 215-221 Diet breadth of Gynaephora groenlandica (Lepidoptera: Erebidae): is polyphagy greater in alpine versus Arctic populations?
alpine ; plants insects
Gynaephora groenlandica (Wocke) (Lepidoptera: Erebidae) is a cold-adapted species, whose life history traits are dictated by cold and short Arctic summers. We used a recently discovered alpine tundra population in southwestern Yukon, Canada to investigate local adaptations to habitats with different environmental conditions (alpine versus Arctic). Using cafeteria-type experiments and field observations we examined the diet breadth of alpine populations of G. groenlandica beringiana Schmidt and Cannings, and compared these to published data on High Arctic populations of G. groenlandica groenlandica and to the closely related G. rossii Curtis. Gynaephora groenlandica beringiana appears to have a broader diet than High Arctic populations, but similar to that exhibited by alpine populations of G. rossii. Such trends could emerge from reduced synchrony between herbivores and their host plants in less extreme environments, and possibly from a reduced incidence of parasitoids in the life cycle of these populations. Our findings indicate the larval host plant plasticity of G. groenlandica in different environments, and are relevant to predictions regarding the fate of these populations under climate warming scenarios. DOI
96. Kennicutt, MC; Chown, SL; Cassano, JJ; Liggett, D; Peck, LS; Massom, R; Rintoul, SR; Storey, J; Vaughan, DG; Wilson, TJ; Allison, I; Ayton, J; Badhe, R; Baeseman, J; Barrett, PJ; Bell, RE; Bertler, N; Bo, S; Brandt, A; Bromwich, D; Cary, SC; Clark, MS; Convey, P; Costa, ES; Cowan, D; Deconto, R; Dunbar, R; Elfring, C; Escutia, C; Francis, J; Fricker, HA; Fukuchi, M; Gilbert, N; Gutt, J; Havermans, C; Hik, D; Hosie, G; Jones, C; Kim, YD; Le Maho, Y; Lee, SH; Leppe, M; Leitchenkov, G; Li, X; Lipenkov, V; Lochte, K; Lopez-Martinez, J; Ludecke, C; Lyons, W; Marenssi, S; Miller, H; Morozova, P; Naish, T; Nayak, S; Ravindra, R; Retamales, J; Ricci, CA; Rogan-Finnemore, M; Ropert-Coudert, Y; Samah, AA; Sanson, L; Scambos, T; Schloss, IR; Shiraishi, K; Siegert, MJ; Simoes, JC; Storey, B; Sparrow, MD; Wall, DH; Walsh, JC; Wilson, G; Winther, JG; Xavier, JC; Yang, H; Sutherland, WJ. (2015) A roadmap for Antarctic and Southern Ocean science for the next two decades and beyond.Antarct. Sci. 27: 3-18 A roadmap for Antarctic and Southern Ocean science for the next two decades and beyond
extraordinary logistics; future directions; horizon scan; research priorities; Scientific Committee on Antarctic Research; technological challenges
Antarctic and Southern Ocean science is vital to understanding natural variability, the processes that govern global change and the role of humans in the Earth and climate system. The potential for new knowledge to be gained from future Antarctic science is substantial. Therefore, the international Antarctic community came together to 'scan the horizon' to identify the highest priority scientific questions that researchers should aspire to answer in the next two decades and beyond. Wide consultation was a fundamental principle for the development of a collective, international view of the most important future directions in Antarctic science. From the many possibilities, the horizon scan identified 80 key scientific questions through structured debate, discussion, revision and voting. Questions were clustered into seven topics: i) Antarctic atmosphere and global connections, ii) Southern Ocean and sea ice in a warming world, iii) ice sheet and sea level, iv) the dynamic Earth, v) life on the precipice, vi) near-Earth space and beyond, and vii) human presence in Antarctica. Answering the questions identified by the horizon scan will require innovative experimental designs, novel applications of technology, invention of next-generation field and laboratory approaches, and expanded observing systems and networks. Unbiased, non-contaminating procedures will be required to retrieve the requisite air, biota, sediment, rock, ice and water samples. Sustained year-round access to Antarctica and the Southern Ocean will be essential to increase winter-time measurements. Improved models are needed that represent Antarctica and the Southern Ocean in the Earth System, and provide predictions at spatial and temporal resolutions useful for decision making. A co-ordinated portfolio of cross-disciplinary science, based on new models of international collaboration, will be essential as no scientist, programme or nation can realize these aspirations alone. DOI
94. McGetrick, JA; Bubela, T; Hik, DS. (2015) Circumpolar stakeholder perspectives on Geographic Information Systems for communicating the health impacts of development.Environ. Sci. Policy 54: 176-184 Circumpolar stakeholder perspectives on Geographic Information Systems for communicating the health impacts of development
Circumpolar region; Indigenous peoples; Geographic Information Systems; Health impact assessment; Public health; Sustainable development
Natural resource development is accelerating in the circumpolar region, raising questions about the balance between potential economic benefits for northern indigenous peoples with the risks of increasing long-standing health inequities. New communication tools are needed to document and synthesize complex and diverse evidence of health impacts in a context relevant for natural resource management. Our research examines the perspectives of circumpolar experts on Geographic Information Systems (GIS) as a platform to synthesize and communicate scientific and indigenous knowledge. Thirty policy makers, academic researchers, and community-level practitioners participated in semi-structured interviews examining indigenous community health, natural resource management, and the use of GIS within Arctic and subarctic communities. Qualitative analysis of the interview transcripts for key themes indicated that the majority of circumpolar experts supported employing GIS to facilitate more extensive collaboration with indigenous communities and to produce higher quality data outputs for decision-making forums. To ensure GIS enables natural resource development decision-making to improve the social and economic welfare of indigenous people, experts recommended increasing communities' access to technology and training, community stewardship of data, utilizing data for ongoing monitoring of development impacts, and coordinating cumulative impact monitoring within regions. Findings focus on circumpolar natural resource management in jurisdictions with a mandate for public participation, with relevance to improving accountability to indigenous populations in other regions. (C) 2015 Elsevier Ltd. All rights reserved. DOI
93. Myers-Smith, IH; Elmendorf, SC; Beck, PSA; Wilmking, M; Hallinger, M; Blok, D; Tape, KD; Rayback, SA; Macias-Fauria, M; Forbes, BC; Speed, JDM; Boulanger-Lapointe, N; Rixen, C; Levesque, E; Schmidt, NM; Baittinger, C; Trant, AJ; Hermanutz, L; Collier, LS; Dawes, MA; Lantz, TC; Weijers, S; Jorgensen, RH; Buchwal, A; Buras, A; Naito, AT; Ravolainen, V; Schaepman-Strub, G; Wheeler, JA; Wipf, S; Guay, KC; Hik, DS; Vellend, M. (2015) Climate sensitivity of shrub growth across the tundra biome.Nat. Clim. Chang. 5: 887-+ Climate sensitivity of shrub growth across the tundra biome
Rapid climate warming in the tundra biome has been linked to increasing shrub dominance(1-4). Shrub expansion can modify climate by altering surface albedo, energy and water balance, and permafrost(2,5-8), yet the drivers of shrub growth remain poorly understood. Dendroecological data consisting of multi-decadal time series of annual shrub growth provide an underused resource to explore climate-growth relationships. Here, we analyse circumpolar data from 37 Arctic and alpine sites in 9 countries, including 25 species, and similar to 42,000 annual growth records from 1,821 individuals. Our analyses demonstrate that the sensitivity of shrub growth to climate was: (1) heterogeneous, with European sites showing greater summer temperature sensitivity than North American sites, and (2) higher at sites with greater soil moisture and for taller shrubs (for example, alders and willows) growing at their northern or upper elevational range edges. Across latitude, climate sensitivity of growth was greatest at the boundary between the Low and High Arctic, where permafrost is thawing(4) and most of the global permafrost soil carbon pool is stored(9). The observed variation in climate-shrub growth relationships should be incorporated into Earth system models to improve future projections of climate change impacts across the tundra biome. DOI
92. Myers-Smith, IH; Elmendorf, SC; Beck, PSA; Wilmking, M; Hallinger, M; Blok, D; Tape, KD; Rayback, SA; Macias-Fauria, M; Forbes, BC; Speed, JDM; Boulanger-Lapointe, N; Rixen, C; Levesque, E; Schmidt, NM; Baittinger, C; Trant, AJ; Hermanutz, L; Collier, LS; Dawes, MA; Lantz, TC; Weijers, S; Jorgensen, RH; Buchwal, A; Buras, A; Naito, AT; Ravolainen, V; Schaepman-Strub, G; Wheeler, JA; Wipf, S; Guay, KC; Hik, DS; Vellend, M. (2015) Climate sensitivity of shrub growth across the tundra biome (vol 5, pg 887, 2015).Nat. Clim. Chang. 5 Climate sensitivity of shrub growth across the tundra biome (vol 5, pg 887, 2015)
91. Patil, VP; Karels, TJ; Hik, DS. (2015) Ecological, Evolutionary and Social Constraints on Reproductive Effort: Are Hoary Marmots Really Biennial Breeders?PLoS One 10 Ecological, Evolutionary and Social Constraints on Reproductive Effort: Are Hoary Marmots Really Biennial Breeders?
Biennial breeding is a rare life-history trait observed in animal species living in harsh, unproductive environments. This reproductive pattern is thought to occur in 10 of 14 species in the genus Marmota, making marmots useful model organisms for studying its ecological and evolutionary implications. Biennial breeding in marmots has been described as an obligate pattern which evolved as a mechanism to mitigate the energetic costs of reproduction (Evolved Constraint hypothesis). However, recent anecdotal evidence suggests that it is a facultative pattern controlled by annual variation in climate and food availability (Environmental Constraint hypothesis). Finally, in social animals like marmots, biennial breeding could result from reproductive competition between females within social groups (Social Constraint hypothesis). We evaluated these three hypotheses using mark-recapture data from an 8-year study of hoary marmot (Marmota caligata) population dynamics in the Yukon. Annual variation in breeding probability was modeled using multi-state markrecapture models, while other reproductive life-history traits were modeled with generalized linear mixed models. Hoary marmots were neither obligate nor facultative biennial breeders, and breeding probability was insensitive to evolved, environmental, or social factors. However, newly mature females were significantly less likely to breed than older individuals. Annual breeding did not result in increased mortality. Female survival and, to a lesser extent, average fecundity were correlated with winter climate, as indexed by the Pacific Decadal Oscillation. Hoary marmots are less conservative breeders than previously believed, and the evidence for biennial breeding throughout Marmota, and in other arctic/alpine/antarctic animals, should be re-examined. Prediction of future population dynamics requires an accurate understanding of life history strategies, and of how life history traits allow animals to cope with changes in weather and other demographic influences. DOI
89. Elmendorf, SC; Henry, GHR; Hollister, RD; Alatalo, J; Bjork, RG; Bjorkman, AD; Callaghan, TV; Collier, LS; Cooper, EJ; Cornelissen, JHC; Day, TA; Fosaa, AM; Gould, WA; Gretarsdottir, J; Harte, J; Hermanutz, L; Hik, DS; Hofgaard, A; Jarrad, F; Jonsdottir, IS; Keuper, F; Klanderud, K; Klein, JA; Koh, S; Kudo, G; Lang, SI; Loewen, V; May, JL; Mercado, J; Michelsen, A; Molau, U; Myers-Smith, IH; Oberbauer, SF; Pieper, S; Post, E; Rixen, C; Robinson, CH; Schmidt, NM; Shaver, GR; Stenstrom, A; Tolvanen, A; Totland, O; Troxler, T; Wahren, CH; Walker, MD; Webber, PJ; Welker, JM; Wookey, PA. (2014) Global assessment of experimental climate warming on tundra vegetation: heterogeneity over space and time (vol 15, pg 164, 2012).Ecology Letters 17: 260-260 Global assessment of experimental climate warming on tundra vegetation: heterogeneity over space and time (vol 15, pg 164, 2012)
DOI
88. Wheeler, HC; Hik, DS. (2014) Giving-up densities and foraging behaviour indicate possible effects of shrub encroachment on arctic ground squirrels.Anim. Behav. 95: 1-8 Giving-up densities and foraging behaviour indicate possible effects of shrub encroachment on arctic ground squirrels
climate change; foraging; giving-up density; sciurid; shrub encroachment; Urocitellus parryii; vigilance
Behavioural responses of prey to predation risk are often mediated by vegetation structure. Erect woody shrubs are increasing in many arctic and alpine environments, and this change in habitat structure has the potential to alter perception of risk and fear for foraging herbivores. To assess the role of shrub cover in determining behavioural responses to foraging under predation risk, we used measurements of giving-up density (GUD) and video recordings of vigilance behaviour of individual Arctic ground squirrels, Urocitellus parryii, across an alpine tundra to shrub ecotone. Dense shrub habitat was associated with higher GUDs, implying that foraging costs were higher in dense shrub than in less shrub-dominated habitats. Foraging strategies differed between habitats, with a negative relationship between visibility and GUD in high-visibility, open-tundra habitats and a positive relationship between visibility and GUD in low-visibility, shrub-dominated habitats, which may be indicative of alternative foraging strategies in different habitats. Squirrels initially made a high investment in vigilance, which was independent of patch residence time. This presumably increases the costs of quitting patches earlier. In shrub-dominated habitat, erect bipedal forms of vigilance were also observed more frequently. Our results indicate that shrub encroachment into northern and alpine tundra may impose costs on foraging arctic ground squirrels and alter foraging strategies. (C) 2014 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. DOI
87. Wheeler, HC; Hik, DS. (2014) Influence of shrub canopies on growth rate and pre-hibernation mass of juvenile arctic ground squirrels.Wildlife Biol. 20: 253-258 Influence of shrub canopies on growth rate and pre-hibernation mass of juvenile arctic ground squirrels
The wide-spread encroachment of canopy-forming shrubs into northern and alpine tundra communities is likely to alter many plant-animal interactions, with direct and indirect impacts on herbivore populations. Specifically, shrub encroachment may impact habitat quality for herbivores by changing predation risk as a result of reduced visibility. We investigated the association between visibility and growth of juvenile arctic ground squirrels Urocitellus parryii across an alpine tundra ecotone with varying shrub cover. Marked individuals were weighed throughout the period following emergence from natal burrows in early summer until just prior to hibernation. Both males and females showed a positive association between habitat-specific visibility and post-emergence growth rate. There was a positive relationship between post-emergence juvenile growth rate and pre-hibernation mass for females but not males. As shrubs increase, ground squirrel populations may be adversely affected by reductions in habitat-scale visibility. DOI
86. Williamson, SN; Hik, DS; Gamon, JA; Kavanaugh, JL; Flowers, GE. (2014) Estimating Temperature Fields from MODIS Land Surface Temperature and Air Temperature Observations in a Sub-Arctic Alpine Environment.Remote Sens. 6: 946-963 Estimating Temperature Fields from MODIS Land Surface Temperature and Air Temperature Observations in a Sub-Arctic Alpine Environment
mean daily surface temperature; land surface temperature; air temperature; MODIS; meteorological station; tundra; Yukon Canada: alpine
Spatially continuous satellite infrared temperature measurements are essential for understanding the consequences and drivers of change, at local and regional scales, especially in northern and alpine environments dominated by a complex cryosphere where in situ observations are scarce. We describe two methods for producing daily temperature fields using MODIS. clear-sky. day-time Land Surface Temperatures (LST). The Interpolated Curve Mean Daily Surface Temperature (ICM) method, interpolates single daytime Terra LST values to daily means using the coincident diurnal air temperature curves. The second method calculates daily mean LST from daily maximum and minimum LST (MMM) values from MODIS Aqua and Terra. These ICM and MMM models were compared to daily mean air temperatures recorded between April and October at seven locations in southwest Yukon, Canada, covering characteristic alpine land cover types (tundra, barren, glacier) at elevations between 1,408 m and 2,319 m. Both methods for producing mean daily surface temperatures have advantages and disadvantages. ICM signals are strongly correlated with air temperature (R-2 = 0.72 to 0.86), but have relatively large variability (RMSE = 4.09 to 4.90 K), while MMM values had a stronger correlation to air temperature (R-2 = 0.90) and smaller variability (RMSE = 2.67 K). Finally, when comparing 8-day LST averages, aggregated from the MMM method, to air temperature, we found a high correlation (R-2 = 0.84) with less variability (RMSE = 1.54 K). Where the trend was less steep and the y-intercept increased by 1.6 degrees C compared to the daily correlations. This effect is likely a consequence of LST temperature averages being differentially affected by cloud cover over warm and cold surfaces. We conclude that satellite infrared skin temperature (e.g., MODIS LST), which is often aggregated into multi-day composites to mitigate data reductions caused by cloud cover, changes in its relationship to air temperature depending on the period of aggregation. DOI
85. Zgurski, JM; Hik, DS. (2014) Gene flow and the restoration of genetic diversity in a fluctuating collared pika (Ochotona collaris) population.Conserv. Genet. 15: 37-48 Gene flow and the restoration of genetic diversity in a fluctuating collared pika (Ochotona collaris) population
Density-dependent dispersal; Microsatellites; Ochotonidae; Population genetics; Ruby range; Spatial autocorrelation; Bottleneck
Changes in the density of small mammal populations can alter their genetic diversity and structure over time. Repeated density declines may gradually erode a population's genetic variability, and ultimately undermine its long-term viability. We investigated changes in the genetic diversity and structure of a fluctuating collared pika (Lagomorpha: Ochotona collaris) population over 12 years. There are concerns that the long-term persistence of the collared pika is at risk due to climate change, as pika populations are sensitive to environmental variability and inhabit a region undergoing particularly rapid warming. The study population declined abruptly during 2000 and 2003; however, it subsequently recovered and failed to show any genetic signature of having undergone a bottleneck. There was also no evidence for widespread inbreeding before or after the population declines. Using a spatial autocorrelation analysis, we also documented positive fine-scale genetic structure (<250 m) in the population during 7 out of the 12 years examined. Although the genetic structure is consistent with low average dispersal distances, a GeneClass2 analysis indicated that the collared pika population received immigrants from other populations, some of which survived and bred. Thus, like many other fluctuating small mammal populations, the collared pika population studied here appears to be resilient to density fluctuations. Dispersal distances were adequate for allowing gene flow into the study population and preventing declines in genetic variability. DOI
84. Barrio, IC; Hik, DS. (2013) Good neighbours? Determinants of aggregation and segregation among alpine herbivores.Ecoscience 20: 276-282 Good neighbours? Determinants of aggregation and segregation among alpine herbivores
alpine tundra; coexistence; facilitation; interspecific interactions; medium-sized mammals
Interspecific interactions often determine the structure and stability of biotic communities. In low-productivity and highly seasonal environments such as the alpine tundra, most interactions occur during a short, snow-free period. The strength and direction of these interactions are likely to be determined by the availability of resources, particularly among species of the same ecological guild. Understanding how species interact in such environments can provide insights into the conditions that facilitate their coexistence. We determined the potential for interspecific interactions among 3 resident medium-sized mammalian herbivores inhabiting the alpine tundra and investigated how they share available space and resources. Overlap in their respective activity areas indicated that these species were aggregated at a landscape scale, but other mechanisms allowed their coexistence at a finer scale. Their distributions were primarily associated with shorter distances to heterospecifics and, secondly, with habitat features related to shelter and escape from predation. Our results suggest that these species can (and do) coexist by partitioning their ecological niches. Competition is likely not a major factor in structuring these communities; in turn, facilitative mechanisms may allow co-occurrence of these sympatric herbivores in seasonal, low productivity environments. DOI
83. Barrio, IC; Hik, DS; Bueno, CG; Cahill, JF. (2013) Extending the stress-gradient hypothesis - is competition among animals less common in harsh environments?Oikos 122: 516-523 Extending the stress-gradient hypothesis - is competition among animals less common in harsh environments?
The role of positive interactions has become widely accepted as a mechanism shaping community dynamics. Most empirical evidence comes from plant communities and sessile marine organisms. However, evidence for the relative role of positive interactions in organizing terrestrial animal communities is more limited, and a general framework that includes positive interactions among animals is lacking. The stress gradient hypothesis' (SGH) developed by plant ecologists predicts that the balance between positive and negative interactions will vary along gradients of biotic and abiotic stress, with positive interactions being more important in stressful environments. Paralleling the SGH, stress gradients for terrestrial herbivores could be equated to inverse primary productivity gradients, so we would expect positive interactions to prevail in more stressful, low productivity environments. However, this contradicts the typical view of terrestrial animal ecology that low primary productivity systems will foster intense competition for resources among consumers. Here we use alpine herbivores as a case study to test one of the predictions of the SGH in animal communities, namely the prevalence of positive interactions in low productivity environments. We identify potential mechanisms of facilitation and review the limited number of examples of interspecific interactions among alpine herbivores to assess the role of positive and negative interactions in structuring their communities. A meta-analysis showed no clear trend in the strength and direction of interactions among alpine herbivores. Although studies were biased towards reporting significant negative inter actions, we found no evidence of competition dominating in harsh environments. Thus, our results only partially support the SGH, but directly challenge the dominant view among animal ecologists. Clearly, a sound theoretical framework is needed to include competition, positive and neutral interactions as potential mechanisms determining the structure of animal communities under differing environmental conditions, and the stress-gradient hypothesis can provide a solid starting point. DOI
82. Barrio, IC; Hik, DS; Peck, K; Bueno, CG. (2013) After the frass: foraging pikas select patches previously grazed by caterpillars.Biol. Lett. 9 After the frass: foraging pikas select patches previously grazed by caterpillars
facilitation; grazing succession; herbivory; indirect interactions
Interactions among herbivores can shape the structure of their communities and drive their dynamics. However, detecting herbivore interactions can be challenging when they are deferred in space or time. Moreover, interactions among distantly related groups of herbivores, such as vertebrates and invertebrates, are poorly understood. We investigated the effect of invertebrate herbivory on the subsequent foraging choices of a small alpine-dwelling vertebrate, the collared pika (Ochotona collaris). We carried out a field experiment within pika territories, by presenting them with a choice of foraging sites following manipulation of invertebrate (caterpillar) herbivory. Pikas actively selected areas with increased, recent invertebrate herbivory. While the underlying mechanisms behind this interaction remain unknown, our results demonstrate a positive effect of invertebrate herbivores on subsequent vertebrate foraging preferences for the first time. Even among distantly related taxa, such interactions where one herbivore is cueing on the foraging of another, could drive the creation of herbivory hotspots, with cascading consequences for ecosystem processes. DOI
81. Barrio, IC; Schmidt, BC; Cannings, S; Hik, DS. (2013) First Records of the Arctic Moth Gynaephora groenlandica (Wocke) South of the Arctic Circle: A New Alpine Subspecies.Arctic 66: 429-434 First Records of the Arctic Moth Gynaephora groenlandica (Wocke) South of the Arctic Circle: A New Alpine Subspecies
glacial refugia; Kluane; Lepidoptera; Lymantriinae; Ogilvie; range extension; relict populations: alpine
Two adjacent populations of the Arctic moth Gynaephora groenlandica, a High Arctic endemic species, were found in southwest Yukon, ca. 900 km south of the species' described distribution. Species identification was based on larval morphology for one population and on larvae rearing and DNA barcoding for the other. All three approaches clearly separated G. groenlandica from the closely related and frequently sympatric G. rossii. These records represent the first reports of G. groenlandica in alpine environments, and we recognize these populations as a distinct subspecies, G. g. beringiana, on the basis of differences in habitat, geography, wing phenotype, and DNA barcode. Given the limited dispersal ability of G. groenlandica, these records may represent isolated relict populations. Disjunct populations and new records of other species recently described for the southwest Yukon suggest 1) that this region is understudied and a potential refugium for species characteristic of different biogeographic influences and 2) that this region may be changing considerably in response to recent rapid environmental change, which has influenced species distribution, abundance, and phenology. Our findings, however, might result from a relatively poor description of the arthropod fauna of remote locations; these discoveries should therefore instigate further survey efforts.
79. Myers-Smith, IH; Hik, DS. (2013) Shrub canopies influence soil temperatures but not nutrient dynamics: An experimental test of tundra snow-shrub interactions.Ecol. Evol. 3: 3683-3700 Shrub canopies influence soil temperatures but not nutrient dynamics: An experimental test of tundra snow-shrub interactions
Alpine; arctic; birch (Betula); carbon; litter; nitrogen; permafrost; plant-soil (belowground) interactions; soil respiration; willow (Salix)
Shrubs are the largest plant life form in tundra ecosystems; therefore, any changes in the abundance of shrubs will feedback to influence biodiversity, ecosystem function, and climate. The snow-shrub hypothesis asserts that shrub canopies trap snow and insulate soils in winter, increasing the rates of nutrient cycling to create a positive feedback to shrub expansion. However, previous work has not been able to separate the abiotic from the biotic influences of shrub canopies. We conducted a 3-year factorial experiment to determine the influences of canopies on soil temperatures and nutrient cycling parameters by removing similar to 0.5m high willow (Salix spp.) and birch (Betula glandulosa) shrubs, creating artificial shrub canopies and comparing these manipulations to nearby open tundra and shrub patches. Soil temperatures were 4-5 degrees C warmer in January, and 2 degrees C cooler in July under shrub cover. Natural shrub plots had 14-33cm more snow in January than adjacent open tundra plots. Snow cover and soil temperatures were similar in the manipulated plots when compared with the respective unmanipulated treatments, indicating that shrub canopy cover was a dominant factor influencing the soil thermal regime. Conversely, we found no strong evidence of increased soil decomposition, CO2 fluxes, or nitrate or ammonia adsorbtion under artificial shrub canopy treatments when compared with unmanipulated open tundra. Our results suggest that the abiotic influences of shrub canopy cover alone on nutrient dynamics are weaker than previously asserted. DOI
78. Patil, VP; Morrison, SF; Karels, TJ; Hik, DS. (2013) Winter weather versus group thermoregulation: what determines survival in hibernating mammals?Oecologia 173: 139-149 Winter weather versus group thermoregulation: what determines survival in hibernating mammals?
Climate change; Cooperative breeding; Hoary marmot; Mark-recapture; Pacific decadal; oscillation; Snowpack; Survival; Social structure
For socially hibernating mammals, the effectiveness of huddling as a means of energy conservation should increase with group size. However, group size has only been linked to increased survival in a few hibernating species, and the relative importance of social structure versus winter conditions during hibernation remains uncertain. We studied the influence of winter weather conditions, social group composition, age-structure, and other environmental factors and individual attributes on the overwinter survival of hoary marmots (Marmota caligata) in the Yukon Territory, Canada. Juvenile hoary marmot survival was negatively correlated with the mean winter (November to May) Pacific Decadal Oscillation (PDO) index. Survival in older age-classes was negatively correlated with PDO lagged by 1 year. Social group size and structure were weakly correlated with survival in comparison to PDO. The relationship between winter PDO and survival was most likely due to the importance of snowpack as insulation during hibernation. The apparent response of hoary marmots to changing winter conditions contrasted sharply with those of other marmot species and other mammalian alpine herbivores. In conclusion, the severity of winter weather may constrain the effectiveness of group thermoregulation in socially hibernating mammals. DOI
77. Wheeler, HC; Hik, DS. (2013) Arctic ground squirrels Urocitellus parryii as drivers and indicators of change in northern ecosystems.Mammal Rev. 43: 238-255 Arctic ground squirrels Urocitellus parryii as drivers and indicators of change in northern ecosystems
Arctic ecosystems; climate change; population monitoring; Spermophilus parryii; trophic interactions
Global warming and increasing human activity are altering northern ecosystems. In these strongly seasonal environments, small herbivorous mammals may have a significant role in determining the trajectory of ecosystem transitions from one state to another. Arctic ground squirrels Urocitellus parryii are a key component of northern terrestrial food webs and are considered ecosystem engineers, exerting a large impact on their habitat through bioturbation. We review and synthesize diverse information about current and past distribution and density of arctic ground squirrels, their physiology and ecological interactions with other species. Factors that appear to affect the distribution and abundance of arctic ground squirrels include increasing temperatures, changes in flooding probability, permafrost thaw, shifting phenology, habitat change, new predators and invasive diseases. Increases in the distribution and density of arctic ground squirrels in northern latitudes and high altitudes could accelerate ecosystem change through facilitation of disturbance-tolerant species, while decreases in southern and milder climates could remove an important agent of disturbance and prey item. Despite their pervasive ecological influence throughout most of their range, arctic ground squirrels are underrepresented in ecological research, based on a comparison of the number of publications about arctic ground squirrels with the number about other species of the same genus, and about other arctic herbivores. The widespread distribution of arctic ground squirrels, along with their potential to exacerbate and alter trajectories of ecosystem change under global warming, makes them a valuable indicator of ecosystem change and therefore a candidate for increased monitoring. DOI
76. Williamson, SN; Hik, DS; Gamon, JA; Kavanaugh, JL; Koh, S. (2013) Evaluating Cloud Contamination in Clear-Sky MODIS Terra Daytime Land Surface Temperatures Using Ground-Based Meteorology Station Observations.J. Clim. 26: 1551-1560 Evaluating Cloud Contamination in Clear-Sky MODIS Terra Daytime Land Surface Temperatures Using Ground-Based Meteorology Station Observations
Environment Canada meteorological station hourly sampled air temperatures T-air at four stations in the southwest Yukon were used to identify cloud contamination in the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra clear-sky daytime land surface temperature (LST) and emissivity daily level-3 global 1-km grid product (MOD11A1, Collection 5) that is not flagged by the MODIS quality algorithm as contaminated. The additional cloud masking used qualitative ground-based sky condition observations, collected at two of the four stations, and coincident MODIS quality flag information. The results indicate that air temperature observed at a variety of discrete spatial locations having different land cover is highly correlated with MODIS LST collected at 1-km grid spacing. Quadratic relationships between LST and air temperature, constrained by ground observations of "clear" sky conditions, show less variability than relationships found under "mainly clear" and "mostly cloudy" sky conditions, and the more clouds observed in the sky coincides with a decreasing y intercept. Analysis of MODIS LST and its associated quality flags show a cold bias (<0 degrees C) in the assignment of the <= 3-K-average LST error, indicating MODIS LST has a maximum average error of <= 2 K over a warm surface (>0 degrees C). Analysis of two observation stations shows that unidentified clouds in MODIS LST are between 13% and 17%, a result that agrees well with previous studies. Analysis of daytime values is important because many processes are dependent on daylight and maximum temperature. The daytime clear-sky LST-T-air relationship observed for the good-quality confirmed cloud-free-sky MODIS LST quality flag can be used to discriminate cloud-contaminated grid cells beyond the standard MODIS cloud mask. DOI
75. Elmendorf, SC; Henry, GHR; Hollister, RD; Bjork, RG; Bjorkman, AD; Callaghan, TV; Collier, LS; Cooper, EJ; Cornelissen, JHC; Day, TA; Fosaa, AM; Gould, WA; Gretarsdottir, J; Harte, J; Hermanutz, L; Hik, DS; Hofgaard, A; Jarrad, F; Jonsdottir, IS; Keuper, F; Klanderud, K; Klein, JA; Koh, S; Kudo, G; Lang, SI; Loewen, V; May, JL; Mercado, J; Michelsen, A; Molau, U; Myers-Smith, IH; Oberbauer, SF; Pieper, S; Post, E; Rixen, C; Robinson, CH; Schmidt, NM; Shaver, GR; Stenstrom, A; Tolvanen, A; Totland, O; Troxler, T; Wahren, CH; Webber, PJ; Welker, JM; Wookey, PA. (2012) Global assessment of experimental climate warming on tundra vegetation: heterogeneity over space and time.Ecology Letters 15: 164-175 Global assessment of experimental climate warming on tundra vegetation: heterogeneity over space and time
Alpine; Arctic; climate warming; long-term experiment; meta-analysis; plants
Understanding the sensitivity of tundra vegetation to climate warming is critical to forecasting future biodiversity and vegetation feedbacks to climate. In situ warming experiments accelerate climate change on a small scale to forecast responses of local plant communities. Limitations of this approach include the apparent site-specificity of results and uncertainty about the power of short-term studies to anticipate longer term change. We address these issues with a synthesis of 61 experimental warming studies, of up to 20 years duration, in tundra sites worldwide. The response of plant groups to warming often differed with ambient summer temperature, soil moisture and experimental duration. Shrubs increased with warming only where ambient temperature was high, whereas graminoids increased primarily in the coldest study sites. Linear increases in effect size over time were frequently observed. There was little indication of saturating or accelerating effects, as would be predicted if negative or positive vegetation feedbacks were common. These results indicate that tundra vegetation exhibits strong regional variation in response to warming, and that in vulnerable regions, cumulative effects of long-term warming on tundra vegetation and associated ecosystem consequences have the potential to be much greater than we have observed to date. DOI
74. Elmendorf, SC; Henry, GHR; Hollister, RD; Bjork, RG; Boulanger-Lapointe, N; Cooper, EJ; Cornelissen, JHC; Day, TA; Dorrepaal, E; Elumeeva, TG; Gill, M; Gould, WA; Harte, J; Hik, DS; Hofgaard, A; Johnson, DR; Johnstone, JF; Jonsdottir, IS; Jorgenson, JC; Klanderud, K; Klein, JA; Koh, S; Kudo, G; Lara, M; Levesque, E; Magnusson, B; May, JL; Mercado-Diaz, JA; Michelsen, A; Molau, U; Myers-Smith, IH; Oberbauer, SF; Onipchenko, VG; Rixen, C; Schmidt, NM; Shaver, GR; Spasojevic, MJ; Porhallsdottir, PE; Tolvanen, A; Troxler, T; Tweedie, CE; Villareal, S; Wahren, CH; Walker, X; Webber, PJ; Welker, JM; Wipf, S. (2012) Plot-scale evidence of tundra vegetation change and links to recent summer warming.Nat. Clim. Chang. 2: 453-457 Plot-scale evidence of tundra vegetation change and links to recent summer warming
Temperature is increasing at unprecedented rates across most of the tundra biome(1). Remote-sensing data indicate that contemporary climate warming has already resulted in increased productivity over much of the Arctic(2,3), but plot-based evidence for vegetation transformation is not widespread. We analysed change in tundra vegetation surveyed between 1980 and 2010 in 158 plant communities spread across 46 locations. We found biome-wide trends of increased height of the plant canopy and maximum observed plant height for most vascular growth forms; increased abundance of litter; increased abundance of evergreen, low-growing and tall shrubs; and decreased abundance of bare ground. Intersite comparisons indicated an association between the degree of summer warming and change in vascular plant abundance, with shrubs, forbs and rushes increasing with warming. However, the association was dependent on the climate zone, the moisture regime and the presence of permafrost. Our data provide plot-scale evidence linking changes in vascular plant abundance to local summer warming in widely dispersed tundra locations across the globe. DOI
73. Gamon, JA; Kershaw, GP; Williamson, S; Hik, DS. (2012) Microtopographic patterns in an arctic baydjarakh field: do fine-grain patterns enforce landscape stability?Environ. Res. Lett. 7 Microtopographic patterns in an arctic baydjarakh field: do fine-grain patterns enforce landscape stability?
arctic tundra; microtopography; baydjarakh; high-centred polygons; permafrost; vegetation cover; landscape stability; remote sensing; albedo; thermal properties
Recent observations suggest that while some arctic landscapes are undergoing rapid change, others are apparently more resilient. In this study, we related surface cover and energy balance to microtopography in a degraded polygonal peat plateau (baydjarakh field) near Churchill, Manitoba in mid-summer 2010. The landscape consists of remnant high-centered polygons divided by troughs of varying widths. Historical aerial photos indicate these topographical features have been stable for over 80 years. Our goal was to explore patterns that might explain the apparent stability of this landscape over this time period and to evaluate remote sensing methods for characterizing microtopographic patterns that might resist change in the face of climate warming. Summertime surface albedo measurements were combined with several years of winter snow depth, snow heat flux, summer thaw depth and annual surface temperature, all of which had striking contrasts between wet troughs and high polygon centers. Measurements of albedo and the snowpack heat transfer coefficient were lowest for wet troughs (areas of standing water) dominated by graminoids, and were significantly higher for high polygon centers, dominated by dwarf shrubs and lichens. Snow depth, surface temperature and thaw depth were all significantly higher for wet troughs than high polygon centers. Together these patterns of cover and energy balance associated with microtopographic variation can contribute to the stability of this landscape through differential heat transfer and storage. We hypothesize that local thermal feedback effects, involving greater heat trapping in the troughs than on the baydjarakh tops, and effective insulation on the baydjarakh edges, have ensured landscape stability over most of the past century. These results suggest that high-resolution remote sensing, combined with detailed field monitoring, could provide insights into the dynamics or stability of arctic landscapes, where cover often varies over short distances due to microtopographic effects. DOI
72. Myers-Smith, IH; Hik, DS. (2012) UNIFORM FEMALE-BIASED SEX RATIOS IN ALPINE WILLOWS.Am. J. Bot. 99: 1243-1248 UNIFORM FEMALE-BIASED SEX RATIOS IN ALPINE WILLOWS
dioecy; female bias; Salicaceae; Salix (willow); sex ratios; spatial sex segregation: alpine plants
Premise of the study: The development of biased sex ratios in dioecious plant species has been ascribed to either (1) factors influencing differential adult mortality of male and female plants or (2) factors acting at an early life stage that determine seed sex ratio or seedling survival. Methods: To discriminate between these two competing hypotheses, we surveyed sex and age of 379 individuals from five species of the genus Salix across 11 alpine valleys in the southwest Yukon. Key results: We observed uniformly female-biased sex ratios of approximately 2:1 across all adult age cohorts and patch sizes of the five willow species. No spatial variation in sex ratio occurred that could be associated with site-specific characteristics such as elevation or aspect. Conclusions: Our results indicate that the female-biased sex ratios in the alpine willow species investigated in this study are not a consequence of ecological processes acting on established adult plants. The sex ratio is instead determined at an early life stage by a mechanism that remains unknown. DOI
71. Sheriff, MJ; Wheeler, H; Donker, SA; Krebs, CJ; Palme, R; Hik, DS; Boonstra, R. (2012) Mountain-top and valley-bottom experiences: the stress axis as an integrator of environmental variability in arctic ground squirrel populations.J. Zool. 287: 65-75 Mountain-top and valley-bottom experiences: the stress axis as an integrator of environmental variability in arctic ground squirrel populations
climate variation; fecal glucocorticoid metabolites; environmental stressors; population limitation; enzyme immunoassay validation: alpine
Environmental variation in mountainous regions can impose major differences in demography and physiology on animal populations that occupy a large elevation range. This variation can be both predictable and unpredictable. In the south-western Yukon, arctic ground squirrel (AGS) populations occur all the way from the forested valley bottoms to the alpine meadows and, in so doing, experience a wide range of predation risk, forage quality and exposure to weather variables. To assess how AGS integrate these factors and respond to them, we measured fecal glucocorticoid metabolites (FCM) as an index of the stress axis on four sites at different elevations. We first validated the enzyme immunoassay with a hormonal challenge protocol and a simulated predator stressor. AGS show a strong diurnal pattern in FCM levels, with peaks at mid-day and a marked increase in response to adrenocorticotropic hormone and the simulated predator and a decline in response to dexamethasone. The lag time between the challenge and its reflection in the feces was 412?h. Using this method in our field studies, we found that FCM levels decreased as the active season progressed; however, specific patterns differed among sites. We hypothesized that the early season peak in FCM levels followed by the general decline was due to brief, intense early season breeding, followed by the necessity of AGS to increase mass in preparation for hibernation. Although we found no clear, single explanation for the different FCM patterns among sites, we hypothesized that differences in seasonal climate and adverse weather may be major factors affecting FCM levels. The environment was markedly different between years, with 2008 being colder and wetter than 2009 and this was associated with AGS in 2008 having much higher FCM levels in general than 2009. We found that population density and visibility may also contribute. In conclusion, AGS live in a mosaic of habitats and each population is faced with a variety of environmental stressors; how they cope and respond to these stressors may not depend on a single factor but the complete aggregate of these stressors. DOI
70. Zgurski, JM; Hik, DS. (2012) Polygynandry and even-sexed dispersal in a population of collared pikas, Ochotona collaris.Anim. Behav. 83: 1075-1082 Polygynandry and even-sexed dispersal in a population of collared pikas, Ochotona collaris
collared pika; inbreeding; mating system; Ochotona collaris; sex-biased dispersal
Sex-biased dispersal is common in mammals, and in most species, the majority of dispersers are juvenile males. However, which sex typically disperses in a species will ultimately be determined by the costs and benefits of dispersal for each sex. These are partly determined by a species' mating system, with female-defence polygyny being strongly associated with male-biased dispersal. The few mammal species without sex-biased dispersal have been predicted to have a monogamous or polygynandrous mating system and levels of intraspecific competition that affect males and females equally. North American pikas may meet these criteria. Using microsatellite data from a decade of population monitoring, we examined the mating system and dispersal habits of the collared pika, Ochotona collaris, an asocial alpine-dwelling lagomorph. While their behaviour suggests they are monogamous or polygynous, parentage analyses revealed that the pikas were primarily polygynandrous. As predicted, there was no difference in the average distance dispersed by the two sexes, most likely because the costs and benefits of dispersal do not differ between males and females in this species. Since levels of inbreeding in the population were low, we also determined whether the pikas chose mates based on genetic dissimilarity, and whether they decreased the inbreeding coefficients of their offspring by going on forays to mate with animals other than their neighbours. Pikas did not restrict themselves to mating with their neighbours, but the average relatedness coefficients between pairs that produced offspring did not differ from the average relatedness coefficients expected under a model of random mate choice. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. DOI
69. Callaghan, TV; Tweedie, CE; Akerman, J; Andrews, C; Bergstedt, J; Butler, MG; Christensen, TR; Cooley, D; Dahlberg, U; Danby, RK; Daniels, FJA; de Molenaar, JG; Dick, J; Mortensen, CE; Ebert-May, D; Emanuelsson, U; Eriksson, H; Hedenas, H; Henry, GHR; Hik, DS; Hobbie, JE; Jantze, EJ; Jaspers, C; Johansson, C; Johansson, M; Johnson, DR; Johnstone, JF; Jonasson, C; Kennedy, C; Kenney, AJ; Keuper, F; Koh, S; Krebs, CJ; Lantuit, H; Lara, MJ; Lin, D; Lougheed, VL; Madsen, J; Matveyeva, N; McEwen, DC; Myers-Smith, IH; Narozhniy, YK; Olsson, H; Pohjola, VA; Price, LW; Riget, F; Rundqvist, S; Sandstrom, A; Tamstorf, M; Van Bogaert, R; Villarreal, S; Webber, PJ; Zemtsov, VA. (2011) Multi-Decadal Changes in Tundra Environments and Ecosystems: Synthesis of the International Polar Year-Back to the Future Project (IPY-BTF).Ambio 40: 705-716 Multi-Decadal Changes in Tundra Environments and Ecosystems: Synthesis of the International Polar Year-Back to the Future Project (IPY-BTF)
IPY; Glaciers; Permafrost; Snow stratigraphy; Tundra vegetation; Limnology; Shrubs; Treeline
Understanding the responses of tundra systems to global change has global implications. Most tundra regions lack sustained environmental monitoring and one of the only ways to document multi-decadal change is to resample historic research sites. The International Polar Year (IPY) provided a unique opportunity for such research through the Back to the Future (BTF) project (IPY project #512). This article synthesizes the results from 13 papers within this Ambio Special Issue. Abiotic changes include glacial recession in the Altai Mountains, Russia; increased snow depth and hardness, permafrost warming, and increased growing season length in sub-arctic Sweden; drying of ponds in Greenland; increased nutrient availability in Alaskan tundra ponds, and warming at most locations studied. Biotic changes ranged from relatively minor plant community change at two sites in Greenland to moderate change in the Yukon, and to dramatic increases in shrub and tree density on Herschel Island, and in sub-arctic Sweden. The population of geese tripled at one site in northeast Greenland where biomass in non-grazed plots doubled. A model parameterized using results from a BTF study forecasts substantial declines in all snowbeds and increases in shrub tundra on Niwot Ridge, Colorado over the next century. In general, results support and provide improved capacities for validating experimental manipulation, remote sensing, and modeling studies. DOI
68. Danby, RK; Koh, S; Hik, DS; Price, LW. (2011) Four Decades of Plant Community Change in the Alpine Tundra of Southwest Yukon, Canada.Ambio 40: 660-671 Four Decades of Plant Community Change in the Alpine Tundra of Southwest Yukon, Canada
Tundra; Yukon; Climate change; Arctic-alpine; Community ecology
Repeat measurements from long-term plots provide precise data for studying plant community change. In 2010, we visited a remote location in Yukon, Canada, where a detailed survey of alpine tundra communities was conducted in 1968. Plant community composition was resurveyed on the same four slopes using the same methods as the original study. Species richness and diversity increased significantly over the 42 years and non-metric multidimensional scaling indicated that community composition had also changed significantly. However, the direction and magnitude of change varied with aspect. Dominant species were not replaced or eliminated but, instead, declined in relative importance. Fine-scale changes in vegetation were evident from repeat photography and dendro-ecological analysis of erect shrubs, supporting the community-level analysis. The period of study corresponds to a mean annual temperature increase of 2 degrees C, suggesting that climate warming has influenced these changes. DOI
67. Myers-Smith, IH; Forbes, BC; Wilmking, M; Hallinger, M; Lantz, T; Blok, D; Tape, KD; Macias-Fauria, M; Sass-Klaassen, U; Levesque, E; Boudreau, S; Ropars, P; Hermanutz, L; Trant, A; Collier, LS; Weijers, S; Rozema, J; Rayback, SA; Schmidt, NM; Schaepman-Strub, G; Wipf, S; Rixen, C; Menard, CB; Venn, S; Goetz, S; Andreu-Hayles, L; Elmendorf, S; Ravolainen, V; Welker, J; Grogan, P; Epstein, HE; Hik, DS. (2011) Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities.Environ. Res. Lett. 6 Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities
shrubs; vegetation; tundra; Arctic; alpine; climate change; feedbacks; ecosystem structure; ecosystem function; disturbance
Recent research using repeat photography, long-term ecological monitoring and dendrochronology has documented shrub expansion in arctic, high-latitude and alpine tundra ecosystems. Here, we (1) synthesize these findings, (2) present a conceptual framework that identifies mechanisms and constraints on shrub increase, (3) explore causes, feedbacks and implications of the increased shrub cover in tundra ecosystems, and (4) address potential lines of investigation for future research. Satellite observations from around the circumpolar Arctic, showing increased productivity, measured as changes in 'greenness', have coincided with a general rise in high-latitude air temperatures and have been partly attributed to increases in shrub cover. Studies indicate that warming temperatures, changes in snow cover, altered disturbance regimes as a result of permafrost thaw, tundra fires, and anthropogenic activities or changes in herbivory intensity are all contributing to observed changes in shrub abundance. A large-scale increase in shrub cover will change the structure of tundra ecosystems and alter energy fluxes, regional climate, soil-atmosphere exchange of water, carbon and nutrients, and ecological interactions between species. In order to project future rates of shrub expansion and understand the feedbacks to ecosystem and climate processes, future research should investigate the species or trait-specific responses of shrubs to climate change including: (1) the temperature sensitivity of shrub growth, (2) factors controlling the recruitment of new individuals, and (3) the relative influence of the positive and negative feedbacks involved in shrub expansion. DOI
66. Myers-Smith, IH; Hik, DS; Kennedy, C; Cooley, D; Johnstone, JF; Kenney, AJ; Krebs, CJ. (2011) Expansion of Canopy-Forming Willows Over the Twentieth Century on Herschel Island, Yukon Territory, Canada.Ambio 40: 610-623 Expansion of Canopy-Forming Willows Over the Twentieth Century on Herschel Island, Yukon Territory, Canada
Arctic; Tundra; Climate change; Willows (Salix spp.); Shrub encroachment; Yukon
Canopy-forming shrubs are reported to be increasing at sites around the circumpolar Arctic. Our results indicate expansion in canopy cover and height of willows on Herschel Island located at 70 degrees north on the western Arctic coast of the Yukon Territory. We examined historic photographs, repeated vegetation surveys, and conducted monitoring of long-term plots and found evidence of increases of each of the dominant canopy-forming willow species (Salix richardsonii, Salix glauca and Salix pulchra), during the twentieth century. A simple model of patch initiation indicates that the majority of willow patches for each of these species became established between 1910 and 1960, with stem ages and maximum growth rates indicating that some patches could have established as late as the 1980s. Collectively, these results suggest that willow species are increasing in canopy cover and height on Herschel Island. We did not find evidence that expansion of willow patches is currently limited by herbivory, disease, or growing conditions. DOI
65. Loehr, J; Carey, J; O'Hara, RB; Hik, DS. (2010) The role of phenotypic plasticity in responses of hunted thinhorn sheep ram horn growth to changing climate conditions.J. Evol. Biol. 23: 783-790 The role of phenotypic plasticity in responses of hunted thinhorn sheep ram horn growth to changing climate conditions
climate change; horn; hunting; Ovis dalli; phenotypic plasticity
When phenotypic change occurs over time in wildlife populations, it can be difficult to determine to what degree it is because of genetic effects or phenotypic plasticity. Here, we assess phenotypic changes over time in horn length and volume of thinhorn sheep (Ovis dalli) rams from Yukon Territory, Canada. We considered 42 years of horn growth from over 50 000 growth measurements in over 8000 individuals. We found that weather explained a large proportion of the annual fluctuation in horn growth, being particularly sensitive to spring weather. Only 2.5% of variance in horn length growth could be explained by an individual effect, and thus any genetic changes over the time period could only have had a small effect on phenotypes. Our findings allow insight into the capacity for horn morphology to react to selection pressures and demonstrate the overall importance of climate in determining growth. DOI
64. Trefry, SA; Hik, DS. (2010) Variation in pika (Ochotona collaris, O-princeps) vocalizations within and between populations.Ecography 33: 784-795 Variation in pika (Ochotona collaris, O-princeps) vocalizations within and between populations
Understanding geographic call variation can resolve evolutionary and behavioural questions, yet the factors influencing divergent acoustic signals remain poorly understood in mammals. We explored call variation between collared pikas in Yukon and Alaska and American pikas in Alberta, and between individuals within a population of collared pikas. Classification trees were used to determine the extent of call divergence between populations and the elements of calls driving these differences. Pika populations had significant differences in call structure, and individual pikas were classified to their correct populations with up to 94% accuracy. To investigate possible mechanisms responsible for interspecific variability, we tested the acoustic adaptation hypothesis by using a playback experiment to explore whether American and collared pika calls transmit with less degradation across their own species' habitat than the habitat of their congener. We found no support for the acoustic adaptation hypothesis. Geographic call variation in these two species of pikas likely reflects genetic divergence, and may be a result of separate evolutionary histories. We calculated the potential for individual coding for both time and frequency measurements of calls. High frequency harmonics showed greater between- than within-individual variation, and may act as sources of information regarding individual identity. DOI
63. Mitchell, MGE; Cahill, JF; Hik, DS. (2009) Plant interactions are unimportant in a subarctic-alpine plant community.Ecology 90: 2360-2367 Plant interactions are unimportant in a subarctic-alpine plant community
Artemisia norvegica; Carex consimilis; community structure; competition; facilitation; importance; intensity; plant interactions; regression trees; subarctic-alpine; Yukon, Canada
We investigated whether plant interaction intensity in a subarctic-alpine meadow is important for determining community structure and species abundance. Using two common species as phytometers, we measured interaction intensity using a neighbor removal approach. Eight biotic and abiotic variables known to influence species abundance and community structure were measured, with regression trees used to examine how plant interactions and the biotic and abiotic variables were related to species evenness, richness, and phytometer spatial cover. A range of interactions was present, with both strong competition and facilitation present over small-scale abiotic and biotic gradients. Despite the variation in interaction intensity, it was generally unrelated to either community structure or phytometer cover. In other words, plant interactions were intense in many cases but were not important to community structure. This may be due to the prevalence of clonal species in this system and the influence of previous year's interactions on plant survival and patterns of community structure. These results also suggest how conflicting theories of the role of competition in unproductive environments may be resolved. Our findings suggest that plant interactions may be intense in reducing individual growth, while simultaneously not important in the context of community structure. Plant interactions need to be viewed and tested relative to other factors and stresses to accurately evaluate their importance in plant communities, with continued differentiation between the intensity of plant interactions and their relative importance in communities. DOI
62. Morrison, SF; Pelchat, G; Donahue, A; Hik, DS. (2009) Influence of food hoarding behavior on the over-winter survival of pikas in strongly seasonal environments.Oecologia 159: 107-116 Influence of food hoarding behavior on the over-winter survival of pikas in strongly seasonal environments
Alpine; Classification tree; Lagomorph; Ochotona collaris; Yukon
Food hoarding is a behavioral adaptation of some herbivores to manage food availability through time and space. In strongly seasonal environments, where summer growing seasons are short relative to winter, an earlier start to hoarding should increase the amount of vegetation stored for winter and improve subsequent survival. We examined hoarding behavior ('haying') and its impact on survival for a small alpine lagomorph, the collared pika (Ochotona collaris) in Yukon, Canada. We used a combination of video surveillance, haypile measurements, and survival data from marked individuals of known age and sex. Annual haypile initiation was strongly influenced by age and year. Adult pikas began haying an average of 16 days earlier in 2004 relative to 2005, whereas young of the year (juveniles) did not vary in the timing of haypile initiation. The mean haying rate per hour increased monthly from 3.7 +/- A 0.7 trips in June to 6.6 +/- A 0.8 trips in August. Simulation analysis estimated the median haypile mass (dry weight) by mid-September to be 5.5 kg. At least 75% of simulated haypiles had a minimum of 90 days (3 months) of food reserves, and 50% of simulated haypiles had a minimum of 177 days (5.9 months) of food reserves by mid-September, supporting the hypothesis that haypiles serve as the primary source of food during winter. Survival was greatest for pikas in 2005 when they began haying prior to 31 July, but the benefits of earlier accumulation of vegetation on survival also varied between years. The implications of earlier spring snowmelt are discussed with respect to pika foraging and overwinter survival. DOI
61. Post, E; Forchhammer, MC; Bret-Harte, MS; Callaghan, TV; Christensen, TR; Elberling, B; Fox, AD; Gilg, O; Hik, DS; Hoye, TT; Ims, RA; Jeppesen, E; Klein, DR; Madsen, J; McGuire, AD; Rysgaard, S; Schindler, DE; Stirling, I; Tamstorf, MP; Tyler, NJC; van der Wal, R; Welker, J; Wookey, PA; Schmidt, NM; Aastrup, P. (2009) Ecological Dynamics Across the Arctic Associated with Recent Climate Change.Science 325: 1355-1358 Ecological Dynamics Across the Arctic Associated with Recent Climate Change
At the close of the Fourth International Polar Year, we take stock of the ecological consequences of recent climate change in the Arctic, focusing on effects at population, community, and ecosystem scales. Despite the buffering effect of landscape heterogeneity, Arctic ecosystems and the trophic relationships that structure them have been severely perturbed. These rapid changes may be a bellwether of changes to come at lower latitudes and have the potential to affect ecosystem services related to natural resources, food production, climate regulation, and cultural integrity. We highlight areas of ecological research that deserve priority as the Arctic continues to warm. DOI
60. Trefry, SA; Hik, DS. (2009) Eavesdropping on the Neighbourhood: Collared Pika (Ochotona collaris) Responses to Playback Calls of Conspecifics and Heterospecifics.Ethology 115: 928-938 Eavesdropping on the Neighbourhood: Collared Pika (Ochotona collaris) Responses to Playback Calls of Conspecifics and Heterospecifics
The acoustic environment, composed in part by the vocalizations of sympatric animals, is a major source of information and can be used to fine-tune behavioural decisions. Active assessment of alarm calls within and between mammal species is not fully understood. We explored the behavioural responses of collared pikas to con- and heterospecific vocalizations, in order to determine whether they selectively attend to these calls. Pikas increased their vigilance after playback of alarm calls of heterospecific mammals (marmots and ground squirrels), but responded most strongly to conspecific calls. While responses to playback calls of their own, of neighbours and of a stranger did not differ, pikas did discriminate between individual callers in a habituation-discrimination experiment. The ability to make use of information from different sources in their acoustic environment likely facilitates pikas' behavioural decisions that affect foraging, predator avoidance and nepotism. DOI
59. Zgurski, JM; Davis, CS; Hik, DS. (2009) Isolation and characterization of microsatellite loci for the collared pika (Ochotona collaris) and their cross-amplification in five other Ochotona species.Mol. Ecol. Resour. 9: 867-871 Isolation and characterization of microsatellite loci for the collared pika (Ochotona collaris) and their cross-amplification in five other Ochotona species
genetic structure; metapopulations; microsatellites; Ochotona; Ochotonidae; pikas
We developed primers for eight polymorphic microsatellite loci isolated from the collared pika, Ochotona collaris, and also tested nine loci previously developed for the American pika, O. princeps, for use in O. collaris. Forty-six individuals from an O. collaris population in the southern Yukon were genotyped using all 17 loci. The average number of alleles per locus was six and the average observed heterozygosity was 0.59. All loci were tested for use in four Asian pika species and all but two loci amplified reliably in these species. DOI
58. Boonstra, R; Desantis, L; Krebs, CJ; Hik, DS. (2008) Climate and nutrient influences on the growth of white spruce trees in the boreal forests of the Yukon.Clim. Res. 36: 123-130 Climate and nutrient influences on the growth of white spruce trees in the boreal forests of the Yukon
climate change; nitrogen limitation; Picea glauca; primary productivity; spruce bark beetle; tree ring widths; Yukon; Kluane Lake; white spruce
The boreal forests of North America are undergoing major changes because of the direct effects of global warming and increased CO2 levels. Plant production in the boreal forest is nutrient limited, and we examined how long-term fertilization affected growth of white spruce Picea glauca in the face of these major changes. We conducted a large-scale experiment by fertilizing two 1 km(2) stands of white spruce in the southwestern Yukon with commercial NPK fertilizer from 1987 to 1994, Tree growth was measured by the width of annual increments in 60 trees from each of 2 control and of 2 matched fertilized 1 km(2) sites for the period from 1977 to 1997 in a before, during, and after experimental design. Ring widths increased in both control and fertilized trees over this period as summer temperatures increased. Ring widths in fertilized trees increased from 9 to 48 % over control trees during the years in which fertilizer was added, but immediately fell back to control levels from 1995 to 1997 at 1 site as soon as fertilization was stopped. In the long term, nitrogen in these forests may become tied up in shrubs, grasses, herbs, and fungi and not be available to the trees. There are 2 other possible explanations for this lack of sustained tree growth: first, the conversion of nitrogen into a form not readily available to spruce and, second, a spruce bark beetle outbreak that hit the southwestern Yukon during and after 1994 and affected 1 study site much more than the other. DOI
57. Frame, PF; Cluff, HD; Hik, DS. (2008) Wolf reproduction in response to caribou migration and industrial development on the central barrens of mainland Canada.Arctic 61: 134-142 Wolf reproduction in response to caribou migration and industrial development on the central barrens of mainland Canada
wolf; Canis lupus; caribou; Rangifer tarandus; cumulative effects; disturbance; migration; Northwest Territories; Nunavut; predator-prey; reproductive success
Reproductive success of mammals is greatly influenced by food availability. Where wolves (Canis lupus) prey on migratory barren-ground caribou (Rangifer tarandus), caribou migration patterns strongly influence food availability for wolves. However, industrial development in formerly undeveloped wolf range could also negatively influence wolf reproduction, either directly (by disrupting normal feeding behavior) or indirectly (by impacting caribou migrations). We used a cross-sectional time-series regression to analyze eight years of wolf reproductive data with respect to spatial and temporal variation in caribou migration and economic development in a 49 900 km(2) area of the Northwest Territories, Canada. Reproductive success decreased as the distance from wolf dens to caribou migration routes increased, while the timing of caribou migrations had little effect. There was no measurable effect of current levels of economic development on reproductive success, although evidence suggests the potential for indirect effects. Continued monitoring is required to identify possible thresholds of adverse effects for wolf populations.
56. Hudson, JMG; Morrison, SF; Hik, DS. (2008) Effects of leaf size on forage selection by collared pikas, Ochotona collaris.Arct. Antarct. Alp. Res. 40: 481-486 Effects of leaf size on forage selection by collared pikas, Ochotona collaris
We examined the influence of leaf size on forage selection by collared pikas (Ochotona collaris) living in alpine meadows in the Yukon Territory, Canada, by comparing the winter diets of individually recognized pikas to the available vegetation within their territories and by conducting cafeteria-style preference experiments. Pikas consistently preferred forage with larger leaves in the cafeteria trials. They also collected larger leaves from deciduous shrubs and graminoid species compared to other plant types such as lichens and evergreen shrubs for their winter diets. Pikas assessed differences in leaf size when selecting their winter diets and this appears to be an energetically efficient foraging strategy for surviving seasonal food scarcity. DOI
54. Morrison, SF; Hik, DS. (2008) Discrimination of intra- and inter-specific forage quality by collared pikas (Ochotona collaris).Can. J. Zool.-Rev. Can. Zool. 86: 456-461 Discrimination of intra- and inter-specific forage quality by collared pikas (Ochotona collaris)
The specific nutritional characteristics by which herbivores evaluate their foraging options are complex. We experimentally manipulated the crude protein and water content of two forage species (Carex consimilis Holm. (= Carex bigelowii Torr. ex Schwein.) and Polygonum bistorta L.) commonly cached by collared pikas (Ochotona collaris (Nelson, 1893)) to determine their influence on inter- and intra-specific forage selection. Preference data were collected for 27 pikas using cafeteria-style feeding trials in a randomized block design. A three-way interaction (species x protein x water) suggested that pikas made conditional forage selection decisions while caching these plants. The interaction was driven by greater selection for fresh rather than dried C. consimilis when both were not fertilized. Water content had no effect on the selection of either fertilized C. consimilis or fertilized P. bistorta. Overall, our results indicate that pikas made subtle decisions about their selection of vegetation during caching, based on variation in nitrogen and water content in addition to species-specific selection criteria. Further, our results imply that tests of foraging theory may need to consider intra-specific variation in forage characteristics, as well as inter-specific ranking of forage species. DOI
53. Weir, JN; Morrison, SE; Hik, DS. (2008) Linking foraging behavior to population density: An assessment of GMM models for Dall sheep.Ecol. Model. 211: 396-402 Linking foraging behavior to population density: An assessment of GMM models for Dall sheep
dall sheep; forage; metaphysiological models; Ovis dalli dalli; plant-herbivore; population density; Yukon
We adapted Owen-Smith's general growth-metabolism-mortality (GMM) model to estimate the abundance of a population of Dall sheep (Ovis dalli dalli) in the southwest Yukon, Canada. Estimated sheep densities using the GMM approach (18 - 32 sheep/km(2)) approximated longterm aerial survey data (20.2 - 29.6 sheep/km(2)) when biologically realistic levels of parameter variation were introduced. Sheep population growth rate based on the GMM model was most sensitive to the metabolic conversion of forage into sheep biomass, rate of vegetation attrition, and mortality rate during winter. Model estimates may be improved with better estimates of metabolic conversion of forage into sheep body mass, vegetation attrition, incorporation of inter-annual variability and stratification by sex and age classes. Overall, GMM models using mechanistic physiological and behavioral information may provide a complimentary approach to aerial censuses for estimating ungulate population abundance. (c) 2007 Elsevier B.V. All rights reserved. DOI
52. Cornelissen, JHC; van Bodegom, PM; Aerts, R; Callaghan, TV; van Logtestijn, RSP; Alatalo, J; Chapin, FS; Gerdol, R; Gudmundsson, J; Gwynn-Jones, D; Hartley, AE; Hik, DS; Hofgaard, A; Jonsdottir, IS; Karlsson, S; Klein, JA; Laundre, J; Magnusson, B; Michelsen, A; Molau, U; Onipchenko, VG; Quested, HM; Sandvik, SM; Schmidt, IK; Shaver, GR; Solheim, B; Soudzilovskaia, NA; Stenstrom, A; Tolvanen, A; Totland, O; Wada, N; Welker, JM; Zhao, XQ. (2007) Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes.Ecology Letters 10: 619-627 Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes
alpine; carbon; circum-arctic; global change; growth form; litter turnover; mass loss; vegetation change
Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide. Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition. DOI
51. Danby, RK; Hik, DS. (2007) Evidence of recent treeline dynamics in southwest Yukon from aerial photographs.Arctic 60: 411-420 Evidence of recent treeline dynamics in southwest Yukon from aerial photographs
climate change; forest-tundra; ecotones; timberline; repeat photography; air photos; landscape change; Yukon; Picea glauca
Small-scale vertical aerial photographs taken in 1947 and 1948 covering 200 km(2) of the Kluane Ranges, southwest Yukon, were compared with corresponding photographs taken in 1989 for the purpose of characterizing changes in the distribution and abundance of white spruce (Picea glauca (Moench) Voss) at the alpine treeline. Digital photogrammetry, including orthorectification and on-screen interpretation, was supplemented by stereoscopic inspection of the original prints. Qualitative assessment of change across nine image pairs was accompanied by quantitative analysis of changes in spruce density and elevation using 1 hectare plots and 100 m wide elevational belt transects, respectively, superimposed on the orthorectified images. Significant changes were observed over the 41 years, but the degree of change varied throughout the study area. The most common changes were an increase in canopy size of individual trees and an increase in stand density resulting from the establishment of new individuals. Several instances of treeline advance were also observed. An absence of major natural disturbances or widespread land use change indicates that treeline change is attributable to climate. Results from concurrent dendroecological studies indicate that these dynamics represent only part of the total extent of change to occur during the 20th century.
50. Danby, RK; Hik, DS. (2007) Variability, contingency and rapid change in recent subarctic alpine tree line dynamics.J. Ecol. 95: 352-363 Variability, contingency and rapid change in recent subarctic alpine tree line dynamics
climate change; dendroecology; ecotones; forest-tundra; non-linearity; Picea glauca; Salix glauca; stand dynamics; timberline; Yukon: alpine
Boundaries between forest and tundra ecosystems, tree lines, are expected to advance in altitude and latitude in response to climate warming. However, varied responses to 20th century warming suggest that in addition to temperature, tree line dynamics are mediated by species-specific traits and environmental conditions at landscape and local scales. We examined recent tree line dynamics at six topographically different, but climatically similar, sites in south-west Yukon, Canada. Dendroecological techniques were used to reconstruct changes in density of the dominant tree species, white spruce (Picea glauca), and to construct static age distributions of willow (Salix spp.), one of two dominant shrub genera. Data were analysed to identify periods and rates of establishment and mortality and to relate these to past climate. Tree line elevation and stand density increased significantly during the early to mid 20th century. However, this change was not uniform across sites. Spruce advanced rapidly on south-facing slopes and tree line rose 65-85 m in elevation. Tree line did not advance on north-facing slopes, but stand density increased 40-65%. Differences observed between aspects were due primarily to the differential presence of permafrost. Additional variability among sites was related to slope and vegetation type. Results were less conclusive for willow, but evidence for an advance was found at two sites. Increases in stand density were strongly correlated with summer temperatures. The period of rapid change coincided with a 30-year period of above average temperatures, beginning in 1920. The highest correlations were obtained using a forward average of 30-50 years, supporting the hypothesis that tree line dynamics are controlled more by conditions influencing recruitment than by establishment alone. The changes observed at several sites are suggestive of a threshold response and challenge the notion that tree lines respond gradually to climate warming. Overall, the results provide further evidence to support the idea that the pattern and timing of change is contingent on local, landscape, and regional-scale factors, as well as species' biology. DOI
49. Danby, RK; Hik, DS. (2007) Responses of white spruce (Picea glauca) to experimental warming at a subarctic alpine treeline.Glob. Change Biol. 13: 437-451 Responses of white spruce (Picea glauca) to experimental warming at a subarctic alpine treeline
climate change; experimental warming; open-top chamber; Picea glauca; seedling growth; timberline; treeline dynamics; Yukon: alpine
From 2001 to 2004 we experimentally warmed 40 large, naturally established, white spruce [Picea glauca (Moench) Voss] seedlings at alpine treeline in southwest Yukon, Canada, using passive open-top chambers (OTCs) distributed equally between opposing north and south-facing slopes. Our goal was to test the hypothesis that an increase in temperature consistent with global climate warming would elicit a positive growth response. OTCs increased growing season air temperatures by 1.8 degrees C and annual growing degree-days by one-third. In response, warmed seedlings grew significantly taller and had higher photosynthetic rates compared with control seedlings. On the south aspect, soil temperatures averaged 1.0 degrees C warmer and the snow-free period was nearly 1 month longer. These seedlings grew longer branches and wider annual rings than seedlings on the north aspect, but had reduced Photosystem-II efficiency and experienced higher winter needle mortality. The presence of OTCs tended to reduce winter dieback over the course of the experiment. These results indicate that climate warming will enhance vertical growth rates of young conifers, with implications for future changes to the structure and elevation of treeline contingent upon exposure-related differences. Our results suggest that the growth of seedlings on north-facing slopes is limited by low soil temperature in the presence of permafrost, while growth on south-facing slopes appears limited by winter desiccation and cold-induced photoinhibition. DOI
48. Frame, PF; Cluff, HD; Hik, DS. (2007) Response of wolves to experimental disturbance at homesites.J. Wildl. Manage. 71: 316-320 Response of wolves to experimental disturbance at homesites
anthropogenic disturbance; Canis lupus; habituation; homesite; industrial development; reproductive success; wolf
Events during the denning period (parturition to first autumn) often determine the reproductive success of wolves (Canis lupus). Consequently, there is concern about the potential adverse effects of human-caused disturbance at wolf den and rendezvous sites (homesites), but relatively little information on this subject is available. We conducted standardized experimental disturbance treatments at 12 unique wolf homesites in the Northwest Territories, Canada, during summers 2002 and 2003. The treatment consisted of an intruder approaching a homesite once per day for 3 consecutive days and recording behavioral responses, response distance, and response intensity of wolves. We counted pups and estimated their ages prior to the initial treatment at each site. Adult wolves moved pups at 3 of 6 treated homesites in each year. The amount and type of known human activity within a pack's home range did not influence whether adults moved pups in response to the treatment. The response intensity of wolves to the treatment was inversely related to the amount of human activity near a homesite. There was no relationship between the distance at which wolves responded to the intruder and the amount or type of human activity. There was a positive relationship between increasing age of pups and their relocation in response to the treatment. Reproductive success was not influenced by the treatment or by the amount and type of human activity. Treated sites were used by wolves the following year in the same proportion as untreated sites. It appears that pups are most vulnerable early in the year when less mobile; therefore, managers should consider age of pups before human activity at or near wolf homesites occurs. DOI
47. Koh, S; Hik, DS. (2007) Herbivory mediates grass-endophyte relationships.Ecology 88: 2752-2757 Herbivory mediates grass-endophyte relationships
endophytic fungi; Festuca altaica; herbivory; mutualism; Neotyphodium; optimal defense theory; subarctic; symbiosis
Endophytic fungi are plant symbionts living asymptomatically within plant tissues. Neotyphodium spp., which are asexual vertically transmitted systemic fungal endophytes of cool-season grasses, are predicted to be plant mutualists. These endophytes increase host plant resistance to environmental stresses and/or increase the production of alkaloid-based herbivore deterrents. The ubiquity of this defense mutualism is unclear, and a variety of alternative mechanisms may explain the observed variation in infection rates, levels of deterrence, and the maintenance of asexual endophytes in grass populations. We found that grass-endophyte interactions are variable and ordered along an herbivory gradient in an undisturbed subarctic alpine ecosystem. Native grass populations in grazed sites had significantly greater frequency of Neotyphodium infection compared to ungrazed sites. Tillers from grazed sites had significantly higher hyphal densities compared to ungrazed sites. The ability of grass-Neotyphodium constituents to deter vertebrate herbivory in natural systems is thought to be rare. In grazed meadows, we showed that endophyte infection resulted in the deterrence of grazing by native vertebrate herbivores. However, the same herbivores did not distinguish between infected and uninfected grass harvested from ungrazed areas. These results demonstrate that the relationship between vertically transmitted endophytes and grasses in the alpine tundra vary greatly within populations. This may be based in part on defense mutualism and is consistent, under varying levels of herbivory, with the predictions of optimal defense theory. DOI
46. Kyle, CJ; Karels, TJ; Davis, CS; Mebs, S; Clark, B; Strobeck, C; Hik, DS. (2007) Social structure and facultative mating systems of hoary marmots (Marmota caligata).Mol. Ecol. 16: 1245-1255 Social structure and facultative mating systems of hoary marmots (Marmota caligata)
hoary marmot; Marmota caligata; mating system; microsatellites; parentage; social structure
Mate-choice theory predicts different optimal mating systems depending on resource availability and habitat stability. Regions with limited resources are thought to promote monogamy. We tested predictions of monogamy in a social rodent, the hoary marmot (Marmota caligata), at the northern climatic extreme of its distribution. Mating systems, social structure and genetic relationships were investigated within and among neighbouring colonies of marmots within a 4 km(2) valley near Kluane National Park, Yukon, Canada, using 21 microsatellite loci. While both monogamous and polygynous populations of hoary marmots have been observed in the southern reaches of this species' range; northern populations of this species are thought to be predominantly monogamous. Contrary to previous studies, we did not find northern hoary marmot social groups to be predominantly monogamous; rather, the mating system seemed to be facultative, varying between monogamy and polygyny within, as well as among, social groups. These findings reveal that the mating systems within colonies of this species are more flexible than previously thought, potentially reflecting local variation in resource availability. DOI
45. Morrison, SF; Hik, DS. (2007) Demographic analysis of a declining pika Ochotona collaris population: linking survival to broad-scale climate patterns via spring snowmelt patterns.J. Anim. Ecol. 76: 899-907 Demographic analysis of a declining pika Ochotona collaris population: linking survival to broad-scale climate patterns via spring snowmelt patterns
collared pika; fertility; life-table response experiment; Pacific Decadal Oscillation; snowmelt
1. Demographic analysis is essential in order to determine which factors, such as survival, fertility and other life-history characteristics, have the greatest influence on a population's rate of growth (lambda). 2. We used life-table response experiments (LTREs) to assess the relative importance of survival and fertility rates for an alpine lagomorph, the collared pika Ochotona collaris, using 12 years (1995-2006) of census data. The LTRE analysis was repeated for each of three subpopulations within the main study site that were defined by aspect (east, west and south). 3. Across the entire study site, the survival and fertility of adults contributed 35.6 and 43.5%, respectively, to the variance observed in the projected population growth rate, V(lambda), whereas juvenile survival contributed 20.9%. Adult survival and fertility contributed approximately equal amounts for each subpopulation when considered separately, although their rank order varied spatially. 4. Adult survival across the entire site was positively correlated to the Pacific Decadal Oscillation (PDO) with a time lag of 1 year, and was uncorrelated to adult density. The PDO was negatively correlated to the timing of spring snowmelt at our site, implicating the importance of earlier spring conditions and plant phenology on the subsequent winter survival of adults and therefore, population growth. 5. When subpopulations were analysed separately, survivals and fertilities were variously correlated to lagged PDO and adult densities, but the patterns varied spatially. Therefore, the mechanisms underlying V(lambda) can vary substantially over relatively short distances. DOI
44. Noble, JC; Hik, DS; Sinclair, ARE. (2007) Landscape ecology of the burrowing bettong: fire and marsupial biocontrol of shrubs in semi-arid Australia.Rangeland J. 29: 107-119 Landscape ecology of the burrowing bettong: fire and marsupial biocontrol of shrubs in semi-arid Australia
foregut fermentation; mesomarsupials; multiple states; woodlands
Prior to European settlement, medium-sized marsupials, especially bettongs (Bettongia spp.), were widely distributed across arid and semi-arid Australia. Most disappeared rapidly in the late 1800s in the earliest settled rangelands such as the West Darling region of western New SouthWales following the spread of domestic herbivores, rabbit invasion, exotic predators and loss of habitat. Because the burrowing bettong ( Bettongia lesueur) is the only fossorial macropod species, it left a clearly visible record of its past presence, distribution and habitat preferences in the form of substantial relict warrens, particularly in stony, 'hard-red' habitats. With the reduction in. re frequency because of excessive grazing pressures following European settlement in the 19th century, there was a rapid increase in the density of unpalatable native shrubs. We examine the hypothesis that periodic wild. res and browsing by bettongs were together able to regulate shrub densities in semi-arid rangelands in Australia. Information from various sources concerning the effects of. re, rainfall and browsing on the demography of shrubs was used to construct a model of shrub population dynamics. The model indicates the potential for two states for a given bettong density: first,a low shrub density maintained by a combination of periodic. re and bettong browsing; and second, a high shrub density in the absence of fire. These results have broad implications for pastoral and conservation management in Australian semi-arid rangelands. DOI
43. Davey, C; Sinclair, ARE; Pech, RP; Arthur, AD; Krebs, CJ; Newsome, AE; Hik, D; Molsher, R; Allcock, K. (2006) Do exotic vertebrates structure the biota of Australia? An experimental test in New South Wales.Ecosystems 9: 992-1008 Do exotic vertebrates structure the biota of Australia? An experimental test in New South Wales
community structure; predator-prey interactions; predator-prey manipulation; functional response; fox removal; rabbit hemorrhagic disease; Australia
From 1993 to 2001, we conducted a series of experiments in a mixed grassland-woodland system in central New South Wales (NSW) to quantify the interactions between red foxes and their prey and competitors. Foxes were removed from two areas around the perimeter of Lake Burrendong, and data were collected from these areas and a nearby untreated area before, during, and after the period of fox control. The arrival of rabbit hemorrhagic disease (RHD) in 1996 provided an opportunity to examine the interactive effects of controlling foxes and rabbits. In this landscape, typical of central NSW, (a) the fox population was not affected by a large reduction in the abundance of rabbits, or vice versa; (b) the cat population declined in areas where foxes were removed after the large RHD-induced reduction in rabbit numbers, but there was no consistent response to the removal of foxes; (c) the abundance of some macropod species increased in response only to the combined removal of rabbits and foxes; (d) there were no consistent changes in the abundances of bird species in response to the removal of either foxes or rabbits, but there were clear habitat differences in bird species richness; and (e) there was likely to be an increase in woody plant species after the large reduction in rabbit populations by RHD. We conclude that (a) long-term field experiments (more than 3 years) are required to quantify the indirect consequences of controlling foxes and rabbits, and (b) single manipulations, such as fox control or rabbit control, are not necessarily sufficient for the conservation of remnant woodland communities in southeastern Australia. DOI
42. Koh, S; Vicari, M; Ball, JP; Rakocevic, T; Zaheer, S; Hik, DS; Bazely, DR. (2006) Rapid detection of fungal endophytes in grasses for large-scale studies.Funct. Ecol. 20: 736-742 Rapid detection of fungal endophytes in grasses for large-scale studies
endophytic fungi; Festuca spp; forensic ecology; immunoblot card; monoclonal antibodies; Neotyphodium; Pooideae
1. Standard visual screening methods for determining the qualitative and quantitative presence of fungal endophytes are too time-consuming for large-scale ecological studies. 2. We investigated whether commercially available immunoblot kits, using monoclonal antibody techniques and designed for rapid-screening of the presence of Neotyphodium endophytes in fresh samples of the pasture grasses Festuca arundinacea and Lolium perenne, could be used for Neotyphodium detection using other grasses and preserved samples. We also determined whether immunoblot kits could provide quantitative information about the amount of Neotyphodium in the grass. 3. The kits accurately detected endophyte presence in F. rubra, F. ovina, F. pratensis and F. altaica, in both preserved samples (dried and fixed), including 12-year-old stored, dried samples of F. rubra. 4. Endophytes were detected in 7-day-old seedlings of Lolium perenne, 3 days (30%) earlier than previously recognized. 5. The intensity of the coloured tissue prints on scanned immunoblot cards was significantly positively correlated with hyphal density, demonstrating a previously unrecognized accurate quantitative application. 6. These findings greatly reduce logistical barriers to large-scale field research into the broader ecological significance of Neotyphodium in temperate and arctic grasses in non-agricultural ecosystems (particularly in remote areas) and suggest potential for estimating historical infection rates using stored and herbarium specimens. DOI
41. Gillis, EA; Hik, DS; Boonstra, R; Karels, TJ; Krebs, CJ. (2005) Being high is better: effects of elevation and habitat on arctic ground squirrel demography.Oikos 108: 231-240 Being high is better: effects of elevation and habitat on arctic ground squirrel demography
We investigated the effect of local environment on the demography and population dynamics of arctic ground squirrels (Spermophilus parryii plesius) by comparing reproduction, survival, and population trends of squirrels living in low elevation boreal forest and high elevation alpine tundra sites in southwestern Yukon Territory, Canada. Contrary to the trend for most birds and mammals, reproduction was significantly lower at the lower elevation and females living at higher elevation did not delay the age at which they first reproduced. Even though survival in the boreal forest was lower in summer than in the alpine, it was higher over winter so annual adult female survival was similar between sites. Sensitivity analysis of model parameters revealed that in the forest, population growth rate (lambda) was most sensitive to small changes in adult active season survival whereas for the alpine population, lambda was most sensitive to changes in juvenile winter survival. In their respective habitats, these parameters also showed high year to year variation and thus contributed greatly to the population trends observed. Even though ground squirrels persisted in the boreal forest, the measured demographic rates indicate the forest was sink habitat (lambda<1) and may have relied on nearby grassy meadows for immigrants. In contrast, the alpine habitat maintained a ground squirrel population in the absence of immigration (lambda=1). The variation in demographic rates between ground squirrels living at high and low elevation may arise from phenotypic responses of squirrels to different habitat structure. Arctic ground squirrels rely on sight to detect predators from a safe distance, and the boreal forest, with its lower visibility and higher predator density, appears to be suboptimal habitat. DOI
40. Gillis, EA; Morrison, SF; Zazula, GD; Hik, DS. (2005) Evidence for selective caching by Arctic ground squirrels living in alpine meadows in the Yukon.Arctic 58: 354-360 Evidence for selective caching by Arctic ground squirrels living in alpine meadows in the Yukon
arctic ground squirrel; Spermophilus parryii; food caching; hoarding; Polygonum; alpine
Male arctic ground squirrels (Spermophilus parryii) rely on food they cached the previous year for the energy they need to compete for mates each spring. We collected cheek-pouch contents of arctic ground squirrels trapped during three summers (2000-02) as an indication of what squirrels cached. Among adults, both males and females carried material in their cheek pouches, but males did so more frequently than females (4.4% vs. 0.6% of,captures). Males carried material later in the summer than females, and also carried different material (seeds and rhizomes as opposed to nesting material). These differences probably reflect different purposes of cheek-pouch contents-females carried material for immediate use, whereas males carried food for caching. Only 24 of over 100 species of vascular plants growing at our alpine study site were carried, and presumably cached, by male arctic ground squirrels. The seeds or rhizomes of one species, Polygonum viviparum, were found in over 90% of cheek-pouch contents examined, even though that species grew at relatively low density and was no more common than another species in the same genus (Polygonum bistorta) that was never found in cheek-pouch contents. Collectively, this evidence indicates that males are highly selective in what species they cache. Many of the species carried by arctic ground squirrels in this study have also been found in Pleistocene fossil caches from central Yukon, indicating that food preferences of this species may have remained stable over time. DOI
37. McIntire, EJB; Hik, DS. (2005) Influences of chronic and current season grazing by collared pikas on above-ground biomass and species richness in subarctic alpine meadows.Oecologia 145: 288-297 Influences of chronic and current season grazing by collared pikas on above-ground biomass and species richness in subarctic alpine meadows
grazing history; net above-ground primary production; herbivory; Yukon; Ochotona collaris: alpine
We studied an alpine herbivory gradient established by collared pikas, a small central place foraging lagomorph, to examine the effects of multiple grazing levels on above-ground live biomass (AGB) and species richness (SR) in alpine tundra. The effects of within-season (four sampling periods), multi-season (across three summers) and longer-term dynamics (inferred from spatial location of vegetation with respect to pika haypiles) were examined. Along the grazing gradient, we found support for and against hypotheses that propose biphasic, increasing, or decreasing responses to herbivory, both in terms of AGB and SR. Our results suggest that plant-herbivore predictability is still weak. To further examine the impact of herbivory, we experimentally removed pikas using mesh exclosures placed at increasing distance from the edge of talus occupied by pikas. AGB after the second consecutive year of herbivore exclusion increased by 125% compared to control plots in highly grazed areas adjacent to talus ( <1 m). In more lightly grazed sites at distances 1-6 in from talus, AGB increased by more than 40% after pikas were removed. No differences were observed in the ungrazed sites > 6 in from talus. AGB was highest in meadow patches previously grazed by pikas compared to those with little grazing history, but this response was only observed after two seasons following release from herbivory. Grazed sites at distances of 1-6 m had the highest SR. These results indicate that multi-year measurements of growth are particularly relevant in ecosystems dominated by long-lived perennials in regions where productivity is low. Infrequent herbivore vacancies may provide local short-term release from pika grazing, thereby contributing to the persistence of productive, highly palatable vegetation. DOI
36. Pickett, KN; Hik, DS; Newsome, AE; Pech, RP. (2005) The influence of predation risk on foraging behaviour of brushtail possums in Australian woodlands.Wildl. Res. 32: 121-130 The influence of predation risk on foraging behaviour of brushtail possums in Australian woodlands
The potential effects of predation risk on common brushtail possums were investigated in south-eastern Australian woodlands. Patterns of habitat use, foraging costs using giving-up density (GUD) experiments, and indices of body condition and reproductive success were examined at eight sites in two habitat types (eucalypt- or cypress-pine-dominated stands), within three areas of different red fox abundance ( high, moderate and low fox density). In cypress-pine-dominated stands, possums travelled further on the ground, visited more feeding stations and had lower GUDs at feeders where foxes were removed than did possums in high-fox-density sites. In contrast, there was no effect of fox removal on the behaviour of possums in eucalypt-dominated stands. Fox removal also had no effect on indices of body condition and reproduction. Minor effects of microhabitat were detected with trackplot and GUD experiments, but, overall, the results suggest that habitat at the stand-level was more important. The nonlethal effects of foxes in different habitats may need to be taken into account when developing conservation strategies for native marsupials. DOI
35. Richardson, E; Stirling, I; Hik, DS. (2005) Polar bear (Ursus maritimus) maternity denning habitat in western Hudson Bay: a bottom-up approach to resource selection functions.Can. J. Zool. 83: 860-870 Polar bear (Ursus maritimus) maternity denning habitat in western Hudson Bay: a bottom-up approach to resource selection functions
We examined habitat characteristics of 101 polar bear (Ursus maritimus Phipps, 1774) den sites and 83 adjacent unoccupied sites in western Hudson Bay, Canada, between mid-August and early October 2001 and 2002. Bears denned almost exclusively in peat banks (n = 100) along the edges of creeks, rivers, and lakes adjacent to open lichen tundra sites. Den sites differed from unoccupied sites by having greater tree cover (P = 0.002), less moss cover (P < 0.001), and less herbaceous cover (P = 0.005). The presence of tree roots improved substrate stability, providing support to den structures. Den entrance azimuths were weighted toward a southeasterly aspect (P < 0.005), away from the prevailing northwest winds. To identify habitats with the greatest relative probability of having a den, a resource selection function (RSF) model was developed using remote sensing imagery and 1245 known den locations. High normalized difference vegetation index and brightness values derived from Landsat imagery, which were in close proximity to water, corresponded well with polar bear den sites. Identification of critical denning areas through the use of RSF will provide resource managers with a valuable tool for ensuring the protection of denning habitat, and consequently female bears and their young. DOI
34. Allcock, KG; Hik, DS. (2004) Survival, growth, and escape from herbivory are determined by habitat and herbivore species for three Australian woodland plants.Oecologia 138: 231-241 Survival, growth, and escape from herbivory are determined by habitat and herbivore species for three Australian woodland plants
Callitris glaucophylla; Eucalyptus albens; stage-based matrix models; Themeda australis; woodland restoration
To understand how plant communities are structured by herbivory it is essential to investigate the roles of different herbivores and the responses of a variety of plant species in different habitats. We examined the effects of mammalian herbivores on survival and growth of transplanted seedlings of two native trees (Eucalyptus albens and Callitris glaucophylla), and one native grass (Themeda australis) in white box (E. albens) woodlands in eastern Australia over 3 years. Herbivores were manipulated using four fencing treatments that successively excluded livestock, macropods, and rabbits from woodland and grassland (cleared pasture). Survival was highest in the absence of mammalian herbivores and in woodlands, and patterns differed among plant species. Survival of T. australis was low, especially in grasslands, and mortality by overgrowth was common in ungrazed treatments. All plant species were taller in fenced plots, and differences between treatments were greater in grassland. Rabbits and livestock had the greatest influence on C. glaucophylla, while T. australis and E. albens were most affected by livestock and macropods. We used field data to parameterize stage-classified matrix models to predict escape from herbivory (escape height >100 cm) for tree species. Reduced herbivory increased the proportion of individuals reaching escape height after 15 years. Rate of escape was greater in grassland, and this faster growth appeared to counteract much of the negative impact of herbivores. While T. australis was unable to escape herbivory, larger, ungrazed individuals were more likely to flower and therefore contribute to the maintenance of the population. Our results show that habitat and herbivore species strongly influence the effect of herbivory on vegetation. DOI
32. Frame, PF; Hik, DS; Cluff, HD; Paquet, PC. (2004) Long foraging movement of a Denning Tundra Wolf.Arctic 57: 196-203 Long foraging movement of a Denning Tundra Wolf
wolf; GPS tracking; movements; Canis lupus; foraging; caribou; Northwest Territories
Wolves (Canis lupus) on the Canadian barrens are intimately linked to migrating herds of barren-ground caribou (Rangifer tarandus). We deployed a Global Positioning System (GPS) radio collar on an adult female wolf to record her movements in response to changing caribou densities near her den during summer. This wolf and two other females were observed nursing a group of I I pups. She traveled a minimum of 341 km during a 14-day excursion. The straight-line distance from the den to the farthest location was 103 km, and the overall minimum rate of travel was 3.1 km/h. The distance between the wolf and the radio-collared caribou decreased from 242 km one week before the excursion to 8 km four days into the excursion. We discuss several possible explanations for the long foraging bout.
31. Franken, RJ; Hik, DS. (2004) Influence of habitat quality, patch size and connectivity on colonization and extinction dynamics of collared pikas Ochotona collaris.J. Anim. Ecol. 73: 889-896 Influence of habitat quality, patch size and connectivity on colonization and extinction dynamics of collared pikas Ochotona collaris
area; isolation; metapopulation; occupancy; persistence
1. The effects of habitat quality, patch size and connectivity between patches on patterns of local extinction and colonization of collared pikas were studied over 7 years in alpine meadows in the south-west Yukon. 2. Although adult population size independently had a significant influence on patch extinction, its influence was minimal when other variables were included in generalized linear models. Instead, an index of habitat quality and the connectivity of a patch were found to be the best predictors of pika extinction. 3. Similarly, patch connectivity only partly explained the recolonization of talus patches by pikas. Other patch characteristics, including aspect, amount of vegetation within the patch and an index of habitat quality based on survival probability of pikas also had a significant influence on recolonization. 4. These results suggest that the influence of patch quality on local extinction and recolonization need to be more fully incorporated into metapopulation models. DOI
30. Franken, RJ; Hik, DS. (2004) Interannual variation in timing of parturition and growth of collared pikas (Ochotona collaris) in the southwest Yukon.Integr. Comp. Biol. 44: 186-193 Interannual variation in timing of parturition and growth of collared pikas (Ochotona collaris) in the southwest Yukon
The length of the snow-free season has a significant influence on reproduction and growth in northern alpine environments, and these life history traits may provide sensitive indicators of the responses of organisms to climate change. We examined growth rates and timing of parturition of collared pikas (Ochotona collaris) from 1995-2002 in the Ruby Range, Yukon Territory, Canada. Growth rates were best described using a Gompertz model, in which the asymptotic mass, determined from the average male and female weights, was 157 g, the growth rate constant (K) was 0.0557, and the age at inflection (1) was 18.12 days, for a birth weight of 10 g. The maximum growth rate for North American pikas (O. collaris and O. princeps) increased with latitude, with maximum growth rates being approximately one-third greater in northern populations where the snow-free season is less than three months long. The mean parturition date varied significantly among years from 3 June to 3 July, and delayed parturition was correlated with indices of high snow accumulation and, to a lesser extent, late spring snowmelt. However, parturition date did not significantly affect the subsequent over-winter survival of juveniles in this population, suggesting that pikas are able to adjust to seasonal uncertainty associated with highly variable spring conditions. DOI
27. Karels, TJ; Bryant, AA; Hik, DS. (2004) Comparison of discriminant function and classification tree analyses for age classification of marmots.Oikos 105: 575-587 Comparison of discriminant function and classification tree analyses for age classification of marmots
We evaluated the predictive power of two classification techniques, one parametric - discriminant function analysis (DFA) and the other non-parametric - classification and regression tree analysis (CART), in order to provide a non-subjective quantitative method of determining age class in Vancouver Island marmots (Marmota vancouverensis) and hoary marmots (Marmota caligata). For both techniques we used morphological measurements of known-age male and female marmots from two independent population studies to build and test predictive models of age class. Both techniques had high predictive power (69-86%) for both sexes and both species. Overall, the two methods performed identically with 81% correct classification. DFA was marginally better at discriminating among older more challenging age classes compared to CART. However, in our test samples, cases with missing values in any of the discriminant variables were deleted and hence unclassified by DFA, whereas CART used values from closely correlated variables to substitute for the missing values. Therefore, overall, CART performed better (CART 81% vs DFA 76%) because of its ability to classify incomplete cases. Correct classification rates were approximately 10% higher for hoary marmots than for Vancouver Island marmots, a result that could be attributed to different sets of morphological measurements. Zygomatic arch breadth measured in hoary marmots was the most important predictor of age class in both sexes using both classification techniques. We recommend that CART analysis be performed on data-sets with incomplete records and used as a variable screening tool prior to DFA on more complete data-sets. DOI
26. Karels, TJ; Koppel, L; Hik, DS. (2004) Fecal pellet counts as a technique for monitoring an alpine-dwelling social rodent, the hoary marmot (Marmota caligata).Arct. Antarct. Alp. Res. 36: 490-494 Fecal pellet counts as a technique for monitoring an alpine-dwelling social rodent, the hoary marmot (Marmota caligata)
alpine
We evaluated fecal pellet counts as an index of hoary marmot (Marmota caligata) social group size in order to develop a simple, inexpensive method for monitoring population change of a widely distributed, but poorly studied alpine mammal. Fecal pellet counts were conducted in three separate seasons along several 2 in X 100 in transects located parallel to and 10, 20, and 30 in from the edge of alpine boulderfields (talus) occupied by marmots. Marmot activity and location relative to talus was also determined to assess the proportion of time spent foraging as a function of distance from refuge. Marmots spent 74% of their activities in meadows at a mean distance of 11.6 in from talus, and activity in meadows declined with increasing distance from talus, as did fecal pellet counts. Fecal counts at 10 in from the edge of talus were strongly and linearly related (r(2) = 0.89) to marmot abundance. The functional equation of marmot abundance predicted marmot abundance in five independent social groups within 17% of the observed group size. Fecal pellet counts appear to provide a precise index of marmot group size suitable for long-term monitoring of population change. DOI
25. Kyle, CJ; Karels, TJ; Clark, B; Strobeck, C; Hik, DS; Davis, CS. (2004) Isolation and characterization of microsatellite markers in hoary marmots (Marmota caligata).Mol. Ecol. Notes 4: 749-751 Isolation and characterization of microsatellite markers in hoary marmots (Marmota caligata)
hoary marmot; Marmota caligata; mating system; microsatellite; parentage; Scuiridae
Microsatellite loci were developed from hoary marmots (Marmota caligata) to aid in the investigation of the social structure and mating system of this species. Seven of the microsatellite loci developed were found to be moderately polymorphic with between two and seven alleles per locus. In addition to the microsatellites developed in hoary marmots we also tested markers developed for other scuirids, namely European alpine marmots (M. marmota), Columbian ground squirrels (Spermophilus columbianus) and European ground squirrels (S. citellus). Of these markers, 13 were polymorphic when amplified in hoary marmots with between two and nine alleles per locus. DOI
24. Morrison, S; Barton, L; Caputa, P; Hik, DS. (2004) Forage selection by collared pikas, Ochotona collaris, under varying degrees of predation risk.Can. J. Zool.-Rev. Can. Zool. 82: 533-540 Forage selection by collared pikas, Ochotona collaris, under varying degrees of predation risk
The effects of predation risk on foraging behavior often result in a trade-off between obtaining food and seeking shelter and may alter the selectivity of herbivores for individual plant species. We experimentally measured forage selection by a small alpine herbivore, the collared pika (Ochotona collaris (Nelson, 1893)), using a cafeteria-style arrangement of six potential forage species at five levels of predation risk. Contrary to our prediction, haying pikas did not switch preferences for forage species of different nutritional quality as predation risk increased. However, the total amount of forage removed was inversely related to risk, and the addition of cover at treatments of greatest potential risk ameliorated the negative effects of higher predation risk. The reasons for increased preference for poorer quality forage species in 2002 relative to 2000 are currently unknown but may reflect changes in predator abundance, forage quality, or increased competition for limited forage resources. DOI
23. Allcock, KG; Hik, DS. (2003) What determines disturbance-productivity-diversity relationships? The effect of scale, species and environment on richness patterns in an Australian woodland.Oikos 102: 173-185 What determines disturbance-productivity-diversity relationships? The effect of scale, species and environment on richness patterns in an Australian woodland
Much of the observed variation in relationships between diversity and disturbance or productivity may be attributed to scale, species characteristics, or environment. We used exclusion fences to create gradients of grazing (by native and introduced herbivores), cover, and standing crop in temperate Eucalypt woodlands. We investigated patterns of native, exotic, and total plant species richness at two scales (1 m(2) and 625 m(2)). Richness patterns were similar at both scales, though species richness at 1m(2) was more strongly affected by our grazing treatments. Season and rainfall explained more variation in richness than did surrogate measures of productivity or disturbance by herbivores. The richness-herbivory relationship depended strongly on rainfall, season, and species origin, and altering these factors produced the entire range of observed diversity-disturbance relationships. Richness-biomass and richness-cover relationships were consistently hump-shaped, and related to species origin with native richness negatively related and exotic richness positively related. The ability of weedy annuals to pre-empt space after death may have contributed to the observed unimodal responses. DOI
22. Danby, RK; Hik, DS; Slocombe, DS; Williams, A. (2003) Science and the St Elias: an evolving framework for sustainability in North America's highest mountains.Geogr. J. 169: 191-204 Science and the St Elias: an evolving framework for sustainability in North America's highest mountains
Yukon; St Elias Mountains; Kluane National Park Reserve; science history; traditional knowledge; regional development; ecosystem-based management
The past, present, and future contributions of science in the St Elias Mountains, and its relationship with regional development, resource management, and traditional ecological knowledge is examined. Science has evolved from an early foundation of exploration, through stages of resource inventories and surveys, to deductive scientific research and, more recently, a promising reconnection with traditional knowledge. Directly and indirectly, events such as the Klondike Gold Rush, construction of the Alaska Highway, creation of the Arctic Institute of North America's Kluane Lake Research Station, and establishment of protected areas have helped foster scientific activities in the region. In turn, this scientific perspective has influenced regional development by providing detailed information that has been utilized, to varying degrees, in resource use, planning, and decisionmaking. Over the past decade, management of the region has become less sectoral and more cooperative in nature, due partly to the implementation of co-management agreements, regional land use planning, and settlement of first nations' land claims. Incorporating both science and traditional knowledge into this process through collaborative endeavours such as long-term ecological monitoring, adaptive management, and information integration will contribute to ecosystem-based management of the St Elias and ensure that both perspectives play an integral role in sustainable development of the region. DOI
21.Hik, DS; Brown, M; Dabros, A; Weir, J; Cahill, JF. (2003) Prevalence and predictability of handling effects in field studies: Results from field experiments and a meta-analysis.Am. J. Bot. 90: 270-277 Prevalence and predictability of handling effects in field studies: Results from field experiments and a meta-analysis
alpine meadow; boreal forest; grassland; meta-analysis; observer effect; old field; thigmomorphogenesis; visitation
Various effects on plant growth associated with handling or touching plants are well documented from greenhouse and laboratory studies, but are generally unknown or ignored under field conditions. We examined the prevalence of the effects of handling, at levels typical of many ecological experiments, on aboveground biomass and damage by invertebrate herbivores for a total of 16 common species from three plant communities in western Canada. Significant effects of handling were observed in the alpine meadow and grassland, but not in the boreal forest. Handling reduced aboveground biomass and increased the mean intensity of invertebrate leaf damage for most species. A meta-analysis of the relationship between plant traits and response to handling indicated that woody plants and species without strong chemical or conspicuous morphological defenses were most strongly affected. Overall, our results indicate that potentially confounding effects of routinely sampling plants in the field are widespread and merit further investigation. DOI
20. Tait, MA; Hik, DS. (2003) Is dimethylsulfoxide a reliable solvent for extracting chlorophyll under field conditions?Photosynth. Res. 78: 87-91 Is dimethylsulfoxide a reliable solvent for extracting chlorophyll under field conditions?
acetone; chlorophyll extraction; dimethylsulfoxide; DMSO; field methodology
Dimethylsulfoxide ( DMSO) appears to be a reliable solvent for extracting chlorophyll (Chl), however, modification of standard methods may be necessary for some species under field conditions. We found that Chl extraction of whole leaf tissue with DMSO incubated at between 25 and 40 degreesC was generally similar to the 80% acetone method, except for one graminoid species that required maceration. There was little effect of incubation temperature or duration of incubation beyond 7 h on extraction efficiency, but DMSO extracts were less stable than acetone extracts during one week of cold storage, especially if they thawed during this period. Since Chl extraction methods may provide variable results, particularly in the field, studies using different solvents should be compared cautiously unless specific methods have been calibrated. DOI
18. Mcintire, EJB; Hik, DS. (2002) Grazing history versus current grazing: leaf demography and compensatory growth of three alpine plants in response to a native herbivore (Ochotona collaris).J. Ecol. 90: 348-359 Grazing history versus current grazing: leaf demography and compensatory growth of three alpine plants in response to a native herbivore (Ochotona collaris)
alpine meadows; collared pika; Erigeron humilis; grazing history; herbivory gradient; Kobresia myosuroides; Ochotona collaris; Oxytropis nigrescens
1 We measured leaf births, leaf deaths and leaf length of three alpine perennial species, Kobresia myosuroides, Erigeron humilis and Oxytropis nigrescens, from sites with different grazing histories (strong or weak) in response to two levels of current season grazing (present or absent) by collared pikas (Ochotona collaris), a small lagomorph, in the south-west Yukon. 2 All three species appeared to tolerate the removal of 58-61% of summer leaf production under natural conditions. Grazing history, which was defined by the location of plants located either < 2 m or > 6 m from boulderfields with a history of occupation by pikas, was the most significant factor determining shifts in leaf births and leaf deaths following herbivory. 3 The only detectable influence of current season herbivory for any measured species was a reduction of leaf length of Kobresia. 4 A comparison of historically grazed with historically ungrazed plants indicated several changes in leaf demography and morphology. Kobresia leaves were generally shorter and had higher rates of production of new leaves. Oxytropis had higher rates of new leaf production. Erigeron had fewer leaf births throughout the summer, but showed a large and highly significant delay in the timing of leaf senescence. 5 These responses can be largely understood as strategies to avoid the predictable intensive late season foraging that is characteristic of pikas. Morphological mechanisms allow these species to tolerate and, more importantly for the herbivore, persist under heavy and chronic grazing. DOI
17. Cornelissen, JHC; Callaghan, TV; Alatalo, JM; Michelsen, A; Graglia, E; Hartley, AE; Hik, DS; Hobbie, SE; Press, MC; Robinson, CH; Henry, GHR; Shaver, GR; Phoenix, GK; Jones, DG; Jonasson, S; Chapin, FS; Molau, U; Neill, C; Lee, JA; Melillo, JM; Sveinbjornsson, B; Aerts, R. (2001) Global change and arctic ecosystems: is lichen decline a function of increases in vascular plant biomass?J. Ecol. 89: 984-994 Global change and arctic ecosystems: is lichen decline a function of increases in vascular plant biomass?
arctic; ecosystem manipulation experiment; macrolichen; nutrient availability; vascular plant; warming
1 Macrolichens are important for the functioning and biodiversity of cold northern ecosystems and their reindeer-based cultures and economics. 2 We hypothesized that, in climatically milder parts of the Arctic, where ecosystems have relatively dense plant canopies, climate warming and/or increased nutrient availability leads to decline in macrolichen abundance as a function of increased abundance of vascular plants. In more open high-arctic or arctic-alpine plant communities such a relationship should be absent. To test this, we synthesized cross-continental arctic vegetation data from ecosystem manipulation experiments simulating mostly warming and increased nutrient availability, and compared these with similar data from natural environmental gradients. 3 Regressions between abundance or biomass of macrolichens and vascular plants were consistently negative across the subarctic and mid-arctic experimental studies. Such a pattern did not emerge in the coldest high-arctic or arctic-alpine sites. The slopes of the negative regressions increased across 10 sites as the climate became milder (as indicated by a simple climatic index) or the vegetation denser (greater site above-ground biomass). 4 Seven natural vegetation gradients in the lower-altitude sub- and mid-arctic zone confirmed the patterns seen in the experimental studies, showing consistent negative relationships between abundance of macrolichens and vascular plants. 5 We conclude that the data supported the hypothesis. Macrolichens in climatically milder arctic ecosystems may decline if and where global changes cause vascular plants to increase in abundance. 6 However, a refining of our findings is needed, for instance by integrating other abiotic and biotic effects such as reindeer grazing feedback on the balance between vascular plants and lichens. DOI
16.Hik, DS; McColl, CJ; Boonstra, R. (2001) Why are Arctic ground squirrels more stressed in the boreal forest than in alpine meadows?Ecoscience 8: 275-288 Why are Arctic ground squirrels more stressed in the boreal forest than in alpine meadows?
Arctic ground squirrels; hypothalamic-pituitary-adrenal axis; predation risk; stress; sublethal effects: alpine
Arctic ground squirrels (Spermophilus parryii plesius Richardson) in the southeastern Yukon live in both boreal forest and alpine tundra habitats. We live-trapped young male and female squirrels in both habitat types and subjected them to a standardized hormonal-challenge protocol to assess the responsiveness of their hypothalamic-pituitary-adrenal axis. Alpine squirrels had levels of free cortisol at the baseline (initial) bleed following their removal from traps that were 3 times higher in males and 5 times higher in females compared with boreal forest squirrels. Females, but not males, from the boreal forest were dexamethasone resistant, while neither sex from the alpine habitat was resistant. Free cortisol in alpine squirrels also responded more dramatically after the injection of adrenocorticotropic hormone. Corticosteroid-binding globulin levels were significantly lower in forest than alpine squirrels and these levels were not markedly affected by the challenge protocol. Glucose levels were significantly higher in boreal than alpine squirrels and the pattern differed between the two sites in response to the protocol. Hematocrits were significantly higher in alpine squirrels. Collectively, this evidence suggests that Arctic ground squirrels were more chronically stressed in the boreal forest than in the alpine meadows. The most likely explanation for our results is higher predation risk in the forest compared with alpine meadows, as, forage availability and population density were not significantly different between the two habitats. DOI
14. Boonstra, R; Hik, D; Singleton, GR; Tinnikov, A. (1998) The impact of predator-induced stress on the snowshoe hare cycle.Ecol. Monogr. 68: 371-394 The impact of predator-induced stress on the snowshoe hare cycle
corticosteroid-binding globulin; cortisol; field endocrinology; cycles; population; gluconeogenesis and glucose metabolism; hypothalamic-pituitary-adrenal axis immunosuppression; predation risk; snowshoe hare cycles; stress; chronic; sublethal effects; Yukon (Canada)
The sublethal effects of high predation risk on both prey behavior and physiology may have long-term consequences for prey population dynamics. We tested the hypothesis that snowshoe hares during the population decline are chronically stressed because of high predation risk whereas those during the population low are not, and that this has negative effects on both their physiology and demography. Snowshoe hares exhibit 10-yr population cycles; during declines, virtually every hare that dies is killed by a predator. We assessed the physiological responsiveness of the stress axis and of energy mobilization by subjecting hares during the population decline and low to a hormonal-challenge protocol. We monitored the population demography through live-trapping and assessed reproduction through a maternal-cage technique. During the 1990s' decline in the Yukon, Canada, hares were chronically stressed-as indicated by higher levels of free cortisol, reduced maximum corticosteroid-binding capacity, reduced testosterone response, reduced index of body condition, reduced leucocyte counts, increased overwinter body-mass loss, and increased glucose mobilization, relative to hares during the population low. This evidence is consistent with the explanation that predation risk, not high hare density or poor nutritional condition, accounted for the chronic stress and for the marked deterioration of reproduction during the decline. Reproduction and indices of stress physiology did not improve until predation risk declined. These findings may also account for the lag in recovery of hare reproduction after predator densities have declined and thus may implicate the long-term consequences of predation risk on prey populations beyond the immediate effects of predators on prey behavior and physiology. DOI
13. Sinclair, ARE; Pech, RP; Dickman, CR; Hik, D; Mahon, P; Newsome, AE. (1998) Predicting effects of predation on conservation of endangered prey.Conserv. Biol. 12: 564-575 Predicting effects of predation on conservation of endangered prey
In parts of the world such as the Pacific Islands, Australia, and New Zealand,introduced vertebrate predators have caused the demise of indigenous mammal and bird species. A number of releases for reestablishment of these mammal species in mainland Australia have failed because predators extirpated the new populations. The nature of the decline of both extant populations and reintroduced colonies provides information on the dynamics of predation. Predator-prey theory suggests that the effects of predation are usually inversely dependent on density (depensatory) when the prey are not the primary food supply of exotic predators. Thus, such predators can cause extinction of endemic prey species. Three types of evidence can be deduced from the predator-prey interactions that allow predictions for conservation: (1) whether per capital rates of change for prey increase or decrease with declining prey densities, (2) whether predation is depensatory or density-dependent, and (3) the overall magnitude of predation. If this magnitude is too high for coexistence, then the degree of predator removal required can be predicted. If the magnitude of predation is sufficiently low, then the threshold density of prey that management must achieve to allow predator and prey to coexist can also be predicted. We analyzed published reports of both declining populations and reintroduced colonies of endangered marsupial populations in Australia. The observed predation curves conformed to the predictions of predator-prey theory. Some, such as the black-footed rock-wallaby (Petrogale lateralis), were classic alternate prey and were vulnerable below a threshold population size. Others, such as the brush-tailed bettong (Bettongia penicillata), have a refuge at low numbers and thus offer the best chance for reintroduction. Our predictions suggest a protocol for an experimental management program for the conservation of sensitive prey species: (1) determination of net rates of change of prey with declining population, (2) improvement of survivorship through habitat manipulation, (3) improvement of survivorship through predator removal, (4) determination of the threshold density above which reintroductions can succeed, and (5) manipulations to change interactions form Type II to Type III. The task in the future is to determine how to change the vulnerability of the prey so that they can have a refuge at low numbers. DOI
12. HIK, DS. (1995) DOES RISK OF PREDATION INFLUENCE POPULATION-DYNAMICS - EVIDENCE FROM THE CYCLIC DECLINE OF SNOWSHOE HARES.Wildl. Res. 22: 115-129 DOES RISK OF PREDATION INFLUENCE POPULATION-DYNAMICS - EVIDENCE FROM THE CYCLIC DECLINE OF SNOWSHOE HARES
Like most heavily preyed-upon animals, snowshoe hares (Lepus americanus) have to balance conflicting demands of obtaining food at a high rate and avoiding predators. Adopting foraging behaviours to minimise predation risk may also lead to a decline in condition, and hence fecundity. Predictions of three hypotheses (condition constraint hypothesis, predator-avoidance constraint hypothesis, predation-sensitive foraging (PSF) hypothesis) were tested by comparing changes in the survival and condition of snowshoe hares on four experimental areas in winter during a cyclic peak and decline (1989-1993) near Kluane Lake, Yukon, Canada, where (i) predation risk was reduced by excluding terrestrial predators (FENCE), (ii) food supply was supplemented with rabbit chow ad libitum (FOOD), (iii) these two treatments were combined (FENCE+FOOD), and (iv) an unmanipulated CONTROL was used. Different patterns of survival and changes in body mass were observed in the presence and absence of terrestrial predators. On the CONTROL area, female body mass and fecundity declined, even though sufficient winter forage was apparently available in all years. A similar decrease in body mass was observed on the FOOD treatment, but only during the third year of the population decline. In contrast, female body mass remained high throughout the decline in the absence of terrestrial predators in the FENCE+FOOD and FENCE treatments. Winter survival declined on CONTROL and FENCE areas during the first year of the population decline (1991), but remained higher on FOOD until 1992 and FENCE+FOOD until 1993. These results generally supported the PSF hypothesis where terrestrial predators were present (CONTROL and FOOD grids). Where terrestrial predators were absent (FENCE and FENCE+FOOD), the results supported the alternative condition constraint hypothesis. The evidence suggests that a cascade of sublethal behavioural and physiological effects associated with increased predation risk contribute to the population decline and delayed recovery of cyclic low-phase populations of snowshoe hares. DOI
11. SINCLAIR, ARE; HIK, DS; SCHMITZ, OJ; SCUDDER, GGE; TURPIN, DH; LARTER, NC. (1995) BIODIVERSITY AND THE NEED FOR HABITAT RENEWAL.Ecol. Appl. 5: 579-587 BIODIVERSITY AND THE NEED FOR HABITAT RENEWAL
BIODIVERSITY; BIOLOGICAL RESERVES; CONSERVATION; HABITAT AS RENEWABLE RESOURCE; HABITAT CONSTANT; HABITAT DECAY; HABITAT PRESERVATION; HABITAT RENEWAL
The conservation of species requires preservation of natural habitats. Where the integrity of natural habitats has been upset, species go extinct. All natural habitats are continuing to decline, both inside and outside of reserves. Habitat change is partly a natural process (e.g., succession), but human activities have accelerated the process of decay so that natural rates of renewal are insufficient to maintain natural habitats. We argue that our only recourse, in light of these scenarios, is to adopt a new conservation strategy that considers the importance of habitat renewal in addition to habitat preservation. Accordingly, in our management decisions we must not only choose the size of area to preserve but also the size of area that balances habitat loss with habitat renewal. We also suggest that this habitat equilibrium point, H*, needs to be decided upon urgently, otherwise many species will become extinct in the next 50 yr according to numerous predictions. There are two ways to achieve H*. The first is to set habitats aside in protected areas in perpetuity. There are two reasons why this protection alone is insufficient: (1) protected areas continue to decline, albeit at a slower rate than outside of their boundaries, and (2) achieving H* simply by setting aside protected areas is no longer an option in many areas where severe habitat degradation or fragmentation has already occurred. The other way to achieve H* is to promote the restablishment of natural habitats, or ''habitat renewal.'' This concept is illustrated using a simple trade-off model that balances habitat decay and habitat renewal. We then provide examples of habitat loss outside and inside of protected areas and discuss the potential for habitat renewal to offset these losses. We conclude that continued emphasis needs to be placed on setting aside natural habitat in protected areas. However, our examples of habitat loss show that this policy alone is most likely doomed to failure, so a policy of habitat renewal is also required. DOI
10. ZELLMER, ID; CLAUSS, MJ; HIK, DS; JEFFERIES, RL. (1993) GROWTH-RESPONSES OF ARCTIC GRAMINOIDS FOLLOWING GRAZING BY CAPTIVE LESSER SNOW GEESE.Oecologia 93: 487-492 GROWTH-RESPONSES OF ARCTIC GRAMINOIDS FOLLOWING GRAZING BY CAPTIVE LESSER SNOW GEESE
LESSER SNOW GEESE; ARCTIC COASTAL GRAMINOIDS; HERBIVORY; GROWTH OF FORAGE SPECIES
The effects of grazing by captive goslings of the Lesser Snow Goose on coastal vegetation at La Perouse By, Manitoba were investigated. Swards of Carex subspathacea, Festuca rubra and Calamagrostis deschampsioides were grazed once for different periods (0-180 min) and regrowth of vegetation determined, based on measurements of standing crop, net above-ground primary production (NAPP) and forage quality (leaf nitrogen content). The amounts of foliage removed from swards of Carex subspathacea increased with the length of the grazing period, but after 44 days of regrowth there were no significant differences in above-ground biomass between control and grazed plots. While the amount of foliage removed by goslings from swards of Festuca rubra increased with the length of the grazing period (except after 150 min of grazing), the increase in biomass following defoliation was similar among treatments. Goslings removed little biomass from swards of Calamagrostis deschampsioides, even when the opportunity for grazing was 180 min. No significant differences in standing-crop or NAPP between grazed and ungrazed plots were detected by the end of summer. Grazing had no significant effect on amounts of nitrogen in leaf tissue of all species, suggesting that faecal nitrogen was not rapidly incorporated into plant biomass within the growing season. Patterns of regrowth of these species are compared to that of Puccinellia phryganodes. An increase in goose numbers in recent years has led to birds foraging on less preferred species, such as Calamagrostis deschampsiodes and Festuca rubra. Their poor nutritional quality and a lack of a rapid growth response following defoliation may explain, in part, the decline in the weight of wild goslings recorded over the last decade. DOI
9. HIK, DS; JEFFERIES, RL; SINCLAIR, ARE. (1992) FORAGING BY GEESE, ISOSTATIC UPLIFT AND ASYMMETRY IN THE DEVELOPMENT OF SALT-MARSH PLANT-COMMUNITIES.J. Ecol. 80: 395-406 FORAGING BY GEESE, ISOSTATIC UPLIFT AND ASYMMETRY IN THE DEVELOPMENT OF SALT-MARSH PLANT-COMMUNITIES
ARCTIC SALT-MARSHES; EDAPHIC PROCESSES; GRAZING LAWNS; LESSER SNOW GOOSE; MULTIPLE-STATE COMMUNITIES
1. The response of different salt-marsh plant communities to grazing by lesser snow geese and isostatic uplift was examined at La Perouse Bay, Manitoba on the Hudson Bay coast. Results are based on direct experimental manipulation of swards and previously published floristic and biomass data. 2. At the seaward end of the salt-marsh the vegetation is composed of Puccinellia phryganodes and Carex subspathacea. This assemblage of species is also present in the upper marsh, but only as a consequence of intense grazing by geese. Grazed swards of these species persist over a period of at least 10 years. 3. When swards are protected from grazing in the upper marsh, rapid changes in floristic composition of vegetation occur. There is a substantial increase in above-ground biomass and the vegetation is dominated by Calamagrostis deschampsiodes, Festuca rubra and dicotyledonous plants. When these swards are grazed the species composition does not revert to the Puccinellia-Carex assemblage. 4. In the presence of grazing this change from the Puccinellia-Carex assemblage to the Calamagrostis-Festuca assemblage occurs gradually as a consequence of changes in edaphic conditions associated with isostatic uplift. The geese delay the rate of vegetational development associated with the effects of isostatic uplift but they cannot arrest it. 5. Both types of plant assemblage may become extinct locally as a result of grubbing by the geese for roots and rhizomes of graminoid species. Habitat conditions are sufficiently altered following grubbing that the process of succession recommences from bare sediment. 6. The results of changes in floristic composition, above-ground biomass and replacement rates of vegetation are examined in relation to predictions of multiple-state models which emphasize the directional asymmetry in the development of plant communities. DOI
8. MARTIN, K; HIK, D. (1992) WILLOW PTARMIGAN CHICKS CONSUME MOSS SPOROPHYTE CAPSULES.J. Field Ornithol. 63: 355-358 WILLOW PTARMIGAN CHICKS CONSUME MOSS SPOROPHYTE CAPSULES
Willow Ptarmigan (Lagopus lagopus) chicks consumed sporophyte capsules of a moss, Distichium inclinatum, at La Perouse Bay, near Churchill, Manitoba, Canada. Six chicks (6-16 d old) were examined over 3 yr, and crops of all chicks contained moss capsules. In two chicks, capsules represented a substantial proportion of the total crop contents. Crops contained little animal matter. Moss sporophyte capsules may provide an easily accessible forage for rapidly growing grouse chicks of northern populations.
7. SCHMITZ, OJ; HIK, DS; SINCLAIR, ARE. (1992) PLANT-CHEMICAL DEFENSE AND TWIG SELECTION BY SNOWSHOE HARE - AN OPTIMAL FORAGING PERSPECTIVE.Oikos 65: 295-300 PLANT-CHEMICAL DEFENSE AND TWIG SELECTION BY SNOWSHOE HARE - AN OPTIMAL FORAGING PERSPECTIVE
We examined preferences of snowshoe hares for twigs of 2 winter forage plants: chemically defended balsam poplar Populus balsamifera and comparatively less defended gray willow Salix glauca. We used an optimal foraging model that explicitly incorporates the effects of secondary plant chemicals to predict foraging preferences of hares. The model predicted that the foraging preferences should be conditional: preference should depend on the ratio of digestible nutrient content in the defended and comparatively less defended plants relative to the ratio of the wet mass/dry mass of defended and comparatively less defended plants. We conducted a feeding experiment in which we presented hares fresh twigs of P. balsamifera and S. glauca (controls). We also manipulated the wet mass/dry mass ratio and nutrient contents of P. balsamifera and S. glauca twigs to alter the above condition. (1) Drying the P. balsamifera twigs, to reduce their wet mass/dry mass ratio, resulted in a two fold increase in their consumption while the consumption of the undried, S. glauca remained similar to control levels. The efficacy of the plant defense was predictably reduced. (2) Consistent with model predictions, we reversed this behavior by presenting hares with dried twigs of both species. In this case, consumption did not differ from control levels indicating the defense was again effective. (3) The defense was also rendered less effective against hare browsing by increasing the nitrogen content of P. balsamifera twigs. It appears that hares do not exclusively select twigs to maximize the intake of a limiting nutrient or avoid plants containing secondary compounds. Preference is conditional upon the relative nutritional, physical and chemical attributes of highly defended and less defended browse species available in a habitat. DOI
6. HIK, DS; SADUL, HA; JEFFERIES, RL. (1991) EFFECTS OF THE TIMING OF MULTIPLE GRAZINGS BY GEESE ON NET ABOVEGROUND PRIMARY PRODUCTION OF SWARDS OF PUCCINELLIA-PHRYGANODES.J. Ecol. 79: 715-730 EFFECTS OF THE TIMING OF MULTIPLE GRAZINGS BY GEESE ON NET ABOVEGROUND PRIMARY PRODUCTION OF SWARDS OF PUCCINELLIA-PHRYGANODES
(1) The effects of the frequency and timing of multiple grazings (including faecal input) by captive goslings of the lesser snow goose on net above-ground primary production (NAPP) and shoot nitrogen content of swards of the forage grass, Puccinellia phryganodes were examined. The effects of clipping and addition of nitrogen on the growth in pots of individual tillers of this grass were also investigated in a factorial experiment designed to separate the effects of each treatment. The experimental design of both investigations was closely based on the foraging behaviour of wild geese on Puccinellia swards. (2) The clipping of leaves per se which mimicked the leaf demography of shoots grazed by wild birds had a detrimental effect on shoot growth and NAPP. Addition of nutrients ameliorated the adverse effects of clipping on shoot growth. Plants which received nutrients, but whose leaves were not clipped, produced the highest amount of above-ground biomass. (3) During the summer of 1987 plots of Puccinellia were either grazed once every 12 days (one to six occasions), or once every 24 days (two or three occasions), or on three occasions at intervals of 12 days late in the season after the wild geese had left the marsh. Plots grazed on three occasions at intervals of 12 days from late June to early August during the period of rapid growth of above-ground biomass most closely mimicked the foraging behaviour of the wild geese. (4) Seasonal cumulative NAPP in 1987 was significantly higher in plots grazed on three occasions than in ungrazed plots, plots grazed once, or plots grazed repeatedly throughout the season. In 1988 plots were not grazed and a similar trend in NAPP was obtained, except that the NAPP of plots grazed late in the season in 1987 was low. The departure of wild geese in early August may be necessary if swards are to recover from the effects of defoliation. (5) During the summer of 1987, forage quality (N content) and NAPP together were highest in plots grazed on three occasions at intervals of 12 days - the treatment closest to the foraging pattern of wild birds. In July of the following summer shoot nitrogen content did not differ among the exclosed plots, irrespective of the treatment in 1987, and all values were lower than that for shoots from adjacent swards which were grazed and fertilized by wild geese. (6) The results show that NAPP and the nutritional quality of forage are dependent on faecal input, the number and timing of the grazing events and the phenology of plant growth. The role of the herbivore in maintaining grazing lawns of Puccinellia is discussed. DOI
