43. Gibeau, P; Palen, WJ. (2021) Impacts of run-of-river hydropower on coho salmon (Oncorhynchus kisutch): the role of density-dependent survival.Ecosphere 12 Impacts of run-of-river hydropower on coho salmon (Oncorhynchus kisutch): the role of density-dependent survival
anthropogenic impacts; flow fluctuations; matrix model; population dynamics; small dams
Predicting whether anthropogenic sources of mortality have negative consequences at the level of population dynamics is challenged by mechanisms like density-dependent survival that can amplify or offset the loss of individuals from anthropogenic disturbances. Run-of-river (RoR) hydropower is a growing industry that can cause frequent mortality of salmonid fry through rapid reductions in streamflow, leading to stranding on dewatered shores. However, whether individual-level impacts reduce population growth rates or increase local extinction risk is difficult to predict. We used a stochastic stage-structured matrix model to evaluate how the timing and magnitude of anthropogenic flow fluctuations impacted population abundance and extinction risk of coho salmon (Oncorhynchus kisutch), which spend up to 1.5 yr in many streams regulated by RoR hydropower. We additionally assessed how the timing (spring, winter) and strength (weak, moderate, high) of natural density-dependent bottlenecks experienced by salmon in freshwaters tempers or amplifies the potential for RoR-induced mortality to scale to emergent population dynamics. We compared population sizes and the 45-yr probability of quasi-extinction under 12 scenarios that varied the frequency (0-20 events per year) and magnitude (1-10% mortality per event) of RoR-induced flow fluctuations, as well as the timing and strength of density-dependent bottlenecks occurring during the first year in freshwater. We found that even mild flow fluctuations by RoR hydropower can impact coho salmon population dynamics, especially if density dependence is weak or occurs early in freshwater residency (spring). When density dependence was strong and during winter, the potential for population-level impact was lessened, but populations still declined by 13-42% when RoR-induced mortality was severe (5-10%) or frequent (10-20 events/yr). We conclude that strong density-dependent survival bottlenecks could partially mitigate the loss of fry from anthropogenic flow fluctuations, especially if bottlenecks occur late in freshwater residency, but not for all intensities of flow fluctuations. Even with strong density dependence in winter, our models predict declining populations by up to 70% under strong and very frequent flow fluctuations, which should serve to caution those tasked with regulating flows in streams affected by RoR hydropower. DOI
42. Greenberg, DA; Palen, WJ. (2021) Hydrothermal physiology and climate vulnerability in amphibians.Proc. R. Soc. B-Biol. Sci. 288 Hydrothermal physiology and climate vulnerability in amphibians
dehydration; desiccation; ecophysiology; frogs; global change; thermal performance
Concerns over the consequences of global climate change for biodiversity have spurred a renewed interest in organismal thermal physiology. However, temperature is only one of many environmental axes poised to change in the future. In particular, hydrologic regimes are also expected to shift concurrently with temperature in many regions, yet our understanding of how thermal and hydration physiology jointly affect performance and fitness is still limited for most taxonomic groups. Here, we investigated the relationship between functional performance, hydration state and temperature in three ecologically distinct amphibians, and compare how temperature and water loss can concurrently limit activity under current climate conditions. We found that performance was maintained across a broad range of hydration states in all three species, but then declines abruptly after a threshold of 20-30% mass loss. This rapid performance decline was accelerated when individuals were exposed to warmer temperatures. Combining our empirical hydrothermal performance curves with species-specific biophysical models, we estimated that dehydration can increase restrictions on species' activity by up to 60% compared to restriction by temperature alone. These results illustrate the importance of integrating species' hydration physiology into forecasts of climate vulnerability, as omitting this axis may significantly underestimate the effects of future climate change on Earth's biological diversity. DOI PubMed
41. Higgins, K; Guerrel, J; Lassiter, E; Mooers, A; Palen, WJ; Ibanez, R. (2021) Observations on spindly leg syndrome in a captive population of Andinobates geminisae.Zoo Biol. 40: 330-341 Observations on spindly leg syndrome in a captive population of Andinobates geminisae
amphibian calcium metabolism; amphibian captive husbandry; amphibian health; Andinobates geminisae; Anura; bone development; captive breeding; Dendrobatidae; metamorphosis; spindly leg syndrome (SLS); tadpole
Amphibian health problems of unknown cause limit the success of the growing number of captive breeding programs. Spindly leg syndrome (SLS) is one such disease, where affected individuals with underdeveloped limbs often require euthanization. We experimentally evaluated husbandry-related factors of SLS in a captive population of the critically endangered frog, Andinobates geminisae. SLS has been linked to tadpole nutrition, vitamin B deficiency, water filtration methods, and water quality, but few of these have been experimentally tested. We tested the effects of water filtration method and vitamin supplementation (2017) and the effects of tadpole husbandry protocol intensity (2018) on time to metamorphosis and the occurrence of SLS. We found that vitamin supplementation and reconstituted reverse osmosis filtration of tadpole rearing water significantly reduced SLS prevalence and that reduced tadpole husbandry delayed time to metamorphosis. A fortuitous accident in 2018 resulted in a decrease in the phosphate content of rearing water, which afforded us an additional opportunity to assess the influence of phosphate on calcium sequestration. We found that tadpoles that had more time to sequester calcium for ossification during development had decreased the prevalence of SLS. Taken together, our results suggest that the qualities of the water used to rear tadpoles plays an important role in the development of SLS. Specifically, filtration method, vitamin supplementation, and calcium availability of tadpole rearing water may play important roles. Focused experiments are still needed, but our findings provide important information for amphibian captive rearing programs affected by high SLS prevalence. DOI PubMed
40. Dare, GC; Murray, RG; Courcelles, DMM; Malt, JM; Palen, WJ. (2020) Run-of-river dams as a barrier to the movement of a stream-dwelling amphibian.Ecosphere 11 Run-of-river dams as a barrier to the movement of a stream-dwelling amphibian
Ascaphus truei; barrier; connectivity; dam; downstream drift; migration; run of river; small hydropower
Human activities frequently create structures that alter the connectivity among habitats or act as barriers to the natural movement of animals. Movement allows individuals to access different habitats, connect life history stages, and maintain genetic diversity. Here, we evaluated whether run-of-river (RoR) hydropower projects, an emerging renewable energy source in British Columbia, interrupt the longitudinal connectivity among larval stream amphibians, by altering larval rearing densities, with possible repercussions on growth and survival. In three watersheds, we tested for differences in the average upstream and downstream density of larval coastal tailed frog (Ascaphus truei), as well as changes to their longitudinal distribution upstream of the dams, as would be expected if RoR dams or their headponds act as barriers to the natural downstream drift of larvae. We found a 60% decrease in larval densities downstream compared to upstream of dams, consistent with RoR dams interrupting the natural pattern of downstreamA. trueidrift. Larval densities in the first 10 m above RoR headponds were 3 times higher compared to 100 m upstream, and when expressed in terms of relative abundance, we find a similar pattern, with between 2.5 and 3 times more larvae in the first 10 m above of the headpond than expected if larvae followed a uniform distribution. Our results are consistent with the hypothesis that RoR dams alter the spatial connectivity ofA. trueilarvae, leading to an accumulation of larvae directly above the dam, with unknown consequences for larval growth and survival. Our findings suggest caution is warranted when interpreting before-after monitoring studies that are often used to evaluate the impact of dams, whereby we find that reductions in downstream densities could be due to interruptions of downstream movement as opposed to direct mortality. DOI
39. Gibeau, P; Bradford, MJ; Palen, WJ. (2020) Can the creation of new freshwater habitat demographically offset losses of Pacific salmon from chronic anthropogenic mortality?PLoS One 15 Can the creation of new freshwater habitat demographically offset losses of Pacific salmon from chronic anthropogenic mortality?
Over 1 billion USD are devoted annually to rehabilitating freshwater habitats to improve survival for the recovery of endangered salmon populations. Mitigation often requires the creation of new habitat (e.g. habitat offsetting) to compensate population losses from human activities, however offsetting schemes are rarely evaluated. Anadromous Pacific salmon are ecologically, culturally, and economically important in the US and Canada, and face numerous threats from degradation of freshwater habitats. Here we used a matrix population model of coho salmon (Oncorhynchus kisutch) to determine the amount of habitat offsetting needed to compensate mortality (2-20% per year) caused by a range of development activities. We simulated chronic mortality to three different life stages (egg, parr, smolt/adult), individually and simultaneously, to mimic impacts from development, and evaluated if the number of smolts produced from constructed side-channels demographically offset losses. We show that under ideal conditions, the typical size of a constructed side-channel in the Pacific Northwest (PNW) (3405 m(2)) is sufficient to compensate for only relatively low levels of chronic mortality to either the parr or smolt/adult stages (2-7% per year), but populations do not recover if mortality is >10% per year. When we assumed lower productivity (e.g.; 25(th) percentile), we found that constructed channels would need to be 2.5-4.5 fold larger as compared to the typical size built in the PNW, respectively, to maintain population sizes. Moreover, when we imposed mortality to parr and smolt/adult stages simultaneously, we found that constructed side-channels would need to be between 1.8- and 2.3- fold larger that if the extra chronic mortality was imposed to one life stage only. We conclude that habitat offsetting has the potential to mitigate chronic mortality to early life stages, but that realistic assumptions about productivity of constructed side-channels and cumulative effects of anthropogenic disturbances on multiple life stages need to be considered. DOI PubMed
38. Gibeau, P; Palen, WJ. (2020) Predicted effects of flow diversion byRun-of-Riverhydropower on bypassed stream temperature and bioenergetics of salmonid fishes.River Res. Appl. 36: 1903-1915 Predicted effects of flow diversion byRun-of-Riverhydropower on bypassed stream temperature and bioenergetics of salmonid fishes
anthropogenic disturbance; flow regulation; individual growth; rainbow trout; renewable energy
Many anthropogenic disturbances impact stream ecosystems by changing flow and temperature regimes. The emerging industry of small Run-of-River (RoR) hydropower reduces streamflow in bypassed reaches, with largely unknown consequences for water temperatures and fish growth. We used empirical and simulated data from two small RoR regulated streams in British Columbia (Canada) to quantify changes in water temperatures in bypassed reaches and assess the potential impacts to resident rainbow trout (Oncorhynchus mykiss) growth using bioenergetics models under a range of consumption scenarios. We found increases in mean monthly water temperature in bypassed reaches due to flow diversion of 0.5-0.8 degrees C (0.17-0.19 degrees C/km). Bioenergetics models using those temperatures predicted increases in annualO. mykissgrowth (compared to natural temperatures) if consumption was unlimited (+200-450%), increases (+15-42%) if consumption was scaled with higher metabolic demand, and small reductions (-5 to 7%) if consumption remained constant. If food availability was reduced by 25%, annual growth was predicted to decline by 45%. Empirical estimates of annual growth of fish sampled indicate modest reductions in annual growth less severe than those modelled by our Scenario 2. Our results highlight that increases in water temperature induced by flow diversion for small RoR hydropower could be large enough to have consequences forO. mykissgrowth, but the impacts depend on how and when RoR hydropower affects food supply and consumption. DOI
37. Lertzman-Lepofsky, GF; Kissel, AM; Sinervo, B; Palen, WJ. (2020) Water loss and temperature interact to compound amphibian vulnerability to climate change.Glob. Change Biol. 26: 4868-4879 Water loss and temperature interact to compound amphibian vulnerability to climate change
climate change; desiccation; environmental risk; facultative behaviour; hydroregulation; physiology; thermoregulation
Ectotherm thermal physiology is frequently used to predict species responses to changing climates, but for amphibians, water loss may be of equal or greater importance. Using physical models, we estimated the frequency of exceeding the thermal optimum (T-opt) or critical evaporative water loss (EWLcrit) limits, with and without shade- or water-seeking behaviours. Under current climatic conditions (2002-2012), we predict that harmful thermal (>T-opt) and hydric (>EWLcrit) conditions limit the activity of amphibians during similar to 70% of snow-free days in sunny habitats. By the 2080s, we estimate that sunny and dry habitats will exceed one or both of these physiological limits during 95% of snow-free days. Counterintuitively, we find that while wet environments eliminate the risk of critical EWL, they do not reduce the risk of exceeding T-opt (+2% higher). Similarly, while shaded dry environments lower the risk of exceeding T-opt, critical EWL limits are still exceeded during 63% of snow-free days. Thus, no single environment that we evaluated can simultaneously reduce both physiological risks. When we forecast both temperature and EWL into the 2080s, both physiological thresholds are exceeded in all habitats during 48% of snow-free days, suggesting that there may be limited opportunity for behaviour to ameliorate climate change. We conclude that temperature and water loss act synergistically, compounding the ecophysiological risk posed by climate change, as the combined effects are more severe than those predicted individually. Our results suggest that predictions of physiological risk posed by climate change that do not account for water loss in amphibians may be severely underestimated and that there may be limited scope for facultative behaviours to mediate rapidly changing environments. DOI PubMed
36. Popescu, VD; Munshaw, RG; Shackelford, N; Pouzols, FM; Dubman, E; Gibeau, P; Horne, M; Moilanen, A; Palen, WJ. (2020) Quantifying biodiversity trade-offs in the face of widespread renewable and unconventional energy development.Sci Rep 10 Quantifying biodiversity trade-offs in the face of widespread renewable and unconventional energy development
The challenge of balancing biodiversity protection with economic growth is epitomized by the development of renewable and unconventional energy, whose adoption is aimed at stemming the impacts of global climate change, yet has outpaced our understanding of biodiversity impacts. We evaluated the potential conflict between biodiversity protection and future electricity generation from renewable (wind farms, run-of-river hydro) and non-renewable (shale gas) sources in British Columbia (BC), Canada using three metrics: greenhouse gas (GHG) emissions, electricity cost, and overlap between future development and conservation priorities for several fish and wildlife groups - small-bodied vertebrates, large mammals, freshwater fish - and undisturbed landscapes. Sharp trade-offs in global versus regional biodiversity conservation exist for all energy technologies, and in BC they are currently smallest for wind energy: low GHG emissions, low-moderate overlap with top conservation priorities, and competitive energy cost. GHG emissions from shale gas are 1000 times higher than those from renewable sources, and run-of-river hydro has high overlap with conservation priorities for small-bodied vertebrates. When all species groups were considered simultaneously, run-of-river hydro had moderate overlap (0.56), while shale gas and onshore wind had low overlap with top conservation priorities (0.23 and 0.24, respectively). The unintended cost of distributed energy sources for regional biodiversity suggest that trade-offs based on more diverse metrics must be incorporated into energy planning. DOI PubMed
35. Coristine, LE; Colla, S; Bennett, N; Carlsson, AM; Davy, C; Davies, KTA; Favaro, B; Flockhart, DTT; Fraser, K; Orihel, D; Otto, SP; Palen, W; Polfus, JL; Venter, O; Ford, AT. (2019) National contributions to global ecosystem values.Conserv. Biol. 33: 1219-1223 National contributions to global ecosystem values
breeding habitat; freshwater; global resource supply; marine productivity; policy; range shift; soil carbon storage; wilderness
Current conservation templates prioritize biogeographic regions with high intensity ecosystem values, such as exceptional species richness or threat. Intensity-based targets are an important consideration in global efforts, but they do not capture all available opportunities to conserve ecosystem values, including those that accrue in low intensity over large areas. We assess six globally-significant ecosystem values-intact wilderness, freshwater availability, productive marine environments, breeding habitat for migratory wildlife, soil carbon storage, and latitudinal potential for range shift in the face of climate change-to highlight opportunities for high-impact broadly-distributed contributions to global conservation. Nations can serve as a cohesive block of policy that can profoundly influence conservation outcomes. Contributions to global ecosystem values that exceed what is predicted by a nation's area alone, can give rise to countries with the capacity to act as 'conservation superpowers', such as Canada and Russia. For these conservation superpowers, a relatively small number of national policies can have environmental repercussions for the rest of the world. DOI PubMed
34. Gooswin, KJA; Kissel, AM; Palen, WJ. (2019) INDIVIDUAL VARIATION IN THERMAL PERFORMANCE OF A TEMPERATE, MONTANE AMPHIBIAN (RANA CASCADAE).Herpetol. Conserv. Biol. 14: 420-428 INDIVIDUAL VARIATION IN THERMAL PERFORMANCE OF A TEMPERATE, MONTANE AMPHIBIAN (RANA CASCADAE)
Cascades Frog; in situ; mass; Mount Rainier National Park; thermal optima; thermal physiology
Temperate, montane amphibians are experiencing rapid environmental change. Better mechanistic understanding of the response of montane amphibians to accelerating changes in air and water temperatures can provide a basis for robust predictions of the vulnerability of species to future climate change. Thermal performance curves allow for quantitative predictions of responses to temperatures beyond which locomotor physiology is compromised. We designed a field-based thermal performance assay to evaluate the frequency that adult Cascades Frogs (Rana cascadae) are exposed to harmful environmental temperatures. We fit a suite of generalized additive models in an information theoretic framework to estimate thermal performance curves and found Rana cascadae optimal performance temperatures (T-opt) vary as a function of mass. The T-opt for the median mass of individuals in our study (17.9 g) was 20.7 degrees C and critical thermal maximum (CTmax) was 34.0 degrees C. We calculated the number of days during the growing season (1 July to 30 September) that the temperature exceeded the upper bound of the 80% maximal performance breadth (T-br80), a conservative performance metric beyond which activity drops substantially, and CTmax for the median, 25th, and 75th percentile masses in our study using contemporary weather data from 1990 to 2015. Rana cascadae did not experience temperatures exceeding CTmax, but Tbr80 was exceeded 3-13 d per summer, depending on frog size. Our results emphasize that larger individuals may be more susceptible to extreme warm temperatures. Thermal performance studies not accounting for individual variation should be interpreted cautiously.
32. Kissel, AM; Palen, WJ; Ryan, ME; Adams, MJ. (2019) Compounding effects of climate change reduce population viability of a montane amphibian.Ecol. Appl. 29 Compounding effects of climate change reduce population viability of a montane amphibian
amphibians; climate change; extinction risk; hydrology; montane ecosystems; population modeling
Anthropogenic climate change presents challenges and opportunities to the growth, reproduction, and survival of individuals throughout their life cycles. Demographic compensation among life-history stages has the potential to buffer populations from decline, but alternatively, compounding negative effects can lead to accelerated population decline and extinction. In montane ecosystems of the U.S. Pacific Northwest, increasing temperatures are resulting in a transition from snow-dominated to rain-dominated precipitation events, reducing snowpack. For ectotherms such as amphibians, warmer winters can reduce the frequency of critical minimum temperatures and increase the length of summer growing seasons, benefiting post-metamorphic stages, but may also increase metabolic costs during winter months, which could decrease survival. Lower snowpack levels also result in wetlands that dry sooner or more frequently in the summer, increasing larval desiccation risk. To evaluate how these challenges and opportunities compound within a species' life history, we collected demographic data on Cascades frog (Rana cascadae) in Olympic National Park in Washington state to parameterize stage-based stochastic matrix population models under current and future (A1B, 2040s, and 2080s) environmental conditions. We estimated the proportion of reproductive effort lost each year due to drying using watershed-specific hydrologic models, and coupled this with an analysis that relates 15 yr of R. cascadae abundance data with a suite of climate variables. We estimated the current population growth (lambda(s)) to be 0.97 (95% CI 0.84-1.13), but predict that lambda(s) will decline under continued climate warming, resulting in a 62% chance of extinction by the 2080s because of compounding negative effects on early and late life history stages. By the 2080s, our models predict that larval mortality will increase by 17% as a result of increased pond drying, and adult survival will decrease by 7% as winter length and summer precipitation continue to decrease. We find that reduced larval survival drives initial declines in the 2040s, but further declines in the 2080s are compounded by decreases in adult survival. Our results demonstrate the need to understand the potential for compounding or compensatory effects within different life history stages to exacerbate or buffer the effects of climate change on population growth rates through time. DOI PubMed
31. Greenberg, DA; Palen, WJ; Chan, KC; Jetz, W; Mooers, AO. (2018) Evolutionarily distinct amphibians are disproportionately lost from human-modified ecosystems.Ecology Letters 21 Evolutionarily distinct amphibians are disproportionately lost from human-modified ecosystems
diversification; extinction risk; forests; global change; grasslands; habitat loss; land conversion; phylogenetic diversity
Humans continue to alter terrestrial ecosystems, but our understanding of how biodiversity responds is still limited. Anthropogenic habitat conversion has been associated with the loss of evolutionarily distinct bird species at local scales, but whether this evolutionary pattern holds across other clades is unknown. We collate a global dataset on amphibian assemblages in intact forests and nearby human-modified sites to assess whether evolutionary history influences susceptibility to land conversion. We found that evolutionarily distinct amphibian species are disproportionately lost when forested habitats are converted to alternative land-uses. We tested the hypothesis that grassland-associated amphibian lineages have both higher diversification and are pre-adapted to human landscapes, but found only weak evidence supporting this. The loss of evolutionarily distinct amphibians with land conversion suggests that preserving remnant forests will be vital if we aim to preserve the amphibian tree of life in the face of mounting anthropogenic pressures. DOI PubMed
29. Gibeau, P; Connors, BM; Palen, WJ. (2017) Run-of-River hydropower and salmonids: potential effects and perspective on future research.Canadian Journal of Fisheries and Aquatic Sciences 74: 1135-1149 Run-of-River hydropower and salmonids: potential effects and perspective on future research
The spatial footprint of individual run-of-river (RoR) hydropower facilities is smaller than reservoir-storage hydroelectric projects and their impacts to aquatic ecosystems are often assumed to be negligible. However, these effects are poorly understood, especially for salmonids whose freshwater habitat often overlaps with RoR hydropower potential. Flow regulation for RoR hydropower is unique in how it influences the seasonality and magnitude of flow diversion and because low-head dams can be overtopped at high flows. Based on a review of the primary literature, we identified three pathways of effects by which RoR hydropower may influence salmonids: reduction of flow, presence of low-head dams impounding rivers, and anthropogenic flow fluctuations. We synthesized empirical evidence of effects of RoR hydropower on river ecosystems from 31 papers, of which only 10 explicitly considered salmonids. We identified key research gaps including impacts of extended low-flow periods, anthropogenic flow fluctuations, and cumulative effects of multiple RoR projects. Filling these gaps is necessary to help manage and conserve salmonid populations in the face of the growing global demand for small-scale hydropower. DOI
28. Green, SJ; Demes, K; Arbeider, M; Palen, WJ; Salomon, AK; Sisk, TD; Webster, M; Ryan, ME. (2017) Oil sands and the marine environment: current knowledge and future challenges.Frontiers in Ecology and the Environment 15: 74-83 Oil sands and the marine environment: current knowledge and future challenges
The environmental consequences of bitumen extraction from oil sands deposits are at the center of North American natural resource and energy policy debate, yet impacts on ocean environments have received little attention. Using a quantitative framework, we identify knowledge gaps and research needs related to the effects of oil sands development on marine biota. Fifteen sources of stress and disturbance - varying greatly in spatial and temporal scale - are generated via two pathways: (1) the coastal storage and oceanic transport of bitumen products, and (2) the contribution of industry-derived greenhouse gases to climate change in the ocean. Of highest research priority are the fate, behavior, and biological effects of bitumen in the ocean. By contrast, climate-change impacts are scientifically well established but not considered in key regulatory processes. Most stressors co-occur and are generated by other industries, yet cumulative effects are so far unaccounted for in decision making associated with new projects. Our synthesis highlights priority research needed to inform future energy development decisions, and opportunities for policy processes to acknowledge the full scope of potential and realized environmental consequences. DOI
27. Greenberg, DA; Palen, WJ; Mooers, AO. (2017) Amphibian species traits, evolutionary history and environment predict Batrachochytrium dendrobatidis infection patterns, but not extinction risk.Evol. Appl. 10: 1130-1145 Amphibian species traits, evolutionary history and environment predict Batrachochytrium dendrobatidis infection patterns, but not extinction risk
amphibian; Batrachochytrium dendrobatidis; chytridiomycosis; extinction; phylogeny; resistance; tolerance; traits
The fungal pathogen Batrachochytrium dendrobatidis (B.dendrobatidis) has emerged as a major agent of amphibian extinction, requiring conservation intervention for many susceptible species. Identifying susceptible species is challenging, but many aspects of species biology are predicted to influence the evolution of host resistance, tolerance, or avoidance strategies towards disease. In turn, we may expect species exhibiting these distinct strategies to differ in their ability to survive epizootic disease outbreaks. Here, we test for phylogenetic and trait-based patterns of B.dendrobatidis infection risk and infection intensity among 302 amphibian species by compiling a global data set of B.dendrobatidis infection surveys across 95 sites. We then use best-fit models that associate traits, taxonomy and environment with B.dendrobatidis infection risk and intensity to predict host disease mitigation strategies (tolerance, resistance, avoidance) for 122 Neotropical amphibian species that experienced epizootic B.dendrobatidis outbreaks, and noted species persistence or extinction from these events. Aspects of amphibian species life history, habitat use and climatic niche were consistently linked to variation in B.dendrobatidis infection patterns across sites around the world. However, predicted B.dendrobatidis infection risk and intensity based on site environment and species traits did not reveal a consistent pattern between the predicted host disease mitigation strategy and extinction outcome. This suggests that either tolerant or resistant species may have no advantage in ameliorating disease during epizootic events, or that other factors drive the persistence of amphibian populations during chytridiomycosis outbreaks. These results suggest that using a trait-based approach may allow us to identify species with resistance or tolerance to endemic B.dendrobatidis infections, but that this approach may be insufficient to ultimately identify species at risk of extinction from epizootics. DOI
26. Kissel, AM; Palen, WJ; Govindarajulu, P. (2017) A Decision-theory Approach to Cost-effective Population Supplementation for Imperiled Species.Ecol. Econ. 142: 194-202 A Decision-theory Approach to Cost-effective Population Supplementation for Imperiled Species
Species recovery; Decision analysis; Population supplementation; Recovery costs; Amphibian decline
Despite decades of managing endangered species, few have been successfully recovered. One option to reduce this gap is to use decision analysis to weigh alternative recovery actions. Using decision analysis, we evaluated tradeoffs between recovery actions to reduce extinction risk and financial cost for the imperiled Oregon spotted frog (Rana pretiosa). We simulated population supplementation via captive breeding or head-starting, and releasing offspring into the wild as larvae or young of the year. We ranked the efficacy of recovery scenarios, represented by a culmination of a series of decision points, to reduce the 10-year extinction risk below 10% while minimizing financial costs. We explored how rankings varied with respect to the extinction risk target, the endangered population size, and the reproductive output captive females. Our top-ranked pathway was to supplement with captive bred larvae, resulting in a 3% reduction in extinction risk for every $100,000 spent. In general, supplementing with captive bred larvae resulted in the biggest reduction in extinction risk per dollar invested. Additionally, we found that increasing spending does not always result in a proportional reduction in extinction risk. These results link quantitative and applied conservation by considering the biological and economic efficacy. to recover endangered species. (C) 2017 Elsevier B.V. All rights reserved. DOI
25. Muths, E; Chambert, T; Schmidt, BR; Miller, DAW; Hossack, BR; Joly, P; Grolet, O; Green, DM; Pilliod, DS; Cheylan, M; Fisher, RN; McCaffery, RM; Adams, MJ; Palen, WJ; Arntzen, JW; Garwood, J; Fellers, G; Thirion, JM; Besnard, A; Grant, EHC. (2017) Heterogeneous responses of temperate-zone amphibian populations to climate change complicates conservation planning.Sci Rep 7 Heterogeneous responses of temperate-zone amphibian populations to climate change complicates conservation planning
The pervasive and unabated nature of global amphibian declines suggests common demographic responses to a given driver, and quantification of major drivers and responses could inform broad-scale conservation actions. We explored the influence of climate on demographic parameters (i.e., changes in the probabilities of survival and recruitment) using 31 datasets from temperate zone amphibian populations (North America and Europe) with more than a decade of observations each. There was evidence for an influence of climate on population demographic rates, but the direction and magnitude of responses to climate drivers was highly variable among taxa and among populations within taxa. These results reveal that climate drivers interact with variation in life-history traits and population-specific attributes resulting in a diversity of responses. This heterogeneity complicates the identification of conservation 'rules of thumb' for these taxa, and supports the notion of local focus as the most effective approach to overcome global-scale conservation challenges. DOI
24. Fuller, TK; Venditti, JG; Nelson, PA; Palen, WJ. (2016) Modeling grain size adjustments in the downstream reach following run-of-river development.Water Resources Research 52: 2770-2788 Modeling grain size adjustments in the downstream reach following run-of-river development
Disruptions to sediment supply continuity caused by run-of-river (RoR) hydropower development have the potential to cause downstream changes in surface sediment grain size which can influence the productivity of salmon habitat. The most common approach to understanding the impacts of RoR hydropower is to study channel changes in the years following project development, but by then, any impacts are manifest and difficult to reverse. Here we use a more proactive approach, focused on predicting impacts in the project planning stage. We use a one-dimensional morphodynamic model to test the hypothesis that the greatest risk of geomorphic change and impact to salmon habitat from a temporary sediment supply disruption exists where predevelopment sediment supply is high and project design creates substantial sediment storage volume. We focus on the potential impacts in the reach downstream of a powerhouse for a range of development scenarios that are typical of projects developed in the Pacific Northwest and British Columbia. Results indicate that increases in the median bed surface size (D-50) are minor if development occurs on low sediment supply streams (<1 mm for supply rates 1 x 10(-5) m(2) s(-1) or lower), and substantial for development on high sediment supply streams (8-30 mm for supply rates between 5.5 x 10(-4) and 1 x 10(-3) m(2) s(-1)). However, high sediment supply streams recover rapidly to the predevelopment surface D-50 (similar to 1 year) if sediment supply can be reestablished. DOI
23. Lee, SY; Ryan, ME; Hamlet, AF; Palen, WJ; Lawler, JJ; Halabisky, M. (2015) Projecting the Hydrologic Impacts of Climate Change on Montane Wetlands.PLoS One 10 Projecting the Hydrologic Impacts of Climate Change on Montane Wetlands
Wetlands are globally important ecosystems that provide critical services for natural communities and human society. Montane wetland ecosystems are expected to be among the most sensitive to changing climate, as their persistence depends on factors directly influenced by climate (e.g. precipitation, snowpack, evaporation). Despite their importance and climate sensitivity, wetlands tend to be understudied due to a lack of tools and data relative to what is available for other ecosystem types. Here, we develop and demonstrate a new method for projecting climate-induced hydrologic changes in montane wetlands. Using observed wetland water levels and soil moisture simulated by the physically based Variable Infiltration Capacity (VIC) hydrologic model, we developed site-specific regression models relating soil moisture to observed wetland water levels to simulate the hydrologic behavior of four types of montane wetlands (ephemeral, intermediate, perennial, permanent wetlands) in the U.S. Pacific Northwest. The hybrid models captured observed wetland dynamics in many cases, though were less robust in others. We then used these models to a) hindcast historical wetland behavior in response to observed climate variability (1916-2010 or later) and classify wetland types, and b) project the impacts of climate change on montane wetlands using global climate model scenarios for the 2040s and 2080s (A1B emissions scenario). These future projections show that climate-induced changes to key driving variables (reduced snowpack, higher evapotranspiration, extended summer drought) will result in earlier and faster drawdown in Pacific Northwest montane wetlands, leading to systematic reductions in water levels, shortened wetland hydroperiods, and increased probability of drying. Intermediate hydroperiod wetlands are projected to experience the greatest changes. For the 2080s scenario, widespread conversion of intermediate wetlands to fastdrying ephemeral wetlands will likely reduce wetland habitat availability for many species. DOI
22. Murray, RG; Popescu, VD; Palen, WJ; Govindarajulu, P. (2015) Relative performance of ecological niche and occupancy models for predicting invasions by patchily-distributed species.Biological Invasions 17: 2691-2706 Relative performance of ecological niche and occupancy models for predicting invasions by patchily-distributed species
British Columbia; Freshwater habitat gradient; Anuran; Invasive species; Lithobates catesbeianus; Lithobates clamitans; Occupancy models; Species distribution models; Wetlands
Ecological niche models (ENM) have been used with mixed success for predicting the geographic extent of non-native species to aid management and conservation. This approach is problematic for predicting invasions of patchily-distributed species (e.g., pond-breeding amphibians), whose occurrence is often determined by local habitat conditions. Here, we tested the performance of bioclimatic ENM for predicting occurrence (from repeated surveys) of two non-native pond-breeding anurans at 71 wetlands in British Columbia, Canada: permanent pond specialist American bullfrog (Lithobates catesbeianus), and generalist green frog (Lithobates clamitans). For L. catesbeianus, we assessed the risk of invasion beyond the invasion front. We found higher correlation between ENM and occupancy predictions for L. clamitans (r(s) = 0.58), than for L. catesbeianus (r(s) = -0.26). L. clamitans occurrence was highest at low elevations and high annual precipitation; in contrast, L. catesbeianus occupancy was predicted by wetland connectivity and distance from a historic introduction site [low at isolated ponds >50 km from the introduction site, and high (>0.8) at all ponds with >10 % water within 500 m]. Conditional on successful dispersal, four sites beyond the L. catesbeianus invasion front surveyed in this study were at high risk of invasion due to high habitat suitability (proportion of area occupied = 0.33; 0.04-0.83, 95 % CI). In conclusion, ENMs may be useful for informing invasion management for climate driven wetland species, but repeated sampling is necessary to predict invasions for habitat-driven wetland species. DOI
21. Atlas, WI; Palen, WJ. (2014) Prey Vulnerability Limits Top-Down Control and Alters Reciprocal Feedbacks in a Subsidized Model Food Web.PLOS One 9 Prey Vulnerability Limits Top-Down Control and Alters Reciprocal Feedbacks in a Subsidized Model Food Web
Resource subsidies increase the productivity of recipient food webs and can affect ecosystem dynamics. Subsidies of prey often support elevated predator biomass which may intensify top-down control and reduce the flow of reciprocal subsidies into adjacent ecosystems. However, top-down control in subsidized food webs may be limited if primary consumers posses morphological or behavioral traits that limit vulnerability to predation. In forested streams, terrestrial prey support high predator biomass creating the potential for strong top-down control, however armored primary consumers often dominate the invertebrate assemblage. Using empirically based simulation models, we tested the response of stream food webs to variations in subsidy magnitude, prey vulnerability, and the presence of two top predators. While terrestrial prey inputs increased predator biomass (+12%), the presence of armored primary consumers inhibited top-down control, and diverted most aquatic energy (similar to 75%) into the riparian forest through aquatic insect emergence. Food webs without armored invertebrates experienced strong trophic cascades, resulting in higher algal (similar to 50%) and detrital (similar to 1600%) biomass, and reduced insect emergence (-90%). These results suggest prey vulnerability can mediate food web responses to subsidies, and that top-down control can be arrested even when predator-invulnerable consumers are uncommon (20%) regardless of the level of subsidy. DOI
20. Gerick, AA; Munshaw, RG; Palen, WJ; Combes, SA; O'Regan, SM. (2014) Thermal physiology and species distribution models reveal climate vulnerability of temperate amphibians.Journal of Biogeography 41: 713-723 Thermal physiology and species distribution models reveal climate vulnerability of temperate amphibians
Ecological niche models; global climate change; Pseudacris regilla; Rana aurora; Spea intermontana; thermal physiology
AimHigh-latitude ectotherms are predicted to be less physiologically vulnerable to climate warming than tropical species based on their larger thermal safety margins, the distance between ambient temperatures and species' thermal optima. We sought to test the prediction that high latitude amphibians are buffered against the impacts of climate warming. LocationBritish Columbia, Canada. MethodsWe estimated the risk from climate change for three high-latitude amphibian species (Spea intermontana, Rana aurora and Pseudacris regilla) by combining thermal performance experiments with species distribution models and predicted changes in maximum summer temperatures through the 2080s, in order to demonstrate temporal and geographical trends in vulnerability to climate warming among and within species. ResultsWe found that species have thermal safety margins of 3.2-3.8 degrees C based on current maximum summer temperatures. However, by the 2080s (emissions scenario A1B), we estimate that 45-82% of our focal species' current distributions will experience maximum summer temperatures above their thermal optima. We also found that by using long-term average temperatures, as some studies have done, there were almost no scenarios in which populations of any species were experiencing temperatures greater than their thermal optima. Main conclusionsCombining spatially explicit species distribution models with performance physiology allows us to predict where limiting temperatures will occur in the coming decades, and can guide climate mitigation and conservation efforts before populations decline. Despite moderate thermal safety margins, high-latitude ectotherms can be highly vulnerable to climate warming when spatio-temporal variation is incorporated into estimates of risk as a result of climate change. DOI
19. Kissel, AM; Palen, WJ; Govindarajulu, P; Bishop, CA. (2014) Quantifying Ecological Life Support: The Biological Efficacy of Alternative Supplementation Strategies for Imperiled Amphibian Populations.Conservation Letters 7: 441-450 Quantifying Ecological Life Support: The Biological Efficacy of Alternative Supplementation Strategies for Imperiled Amphibian Populations
Population supplementation; matrix models; captive breeding; head-start; amphibian conservation; species recovery
Global biodiversity loss has prompted diverse efforts to stem or reverse declines for many species. Such efforts are often implemented before the efficacy of alternative management actions is quantified. Here, we use matrix models to compare the effectiveness of two supplementation strategies, head-starting early life stages and captive breeding for reintroduction, at reducing extinction risk of declining amphibians. We use the imperiled Oregon spotted frog (Rana pretiosa) as a case study and find that when supplementation occurs after metamorphosis, captive breeding is more effective at reducing extinction risk than head-starting, but the difference declines with increasing supplementation effort. We also find that captive breeding with release as larvae yields similar reductions in extinction risk, and is two orders of magnitude more effective at reducing extinction probabilities than head-starting the same stage. Our results highlight that even basic demographic data can be leveraged to assess tradeoffs among alternative supplementation strategies. DOI
18. Munshaw, RG; Atlas, WI; Palen, WJ; Courcelles, DM; Monteith, ZL. (2014) Correlates and consequences of injury in a large, predatory stream salamander (Dicamptodon tenebrosus).Amphibia-Reptilia 35: 107-116 Correlates and consequences of injury in a large, predatory stream salamander (Dicamptodon tenebrosus)
Dicamptodon tenebrosus; aggression; resource competition; territorialism; population structure
Conspecific aggression is an important factor structuring population dynamics through intra-and interspecific interactions, but is rarely studied in un-manipulated populations. In this study, we evaluated rates of injury as a proxy for conspecific aggression using a depletion survey of predatory coastal giant salamanders (Dicamptodon tenebrosus) in a tributary of the South Fork Eel River, California. We tested a range of hypotheses including a suite of environmental and biotic factors for the rate of injury in a population by using an AIC model-selection approach that examined the weight of evidence for individual models. We examined both the probability of a given individual being injured, and the proportion of individuals within a given study pool being injured. We found strong support for models including salamander size, density of young-of-the-year steelhead, and density of the largest size-class of salamander as factors positively influencing the rate of injury at both the individual and habitat levels. We also found that density of older steelhead (1+ steelhead) had a strong, but highly variable positive impact on frequency of injury. This study shows that both conspecific and heterospecific factors influence intraspecific aggression for the dominant salamander throughout coastal Pacific Northwest streams. Our methodology demonstrates a non-manipulative approach to identifying correlates of natural injury in a cryptic species of amphibian. More work is needed to determine how these factors directly and indirectly influence the spatial distribution, individual fitness, and dynamics of salamander populations within streams. DOI
17. O'Regan, SM; Palen, WJ; Anderson, SC. (2014) Climate warming mediates negative impacts of rapid pond drying for three amphibian species.Ecology 95: 845-855 Climate warming mediates negative impacts of rapid pond drying for three amphibian species
Spea intermontana; global warming; wetland drying; metamorphosis; phenotypic plasticity; Rana aurora; Pseudacris regilla; life history
Anthropogenic climate change will present both opportunities and challenges for pool-breeding amphibians. Increased water temperature and accelerated drying may directly affect larval growth, development, and survival, yet the combined effects of these processes on larvae with future climate change remain poorly understood. Increased surface temperatures are projected to warm water and decrease water inputs, leading to earlier and faster wetland drying. So it is often assumed that larvae will experience negative synergistic impacts with combined warming and drying. However, an alternative hypothesis is that warming-induced increases in metabolic rate and aquatic resource availability might compensate for faster drying rates, generating antagonistic larval responses. We conducted a mesocosm experiment to test the individual and interactive effects of pool permanency (permanent vs. temporary) and water temperature (ambient vs. +similar to 3 degrees C) on three anurans with fast-to-slow larval development rates (Great Basin spadefoot [Spea intermontana], Pacific chorus frog [Pseudacris regilla], and northern red-legged frog [Rana aurora]). We found that although tadpoles in warmed pools reached metamorphosis 15-17 days earlier, they did so with little cost (<2 mm) to size, likely due to greater periphyton growth in warmed pools easing drying-induced resource competition. Warming and drying combined to act antagonistically on early growth (P = 0.06) and survival (P = 0.06), meaning the combined impact was less than the sum of the individual impacts. Warming and drying acted additively on time to and size at metamorphosis. These nonsynergistic impacts may result from cotolerance of larvae to warming and drying, as well as warming helping to offset negative impacts of drying. Our results indicate that combined pool warming and drying may not always be harmful for larval amphibians. However, they also demonstrate that antagonistic responses are difficult to predict, which poses a challenge to proactive conservation and management. Our study highlights the importance of considering the nature of multiple stressor interactions as amphibians are exposed to an increasing number of anthropogenic threats. DOI
16.Palen, WJ; Sisk, TD; Ryan, ME; Arvai, JL; Jaccard, M; Salomon, AK; Homer-Dixon, T; Lertzman, KP. (2014) Consider the global impacts of oil pipelines.Nature 510: 465-467 Consider the global impacts of oil pipelines
PubMed
15. Ryan, ME; Palen, WJ; Adams, MJ; Rochefort, RM. (2014) Amphibians in the climate vice: loss and restoration of resilience of montane wetland ecosystems in the western US.Frontiers in Ecology and the Environment 12: 232-240 Amphibians in the climate vice: loss and restoration of resilience of montane wetland ecosystems in the western US
Wetlands in the remote mountains of the western US have undergone two massive ecological experiments spanning the 20th century. Beginning in the late 1800s and expanding after World War II, fish and wildlife managers intentionally introduced millions of predatory trout (primarily Oncorhynchus spp) into fishless mountain ponds and lakes across the western states. These new top predators, which now occupy 95% of large mountain lakes, have limited the habitat distributions of native frogs, salamanders, and wetland invertebrates to smaller, more ephemeral ponds where trout do not survive. Now a second experiment - anthropogenic climate change - threatens to eliminate many of these ephemeral habitats and shorten wetland hydroperiods. Caught between climate-induced habitat loss and predation from introduced fish, native mountain lake fauna of the western US - especially amphibians - are at risk of extirpation. Targeted fish removals, guided by models of how wetlands will change under future climate scenarios, provide innovative strategies for restoring resilience of wetland ecosystems to climate change. DOI
14. Sunday, JM; Popovic, I; Palen, WJ; Foreman, MGG; Hart, MW. (2014) Ocean circulation model predicts high genetic structure observed in a long-lived pelagic developer.Molecular Ecology 23: 5036-5047 Ocean circulation model predicts high genetic structure observed in a long-lived pelagic developer
larval dispersal; marine connectivity; oceanographic circulation model; population genetics
Understanding the movement of genes and individuals across marine seascapes is a long-standing challenge in marine ecology and can inform our understanding of local adaptation, the persistence and movement of populations, and the spatial scale of effective management. Patterns of gene flow in the ocean are often inferred based on population genetic analyses coupled with knowledge of species' dispersive life histories. However, genetic structure is the result of time-integrated processes and may not capture present-day connectivity between populations. Here, we use a high-resolution oceanographic circulation model to predict larval dispersal along the complex coastline of western Canada that includes the transition between two well-studied zoogeographic provinces. We simulate dispersal in a benthic sea star with a 6-10week pelagic larval phase and test predictions of this model against previously observed genetic structure including a strong phylogeographic break within the zoogeographical transition zone. We also test predictions with new genetic sampling in a site within the phylogeographic break. We find that the coupled genetic and circulation model predicts the high degree of genetic structure observed in this species, despite its long pelagic duration. High genetic structure on this complex coastline can thus be explained through ocean circulation patterns, which tend to retain passive larvae within 20-50km of their parents, suggesting a necessity for close-knit design of Marine Protected Area networks. DOI PubMed
13. Tsui, MTK; Blum, JD; Finlay, JC; Balogh, SJ; Nollet, YH; Palen, WJ; Power, ME. (2014) Variation in Terrestrial and Aquatic Sources of Methylmercury in Stream Predators as Revealed by Stable Mercury Isotopes.Environmental Science & Technology 48: 10128-10135 Variation in Terrestrial and Aquatic Sources of Methylmercury in Stream Predators as Revealed by Stable Mercury Isotopes
Mercury (Hg) is widely distributed in the environment, and its organic form, methylmercury (MeHg), can extensively bioaccumulate and biomagnify in aquatic and terrestrial food webs. Concentrations of MeHg in organisms are highly variable, and the sources in natural food webs are often not well understood. This study examined stable isotope ratios of MeHg (mass-dependent fractionation, as delta Hg-202(MeHg); and mass-independent fractionation, as Delta Hg-199(MeHg)) in benthic invertebrates, juvenile steelhead trout (Oncorhynchus mykiss), and water striders (Gerris remigis) along a stream productivity gradient, as well as carnivorous terrestrial invertebrates, in a forested watershed at the headwater of South Fork Eel River in northern California. Throughout the sampling sites, delta Hg-202(MeHg) (after correction due to the effect of MeHg photodegradation) was significantly different between benthic (median = -1.40 parts per thousand; range, -2.34 to -0.78 parts per thousand; total number of samples = 29) and terrestrial invertebrates (median = +0.51 parts per thousand; range, -0.37 to +1.40 parts per thousand; total number of samples = 9), but no major difference between these two groups was found for Delta Hg-199(MeHg). Steelhead trout (52 individual fishes) have MeHg of predominantly aquatic origins, with a few exceptions at the upstream locations (e.g., 1 fish collected in a tributary had a purely terrestrial MeHg source and 4 fishes had mixed aquatic and terrestrial MeHg sources). Water striders (seven pooled samples) derive MeHg largely from terrestrial sources throughout headwater sections. These data suggest that direct terrestrial subsidy (e.g., terrestrial invertebrates falling into water) can be important for some stream predators in headwater streams and could represent an important means of transfer of terrestrially derived MeHg (e.g., in situ methylation within forests, atmospheric sources) to aquatic ecosystems. Moreover, these findings show that terrestrial subsidies can enhance MeHg bioaccumulation of consumers in headwater streams where aqueous MeHg levels are very low. DOI PubMed
12. Atlas, WI; Palen, WJ; Courcelles, DM; Munshaw, RG; Monteith, ZL. (2013) Dependence of stream predators on terrestrial prey fluxes: food web responses to subsidized predation.Ecosphere 4 Dependence of stream predators on terrestrial prey fluxes: food web responses to subsidized predation
Dicamptodon tenebrosus; Eel River; California; USA; experimental ecology; food webs; Oncorhynchus mykiss; resource subsidies; stream ecosystems; terrestrial-aquatic linkages; trophic cascades.
Resource subsidies in the form of energy, materials, and organisms can support the productivity of recipient ecosystems. When subsidies increase the abundance of top predators, theory predicts that top-down interactions will be strengthened. However, the degree to which subsidies intensify predation should be constrained by the strength of interactions between predators and their prey. To test the potential for subsidies to drive strong top-down control by two stream predators, steelhead (Oncorhynchus mykiss) and Pacific giant salamander (Dicamptodon tenebrosus) we reduced terrestrial prey and manipulated the presence of predators in 32 stream reaches. Prey subsidies supported elevated growth of predatory steelhead in our study system and in the absence of allochthonous prey steelhead experienced a 187% reduction in growth. Despite the high biomass of subsidized predators, there was little support for strong top-down control of herbivore biomass, or a trophic cascade as measured by changes in AFDM and chlorophyll-a. This result was consistent across subsidy treatments, suggesting that predatory steelhead are unable to increase exploitation of aquatic prey in the absence of terrestrial prey subsidies. The potential for top-down control was apparently limited by the fact that most (82%) herbivores in our study system were armored and relatively invulnerable to predation. These results demonstrate the potential importance of behavioral and morphological adaptations that can temper predator prey interactions in highly subsidized ecosystems. DOI
11. Munshaw, RG; Palen, WJ; Courcelles, DM; Finlay, JC. (2013) Predator-Driven Nutrient Recycling in California Stream Ecosystems.PLOS One 8 Predator-Driven Nutrient Recycling in California Stream Ecosystems
CRITICAL THERMAL MAXIMA; FOOD-WEB STRUCTURE; FRESH-WATER; PHOSPHORUS-LIMITATION; SALAMANDER DENSITY; MOUNTAIN LAKES; WESTERN OREGON; RAINBOW-TROUT; UNITED-STATES; GIZZARD SHAD
Nutrient recycling by consumers in streams can influence ecosystem nutrient availability and the assemblage and growth of photoautotrophs. Stream fishes can play a large role in nutrient recycling, but contributions by other vertebrates to overall recycling rates remain poorly studied. In tributaries of the Pacific Northwest, coastal giant salamanders (Dicamptodon tenebrosus) occur at high densities alongside steelhead trout (Oncorhynchus mykiss) and are top aquatic predators. We surveyed the density and body size distributions of D. tenebrosus and O. mykiss in a California tributary stream, combined with a field study to determine mass-specific excretion rates of ammonium (N) and total dissolved phosphorus (P) for D. tenebrosus. We estimated O. mykiss excretion rates (N, P) by bioenergetics using field-collected data on the nutrient composition of O. mykiss diets from the same system. Despite lower abundance, D. tenebrosus biomass was 2.5 times higher than O. mykiss. Mass-specific excretion summed over 170 m of stream revealed that O. mykiss recycle 1.7 times more N, and 1.2 times more P than D. tenebrosus, and had a higher N:P ratio (8.7) than that of D. tenebrosus (6.0), or the two species combined (7.5). Through simulated trade-offs in biomass, we estimate that shifts from salamander biomass toward fish biomass have the potential to ease nutrient limitation in forested tributary streams. These results suggest that natural and anthropogenic heterogeneity in the relative abundance of these vertebrates and variation in the uptake rates across river networks can affect broad-scale patterns of nutrient limitation. DOI
10. Greig, HS; Kratina, P; Thompson, PL; Palen, WJ; Richardson, JS; Shurin, JB. (2012) Warming, eutrophication, and predator loss amplify subsidies between aquatic and terrestrial ecosystems.Global Change Biology 18: 504-514 Warming, eutrophication, and predator loss amplify subsidies between aquatic and terrestrial ecosystems
allochthonous resources; amphibians; climate warming; detritus decomposition; global change; insect emergence; spatial subsidies; top-down control
The exchange of organisms and energy among ecosystems has major impacts on food web structure and dynamics, yet little is known about how climate warming combines with other pervasive anthropogenic perturbations to affect such exchanges. We used an outdoor freshwater mesocosm experiment to investigate the interactive effects of warming, eutrophication, and changes in top predators on the flux of biomass between aquatic and terrestrial ecosystems. We demonstrated that predatory fish decoupled aquatic and terrestrial ecosystems by reducing the emergence of aquatic organisms and suppressing the decomposition of terrestrial plant detritus. In contrast, warming and nutrients enhanced cross-ecosystem exchanges by increasing emergence and decomposition, and these effects were strongest in the absence of predators. Furthermore, we found that warming advanced while predators delayed the phenology of insect emergence. Our results demonstrate that anthropogenic perturbations may extend well beyond ecosystem boundaries by influencing cross-ecosystem subsidies. We find that these changes are sufficient to substantially impact recipient communities and potentially alter the carbon balance between aquatic and terrestrial ecosystems and the atmosphere. DOI
9. Kupferberg, SJ; Palen, WJ; Lind, AJ; Bobzien, S; Catenazzi, A; Drennan, J; Power, ME. (2012) Effects of Flow Regimes Altered by Dams on Survival, Population Declines, and Range-Wide Losses of California River-Breeding Frogs.Conservation Biology 26: 513-524 Effects of Flow Regimes Altered by Dams on Survival, Population Declines, and Range-Wide Losses of California River-Breeding Frogs
amphibian declines; hydropower; natural flow regime; pulsed flows; Rana boylii; Rana draytonii
Widespread alteration of natural hydrologic patterns by large dams combined with peak demands for power and water delivery during summer months have resulted in frequent aseasonal flow pulses in rivers of western North America. Native species in these ecosystems have evolved with predictable annual flood-drought cycles; thus, their likelihood of persistence may decrease in response to disruption of the seasonal synchrony between stable low-flow conditions and reproduction. We evaluated whether altered flow regimes affected 2 native frogs in California and Oregon (U.S.A.) at 4 spatial and temporal extents. We examined changes in species distribution over approximately 50 years, current population density in 11 regulated and 16 unregulated rivers, temporal trends in abundance among populations occupying rivers with different hydrologic histories, and within-year patterns of survival relative to seasonal hydrology. The foothill yellow-legged frog (Rana boylii), which breeds only in flowing water, is more likely to be absent downstream of large dams than in free-flowing rivers, and breeding populations are on average 5 times smaller in regulated rivers than in unregulated rivers. Time series data (range = 8 - 19 years) from 5 populations of yellow-legged frogs and 2 populations of California red-legged frogs (R. draytonii) across a gradient of natural to highly artificial timing and magnitude of flooding indicate that variability of flows in spring and summer is strongly correlated with high mortality of early life stages and subsequent decreases in densities of adult females. Flow management that better mimics natural flow timing is likely to promote persistence of these species and others with similar phenology. DOI
8.Palen, WJ; Schindler, DE. (2010) Water clarity, maternal behavior, and physiology combine to eliminate UV radiation risk to amphibians in a montane landscape.Proceedings of the National Academy of Sciences of the United States of America 107: 9701-9706 Water clarity, maternal behavior, and physiology combine to eliminate UV radiation risk to amphibians in a montane landscape
amphibian declines; ultraviolet radiation; risk analysis; dissolved organic matter; oviposition behavior
Increasing UV-B radiation (UV-B; 290-320 nm) due to stratospheric ozone depletion has been a leading explanation for the decline in amphibians for nearly 2 decades. Yet, the likelihood that UV-B can influence amphibians at the large spatial scales relevant to population declines has not yet been evaluated. A key limitation has been in relating results from individual sites to the effect of UV-B for populations distributed across heterogeneous landscapes. We measured critical embryonic exposures to UV-B for two species of montane amphibians with contrasting physiological sensitivities, long-toed salamander (Ambystoma macrodactylum) and Cascades frog (Rana cascadae), at field sites spanning a gradient of UV-B attenuation in water. We then used these experimental results to estimate the proportion of embryos exposed to harmful UV-B across a large number of breeding sites. By combining surveys of the incubation timing, incident UV-B, optical transparency of water, and oviposition depth and light exposure of embryos at each site, we present a comprehensive assessment of the risk posed by UV-B for montane amphibians of the Pacific Northwest. We found that only 1.1% of A. macrodactylum and no R. cascadae embryos across a landscape of breeding sites are exposed to UV-B exceeding lethal levels. These results emphasize that accurately estimating the risk posed by environmental stressors requires placing experimental results in a broader ecological context that accounts for the heterogeneity experienced by populations distributed across natural landscapes. DOI
6. Kupferberg, SJ; Catenazzi, A; Lunde, K; Lind, AJ; Palen, WJ. (2009) Parasitic Copepod (Lernaea cyprinacea) Outbreaks in Foothill Yellow-legged Frogs (Rana boylii) Linked to Unusually Warm Summers and Amphibian Malformations in Northern California.Copeia 2009: 529-537 Parasitic Copepod (Lernaea cyprinacea) Outbreaks in Foothill Yellow-legged Frogs (Rana boylii) Linked to Unusually Warm Summers and Amphibian Malformations in Northern California
CLIMATE-CHANGE; POPULATION DECLINES; RIBEIROIA INFECTION; LIMB DEVELOPMENT; DISEASE; RIVER; METAMORPHOSIS; DEFORMITIES; ECOLOGY; SIZE
How climate change may affect parasite-host assemblages and emerging Infectious diseases Is an Important question In amphibian decline research. We present data supporting a link between periods of unusually warm summer water temperatures during 2006 and 2008 In a northern California river, outbreaks of the parasitic copepod Lernaea cyprinacea, and malformations in tadpoles and young of the year Foothill Yellow-legged Frogs (Rana boylii). Relative to baseline data gathered since 1989, both 2006 and 2008 had significantly longer periods when daily mean water temperatures exceeded 20 degrees C compared to years without copepod outbreaks. Infestation varied spatially In the watershed, as prevalence Increased concomitantly with temperature along a 5.2 km longitudinal transect. At breeding sites of R. boylii with copepods in 2006, Infestation ranged from 2.9% of Individuals upstream to 58.3% downstream. In 2008, copepods were absent from the most upstream sites and Infested up to 28.6% of Individuals sampled at downstream locations. Copepods most frequently embedded near a hind limb or the cloaca. Among Individuals with parasites In 2006, 26.5% had morphological abnormalities compared to 1.1% of un-infested individuals. In 2008 when the infestation peak occurred late In development (post Gosner stage 39), abnormalities, were not associated with copepod Infestation. In both years, recently metamorphosed frogs with copepods were, on average, slightly smaller than those not Infested. These occurrences represent a sudden Increase in local prevalence atypical for this river ecosystem. Previously we had only once seen copepods on amphibians (on non-native Bullfrogs, Rana catesbeiana), six km further downstream. Pacific Chorus Frogs, Pseudocris regilla, which co-occur with R. boylii in shallow near shore habitats were not used as hosts. The data suggest that Increasing summer water temperatures, decreased daily discharge, or a combination of both, promote outbreaks of this non-native parasite on an Indigenous host, and could present a threat to the long-term conservation of R. boylii under the flow regime scenarios predicted by climate change models. DOI
5.Palen, WJ; Williamson, CE; Clauser, AA; Schindler, DE. (2005) Impact of UV-B exposure on amphibian embryos: linking species physiology and oviposition behaviour.Proceedings of the Royal Society B-Biological Sciences 272: 1227-1234 Impact of UV-B exposure on amphibian embryos: linking species physiology and oviposition behaviour
amphibian declines; ultraviolet-B radiation; photoenzymatic repair; physiology; dissolved organic matter; oviposition behaviour
Increasing ultraviolet-B radiation (UV-B) has recently captured the attention of ecologists as a key environmental stressor. Certain species may be particularly vulnerable as a result of either high natural exposure to UV-B or limited physiological capacity to withstand it. UV-B sensitivity has been examined at the cellular and individual level for a wide variety of taxa, but estimates of exposure to UV-B in natural systems are lacking and predictions of large-scale impacts are therefore limited. Here, we combine data on the physiological sensitivity to UV-B and patterns of field exposure across sites for embryos of several well-studied US Pacific Northwest amphibian species. We find substantial differences among species' physiological abilities to withstand UV-B and in the level of UV-B exposure of embryos in the field. More specifically, we find that species with the highest physiological sensitivity to UV-B are those with the lowest field exposures as a function of the location of embryos and the UV-B attenuation properties of water at each site. These results also suggest that conclusions made about species' vulnerability to UV-B in the absence of information on field exposures may often be misleading. DOI
4. Winder, M; Schindler, DE; Moore, JW; Johnson, SP; Palen, WJ. (2005) Do bears facilitate transfer of salmon resources to aquatic macroinvertebrates?Canadian Journal of Fisheries and Aquatic Sciences 62: 2285-2293 Do bears facilitate transfer of salmon resources to aquatic macroinvertebrates?
In coastal areas of the Pacific Northwest bears (Ursus spp.) prey heavily on spawning Pacific salmon (Oncorhynchus spp.) and selectively kill energy-rich individuals that are the most recent arrivals on spawning grounds. Pacific salmon eventually die in spawning habitats anyway, albeit with considerably lower energetic content. We investigated whether foraging activities of bears facilitate growth of stream invertebrates by increasing the duration of salmon carcass availability and the nutritional value of carcasses for scavengers. Our survey in southwest Alaska showed that carcasses are highly colonized by caddisfly (Trichoptera) larvae. Caddisflies show a strong preference for bear-killed over senescent carcasses, which may be a result of extended temporal availability, improved accessibility of consumable tissue, and higher energetic content of bear-killed fish. Isotope analyses further indicate uptake of marine-derived nutrients in caddisflies during the salmon run, which, however, does not extend into subsequent generations. Thus, species with life histories linked to the annual marine derived nutrient pulse gain the biggest advantage from the salmon resource subsidy. A long-term survey in several creeks in this region showed that bear predation intensity varied greatly among creeks and years, therefore indirect effects of bear predation on aquatic scavengers are likely highly patchy in time and space. DOI
2. Schindler, DE; Scheuerell, MD; Moore, JW; Gende, SM; Francis, TB; Palen, WJ. (2003) Pacific salmon and the ecology of coastal ecosystems.Frontiers in Ecology and the Environment 1: 31-37 Pacific salmon and the ecology of coastal ecosystems
One of the most spectacular phenomena in nature is the annual return of millions of salmon to spawn in their natal streams and lakes along the Pacific coast of North America. The salmon die after spawning, and the nutrients and energy in their bodies, derived almost entirely from marine sources, are deposited in the freshwater ecosystems. This represents a vital input to the ecosystems used as spawning grounds. Salmon-derived nutrients make up a substantial fraction of the plants and animals in aquatic and terrestrial habitats associated with healthy salmon populations. The decline of salmon numbers throughout much of their southern range in North America has prompted concern that the elimination of this "conveyor belt" of nutrients and energy may fundamentally change the productivity of these coastal freshwater and terrestrial ecosystems, and consequently their ability to support wildlife, including salmon. If progress is to be made towards understanding and conserving the connection between migratory salmon and coastal ecosystems, scientists and decision-makers must explore and understand the vast temporal and spatial scales that characterize this relationship. DOI
1.Palen, WJ; Schindler, DE; Adams, MJ; Pearl, CA; Bury, RB; Diamonds, SA. (2002) Optical characteristics of natural waters protect amphibians from UV-B in the US Pacific Northwest.Ecology 83: 2951-2957 Optical characteristics of natural waters protect amphibians from UV-B in the US Pacific Northwest
Ambystoma gracile; Ambystoma macrodactylum; amphibian declines; Bufo boreas; Cascades frog; dissolved organic matter, DOM; long-toed salamander; morthwestern salamander; Pacific Northwest; Rana cascadae; UV-B radiation; western toad
Increased exposure to ultraviolet-B (UV-B) radiation has been proposed as a major environmental stressor leading to global amphibian declines. Prior experimental evidence from the U.S. Pacific Northwest (PNW) indicating the acute embryonic sensitivity of at least four amphibian species to UV-B has been, central to the literature about amphibian decline. However, these results have not been expanded to address population-scale effects and natural landscape variation in UV-B transparency of water at amphibian breeding sites: both necessary links to assess the importance of UV-B for amphibian declines. We quantified the UV-B transparency of 136 potential amphibian breeding sites to establish the pattern of UV-B exposure across two montane regions in the PNW. Our data suggest that 85% of sites - are naturally proiected by dissolved organic matter in pond water, and that only a fraction of breeding sites are expected to experience UV-B intensities exceeding levels associated with elevated egg mortality. Thus, the spectral characteristics of natural waters likely mediate the physiological effects of UV-B on amphibian eggs in all but the clearest waters. These data imply that UV-B is unlikely to cause broad amphibian declines across the landscape of the American Northwest. DOI
