67. Guzman, LM; Chamberlain, SA; Elle, E. (2021) Network robustness and structure depend on the phenological characteristics of plants and pollinators.Ecol. Evol. 11: 13321-13334 Network robustness and structure depend on the phenological characteristics of plants and pollinators
mutualism; network; phenology; plant-pollinator; trait
Many structural patterns have been found to be important for the stability and robustness of mutualistic plant-pollinator networks. These structural patterns are impacted by a suite of variables, including species traits, species abundances, their spatial configuration, and their phylogenetic history. Here, we consider a specific trait: phenology, or the timing of life history events. We expect that timing and duration of activity of pollinators, or of flowering in plants, could greatly affect the species' roles within networks in which they are embedded. Using plant-pollinator networks from 33 sites in southern British Columbia, Canada, we asked (a) how phenological species traits, specifically timing of first appearance in the network and duration of activity in a network, were related to species' roles within a network, and (b) how those traits affected network robustness to phenologically biased species loss. We found that long duration of activity increased connection within modules for both pollinators and plants and among modules for plants. We also found that date of first appearance was positively related to interaction strength asymmetry in plants but negatively related to pollinators. Networks were generally more robust to the loss of pollinators than plants, and robustness increased if the models allow new interactions to form when old ones are lost, constrained by overlapping phenology of plants and pollinators. Robustness declined with the loss of late-flowering plants, which tended to have higher interaction strength asymmetry. In addition, robustness declined with loss of early-flying or long-duration pollinators. These pollinators tended to be among-module connectors. Our results point to networks being limited by early-flying pollinators. If plants flower earlier due to climate change, plant fitness may decline as they will depend on early emerging pollinators, unless pollinators also emerge earlier. DOI PubMed
66. Kelly, T; Elle, E. (2020) Effects of community composition on plant-pollinator interaction networks across a spatial gradient of oak-savanna habitats.Oecologia 193: 211-223 Effects of community composition on plant-pollinator interaction networks across a spatial gradient of oak-savanna habitats
Mutualism; Ecoregions; Modularity; Nestedness; Specialization
Distance between habitats may impact the composition and corresponding interactions between trophic levels. Mutualistic networks, such as those of plants and pollinators tend to have a core set of properties that often relate to the resilience of the community, or the ability of the community to retain function and structure after a disturbance. Furthermore, network structure is highly dependent on the number of specialists and generalists; however, it is unclear how different groups of species with various life-history strategies influence network structure. In this study, we evaluated how the composition of plants and pollinators within 16 oak-savanna sites changed across a latitudinal gradient. In addition, we evaluated how the abundance of different groups of plants and pollinators affected network metrics related to resilience. We found that the composition of plants and pollinators varied between ecoregions, while pollinator composition further varied with habitat characteristics. Network metrics displayed no spatial pattern but were related to the abundance of several pollinator groups. Above-ground nesting insects had a positive relationship with nestedness and a negative relationship with modularity, while predatory larvae had a negative relationship with modularity. Thus, above-ground nesting insects and predatory larvae could be expected to increase network resilience. This study emphasizes how spatial scales can influence species compositions, which in turn affects the structure of interactions in the community with implications for resilience. DOI PubMed
65. Kelly, TT; Elle, E. (2020) Investigating bee dietary preferences along a gradient of floral resources: how does resource use align with resource availability?Insect Sci.Investigating bee dietary preferences along a gradient of floral resources: how does resource use align with resource availability?
andrenidae; dietary breadth; ecoregions; oak-savanna; pollen; specialization
Bee dietary preferences, or the floral resources that they consistently collect, likely impact where a species can persist. For this reason it is likely that bee dietary preferences are dependent upon the composition of the plant community. In this study, we evaluated floral visits and pollen loads of the mining bee,Andrena angustitarsataViereck, across a 630 km north-south range to understand dietary preferences along a floral resource gradient. Previous research, in a more geographically limited area, suggested this species was an eclectic oligolege on predominantly Apiaceae and in part Rosaceae. In the present study we found the species predominately visited and collected pollen from Apiaceae and Rosaceae, but visited 12 flower families and collected pollen from 32, distinguishing them as generalist foragers. The frequency of Apiaceae pollen on the bees and the species-level specialization index (a measure of visit specialization) were higher in regions with higher Apiaceae abundance. In addition Apiaceae and Rosaceae were the only plant families significantly preferred for pollen collection, regardless of floral abundance. We conclude that across our study regionA. angustitarsatahas a generalist dietary breadth, but also has dietary preference for Apiaceae and Rosaceae. Our study indicates that while bees may overall make generalist foraging decisions they may still prefer and likely benefit from selecting fewer flower taxa. DOI PubMed
64. Reilly, JR; Artz, DR; Biddinger, D; Bobiwash, K; Boyle, NK; Brittain, C; Brokaw, J; Campbell, JW; Daniels, J; Elle, E; Ellis, JD; Fleischer, SJ; Gibbs, J; Gillespie, RL; Gundersen, KB; Gut, L; Hoffman, G; Joshi, N; Lundin, O; Mason, K; McGrady, CM; Peterson, SS; Pitts-Singer, TL; Rao, S; Rothwell, N; Rowe, L; Ward, KL; Williams, NM; Wilson, JK; Isaacs, R; Winfree, R. (2020) Crop production in the USA is frequently limited by a lack of pollinators: Pollination limitation in US crops.Proc. R. Soc. B-Biol. Sci. 287 Crop production in the USA is frequently limited by a lack of pollinators: Pollination limitation in US crops
pollination limitation; economic value; wild bees; crop yield; ecosystem services; honeybee
Most of the world's crops depend on pollinators, so declines in both managed and wild bees raise concerns about food security. However, the degree to which insect pollination is actually limiting current crop production is poorly understood, as is the role of wild species (as opposed to managed honeybees) in pollinating crops, particularly in intensive production areas. We established a nationwide study to assess the extent of pollinator limitation in seven crops at 131 locations situated across major crop-producing areas of the USA. We found that five out of seven crops showed evidence of pollinator limitation. Wild bees and honeybees provided comparable amounts of pollination for most crops, even in agriculturally intensive regions. We estimated the nationwide annual production value of wild pollinators to the seven crops we studied at over $1.5 billion; the value of wild bee pollination of all pollinator-dependent crops would be much greater. Our findings show that pollinator declines could translate directly into decreased yields or production for most of the crops studied, and that wild species contribute substantially to pollination of most study crops in major crop-producing regions.Website DOI
63. Rammell, NF; Gillespie, SD; Elle, E. (2019) Visiting insect behaviour and pollen transport for a generalist oak-savannah wildflower, Camassia quamash (Asparagaceae).Can. Entomol. 151 Visiting insect behaviour and pollen transport for a generalist oak-savannah wildflower, Camassia quamash (Asparagaceae)
Many studies have investigated plant-pollinator interactions using visit records of insects contacting floral reproductive organs. However, these studies may not reflect the effectiveness of visits, since factors such as visitor behaviour and the composition of pollen on their bodies may influence conspecific pollen transfer required for fertilisation in plants. Here we study how pollen transport to a generalist wildflower, Camassia quamash (Pursh) Greene (Asparagaceae), is influenced by the behaviour and body pollen of five functional visitor groups (Andrena Fabricius (Hymenoptera: Andrenidae)/Halictidae (Hymenoptera), Apis mellifera Linnaeus (Hymenoptera: Apidae), Bombus Latreille (Hymenoptera: Apidae), Osmia Panzer (Hymenoptera: Megachilidae), and Syrphidae (Diptera). We found that functional visitor groups differed in their behaviour (Bombus and Osmia were legitimate visitors, contacting both anthers and stigmas) and in the amount of conspecific pollen on their bodies (A. mellifera had the highest levels and Andrena/Halictidae the lowest). Conspecific pollen receipt by C. quamash stigmas was high (>80%), and best explained by visitor behaviour rather than the proportion of visitors with high amounts of conspecific body pollen. Our findings highlight the utility of pollen analyses for understanding pollinator effectiveness. DOI
62. Toshack, M; Elle, E. (2019) Wild bumble bee foraging preferences and fat content in highbush blueberry agro-ecosystems.Apidologie 50: 425-435 Wild bumble bee foraging preferences and fat content in highbush blueberry agro-ecosystems
Bombus; pollen analysis; pollinator body condition; Vaccinium corymbosum
Agricultural intensification can impact the availability and quality of resources. We analyzed resource use by bumble bees (Bombus spp.), important pollinators of highbush blueberry (Vaccinium corymbosum), collected from conventional highbush blueberry farms, organic highbush blueberry farms, and nearby natural areas in the lower Fraser River valley of British Columbia, Canada. We identified corbicular pollen and measured bee fat content as an indicator of body condition. Bumble bees use non-crop resources, including pollen from plant species not found on farms. Bees from natural areas had higher pollen protein content in corbicular pollen and higher body fat content than those from conventional and organic farms. There was no difference between farm types, and we could not demonstrate a relationship between pollen protein and bee fat content. Our findings illustrate the importance of resource availability throughout agro-ecological landscapes, including not only farms but also off-farm areas. DOI
61. Bishop, CA; Moran, AJ; Toshack, MC; Elle, E; Maisonneuve, F; Elliott, JE. (2018) Hummingbirds and bumble bees exposed to neonicotinoid and organophosphate insecticides in the Fraser Valley, British Columbia, Canada.Environ. Toxicol. Chem. 37 Hummingbirds and bumble bees exposed to neonicotinoid and organophosphate insecticides in the Fraser Valley, British Columbia, Canada
Pesticides; Wildlife toxicology; Contaminants of emerging concern; Biomonitoring; Neonicotinoid; Birds; Bees
To measure exposure to neonicotinoid and other pesticides in avian pollinators, we made novel use of cloacal fluid and fecal pellets from rufous (Selasphorus rufus) and Anna's (Calypte anna) hummingbirds living near blueberry fields in the Fraser River Valley and Vancouver Island, British Columbia, Canada. To examine on-farm exposure to pesticides in invertebrate pollinators, we also collected bumble bees native to Canada (Bombus mixtus, Bombus flavifrons, and Bombus melanopygus), their pollen, and blueberry leaves and flowers from within conventionally sprayed and organic blueberry farms. By sites and sample type, the results reported in the present study represent pooled samples (n=1). In 2015 to 2016, the combined concentration of the neonicotinoid insecticides imidacloprid, thiamethoxam, and clothianidin detected in hummingbird cloacal fluid from sites near conventionally sprayed blueberry fields was 3.63ng/mL (ppb). Among the 18 compounds measured in fecal pellets, including one neonicotinoid (imidacloprid), only piperonyl butoxide was detected (1.47-5.96ng/g). Piperonyl butoxide is a cytochrome P450 inhibitor applied with some insecticides to increase their toxic efficacy. Only diazinon was detected in bumble bees (0.197ng/g), whereas diazinon (1.54-1.7ng/g) and imidacloprid (up to 18.4ng/g) were detected in pollen collected from bumble bees including the bees from organic sites located near conventionally sprayed blueberry farms. Imidacloprid was also detected at 5.16ng/g in blueberry flowers collected 1 yr post spray from 1 of 6 conventionally sprayed blueberry farms. Environ Toxicol Chem 2018;37:2143-2152. (c) 2018 SETAC DOI PubMed
60. Bobiwash, K; Uriel, Y; Elle, E. (2018) Pollen Foraging Differences Among Three Managed Pollinators in the Highbush Blueberry (Vaccinium corymbosum) Agroecosystem.J. Econ. Entomol. 111 Pollen Foraging Differences Among Three Managed Pollinators in the Highbush Blueberry (Vaccinium corymbosum) Agroecosystem
agricultural entomology; agriculture; berry crop insect; pollination; ecology and behavior
Highbush blueberry, Vaccinium corymbosum (Gray), production in British Columbia is dependent upon insect pollination for fruit yield with particular cultivars demonstrating low yields due to poor pollination. New managed species of pollinators are being developed to provide farmers with managed pollinator options beyond Apis mellifera (Linnaeus). Pollinators in highbush blueberry agricultural systems encounter a variety of nontarget floral resources that may affect the pollination received by the crop. Our study analyzed the differences in pollen foraging of honey bees and two species of managed bumblebees across nine farm sites. Corbicular pollen loads from pollen foraging workers were removed and identified to the lowest taxonomic level possible. Of the three managed pollinators, the corbicular pollen loads of Bombus huntii (Greene) contained the most blueberry pollen (52.1%), three times as much as the two other managed bee species. Fifteen morphotypes of pollen were identified from all foraging workers with Rosaceae being the most frequently gathered overall pollen type (n = 74). The noncrop pollen identified in our samples derived from plant species not common as weedy species in the agroecosystem suggesting that floral resource diversity outside of the farm boundaries is important to pollinators. The three managed species in our blueberry fields utilized floral resources differentially underscoring the importance of pollinator species' characteristics and large-scale floral resource landscape in developing new managed pollinators and pollination strategies. DOI PubMed
59. Gillespie, S; Elle, E. (2018) Non-native plants affect generalist pollinator diet overlap and foraging behavior indirectly, via impacts on native plant abundance.Biol. Invasions 20 Non-native plants affect generalist pollinator diet overlap and foraging behavior indirectly, via impacts on native plant abundance
Behavioral plasticity; Competition; Invasive; Bombus; Pollination
Flowering invasive plants can have dramatic effects on the resource landscape available to pollinators. Because many pollinators exhibit behavioral plasticity in response to competitor or resource density, this in turn can result in impacts on ecological processes such as pollination and plant reproduction. We examine how interactions between five common generalist eusocial bees change across an invasion gradient by examining how bee abundance and diet overlap changed with variation in both invasive plant abundance and competitor abundance in a temperate oak-savannah ecosystem. Specifically we focus on the bumblebees Bombus bifarius, B. mixtus, B. melanopygus and B. vosnesenskii, as well as the non-native honeybee Apis mellifera, and their interactions with the native flowering plants Camassia quamash, Camassia liechtlinii, and the invasive shrub Cytisus scoparius. We further examine whether changes in pollinator visits to the invasive and two common native plants can explain changes in diet overlap. Abundance of the invasive plant and other common floral resources had strong impacts on focal bee abundance, with certain species more likely to be present at highly invaded sites. This may be because highly invaded sites tended to be embedded in forested landscapes where those bees are common. Diet overlap was most affected by abundance of a common native plant, rather than the invasive plant, with diet overlap increasing non-linearly with abundance of the native plant. Furthermore, Apis mellifera, did not appear to have direct competitive effects on native bumblebees in this habitat. However, visit patterns suggest that bees most abundant at highly invaded sites may compete for access to native resources. Thus the impacts of this invasive plant on our focal bee species may be primarily indirect, via its' competitive effects on native plants. DOI
58. Gillespie, SD; Bayley, J; Elle, E. (2017) Native bumble bee (Hymenoptera: Apidae) pollinators vary in floral resource use across an invasion gradient.Canadian Entomologist 149: 204-213 Native bumble bee (Hymenoptera: Apidae) pollinators vary in floral resource use across an invasion gradient
Integration of pollinator-dependent invasive plants into native pollination networks can have direct and indirect effects on local plant and pollinator communities. Impacts on local plants are well documented; however effects on native pollinators have gained less attention. We examine these issues in habitat fragments of the endangered oak-savannah ecosystem in British Columbia, Canada. We measured pollen collection by native bumble bees (Bombus Latreille; Hymenoptera: Apidae) and the introduced honey bee (Apis mellifera Linnaeus; Hymenoptera: Apidae) foraging on two common native plants in habitat fragments with varying invasive (Cytisus scoparius (Linnaeus) Link; Fabaceae) density. The Bombus species with the largest workers had higher proportions of invasive pollen on their bodies and in their corbiculae than smaller workers. Honey bees rarely collected C. scoparius pollen. While some native bumble bees species collect an increasing proportion of C. scoparius pollen with increasing C. scoparius density, this did not translate into an increased potential for pollination. Rather, measures of effective pollination decline with C. scoparius density. Overall, our results suggest that some bee species may be better at finding resources at highly invaded sites. Apis mellifera is likely not playing a major role in facilitating the spread of C. scoparius in our region. Rather C. scoparius is visited by a complement of native bumble bees that are similar to pollinators in the native range of this plant. DOI
57. Lichtenberg, EM; Kennedy, CM; Kremen, C; Batary, P; Berendse, F; Bommarco, R; Bosque-Perez, NA; Carvalheiro, LG; Snyder, WE; Williams, NM; Winfree, R; Klatt, BK; Astrom, S; Benjamin, F; Brittain, C; Chaplin-Kramer, R; Clough, Y; Danforth, B; Diekotter, T; Eigenbrode, SD; Ekroos, J; Elle, E; Freitas, BM; Fukuda, Y; Gaines-Day, HR; Grab, H; Gratton, C; Holzschuh, A; Isaacs, R; Isaia, M; Jha, S; Jonason, D; Jones, VP; Klein, AM; Krauss, J; Letourneau, DK; Macfadyen, S; Mallinger, RE; Martin, EA; Martinez, E; Memmott, J; Morandin, L; Neame, L; Otieno, M; Park, MG; Pfiffner, L; Pocock, MJO; Ponce, C; Potts, SG; Poveda, K; Ramos, M; Rosenheim, JA; Rundlof, M; Sardinas, H; Saunders, ME; Schon, NL; Sciligo, AR; Sidhu, CS; Steffan-Dewenter, I; Tscharntke, T; Vesely, M; Weisser, WW; Wilson, JK; Crowder, DW. (2017) A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes.Global Change Biology 23: 4946-4957 A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes
agricultural management schemes; arthropod diversity; biodiversity; evenness; functional groups; landscape complexity; meta-analysis; organic farming; plant diversity
Agricultural intensification is a leading cause of global biodiversity loss, which can reduce the provisioning of ecosystem services in managed ecosystems. Organic farming and plant diversification are farm management schemes that may mitigate potential ecological harm by increasing species richness and boosting related ecosystem services to agroecosystems. What remains unclear is the extent to which farm management schemes affect biodiversity components other than species richness, and whether impacts differ across spatial scales and landscape contexts. Using a global metadataset, we quantified the effects of organic farming and plant diversification on abundance, local diversity (communities within fields), and regional diversity (communities across fields) of arthropod pollinators, predators, herbivores, and detritivores. Both organic farming and higher in-field plant diversity enhanced arthropod abundance, particularly for rare taxa. This resulted in increased richness but decreased evenness. While these responses were stronger at local relative to regional scales, richness and abundance increased at both scales, and richness on farms embedded in complex relative to simple landscapes. Overall, both organic farming and in-field plant diversification exerted the strongest effects on pollinators and predators, suggesting these management schemes can facilitate ecosystem service providers without augmenting herbivore (pest) populations. Our results suggest that organic farming and plant diversification promote diverse arthropod metacommunities that may provide temporal and spatial stability of ecosystem service provisioning. Conserving diverse plant and arthropod communities in farming systems therefore requires sustainable practices that operate both within fields and across landscapes. DOI
56. Moeller, DA; Runquist, RDB; Moe, AM; Geber, MA; Goodwillie, C; Cheptou, PO; Eckert, CG; Elle, E; Johnston, MO; Kalisz, S; Ree, RH; Sargent, RD; Vallejo-Marin, M; Winn, AA. (2017) Global biogeography of mating system variation in seed plants.Ecology Letters 20: 375-384 Global biogeography of mating system variation in seed plants
Biotic interactions; breeding system; floral evolution; latitudinal gradient; life history; outcrossing; plant-pollinator interaction; pollination; self-fertilisation; sexual system
Latitudinal gradients in biotic interactions have been suggested as causes of global patterns of biodiversity and phenotypic variation. Plant biologists have long speculated that outcrossing mating systems are more common at low than high latitudes owing to a greater predictability of plant-pollinator interactions in the tropics; however, these ideas have not previously been tested. Here, we present the first global biogeographic analysis of plant mating systems based on 624 published studies from 492 taxa. We found a weak decline in outcrossing rate towards higher latitudes and among some biomes, but no biogeographic patterns in the frequency of self-incompatibility. Incorporating life history and growth form into biogeographic analyses reduced or eliminated the importance of latitude and biome in predicting outcrossing or self-incompatibility. Our results suggest that biogeographic patterns in mating system are more likely a reflection of the frequency of life forms across latitudes rather than the strength of plant-pollinator interactions. DOI
55. Elwell, SL; Griswold, T; Elle, E. (2016) Habitat type plays a greater role than livestock grazing in structuring shrubsteppe plant-pollinator communities.Journal of Insect Conservation 20: 515-525 Habitat type plays a greater role than livestock grazing in structuring shrubsteppe plant-pollinator communities
Biodiversity; Community composition; Insect conservation; Livestock grazing; Pollinators; Shrubsteppe
Livestock grazing is a widespread grassland disturbance and can negatively impact biodiversity. Pollinators constitute a vital component of grassland ecosystems, but the impact of grazing on pollinator diversity has seldom been evaluated in North America. We assessed vegetation structure, and pollinator and flowering plant abundance, richness, diversity, and community composition in four pairs of spring-grazed/ungrazed sites in south-central British Columbia, Canada. We also investigated whether pollinator or floral communities differed between the two threatened shrubsteppe habitat types we sampled-antelope-brush and big sagebrush shrubsteppe. Pan-trapping surveys captured 5907 bees, flies, beetles, wasps and butterflies constituting 253 species. We found that the percent cover of shrubs and bare soil increased with grazing, while the height of grasses and forbs decreased. In contrast, pollinator and flowering plant abundance, richness, diversity, and community composition were not significantly affected by grazing. Flowering plant and pollinator community composition did differ significantly between shrubsteppe habitats. Our results indicate that grasslands in North America, when managed responsibly, can maintain pollinator and flowering plant diversity under grazing pressure. The continued effort of land managers to balance ecological integrity and economic viability will be important for the conservation of grassland pollination systems. DOI
54. Gibbs, J; Elle, E; Bobiwash, K; Haapalainen, T; Isaacs, R. (2016) Contrasting Pollinators and Pollination in Native and Non-Native Regions of Highbush Blueberry Production.PLoS One 11 Contrasting Pollinators and Pollination in Native and Non-Native Regions of Highbush Blueberry Production
Highbush blueberry yields are dependent on pollination by bees, and introduction of managed honey bees is the primary strategy used for pollination of this crop. Complementary pollination services are also provided by wild bees, yet highbush blueberry is increasingly grown in regions outside its native range where wild bee communities may be less adapted to the crop and growers may still be testing appropriate honey bee stocking densities. To contrast crop pollination in native and non-native production regions, we sampled commercial 'Bluecrop' blueberry fields in British Columbia and Michigan with grower-selected honey bee stocking rates (0-39.5 hives per ha) to compare bee visitors to blueberry flowers, pollination and yield deficits, and how those vary with local-and landscape-scale factors. Observed and Chao-1 estimated species richness, as well as Shannon diversity of wild bees visiting blueberries were significantly higher in Michigan where the crop is within its native range. The regional bee communities were also significantly different, with Michigan farms having greater dissimilarity than British Columbia. Blueberry fields in British Columbia had fewer visits by honey bees than those in Michigan, irrespective of stocking rate, and they also had lower berry weights and a significant pollination deficit. In British Columbia, pollination service increased with abundance of wild bumble bees, whereas in Michigan the abundance of honey bees was the primary predictor of pollination. The proportion of seminatural habitat at local and landscape scales was positively correlated with wild bee abundance in both regions. Wild bee abundance declined significantly with distance from natural borders in Michigan, but not in British Columbia where large-bodied bumble bees dominated the wild bee community. Our results highlight the varying dependence of crop production on different types of bees and reveal that strategies for pollination improvement in the same crop can vary greatly across production regions. DOI
52. Kleijn, D; Winfree, R; Bartomeus, I; Carvalheiro, LG; Henry, M; Isaacs, R; Klein, AM; Kremen, C; M'Gonigle, LK; Rader, R; Ricketts, TH; Williams, NM; Adamson, NL; Ascher, JS; Baldi, A; Batary, P; Benjamin, F; Biesmeijer, JC; Blitzer, EJ; Bommarco, R; Brand, MR; Bretagnolle, V; Button, L; Cariveau, DP; Chifflet, R; Colville, JF; Danforth, BN; Elle, E; Garratt, MPD; Herzog, F; Holzschuh, A; Howlett, BG; Jauker, F; Jha, S; Knop, E; Krewenka, KM; Le Feon, V; Mandelik, Y; May, EA; Park, MG; Pisanty, G; Reemer, M; Riedinger, V; Rollin, O; Rundlof, M; Sardinas, HS; Scheper, J; Sciligo, AR; Smith, HG; Steffan-Dewenter, I; Thorp, R; Tscharntke, T; Verhulst, J; Viana, BF; Vaissiere, BE; Veldtman, R; Westphal, C; Potts, SG. (2015) Delivery of crop pollination services is an insufficient argument for wild pollinator conservation.Nature Communications 6 Delivery of crop pollination services is an insufficient argument for wild pollinator conservation
There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost- effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost- effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments. DOI
51. Wray, JC; Elle, E. (2015) Flowering phenology and nesting resources influence pollinator community composition in a fragmented ecosystem.Landscape Ecology 30: 261-272 Flowering phenology and nesting resources influence pollinator community composition in a fragmented ecosystem
Habitat fragmentation; Oak-savannah; Landscape matrix; Community composition; Flowering plants; Nesting resources
Habitat loss is the leading cause of extinctions on the planet. However, negative effects of habitat loss and fragmentation on biodiversity can be reduced if resources in urban or semi-natural areas in the surrounding matrix can be used by wildlife. We investigated the influence of floral and nesting resources in urban- and forest-associated oak-savannah fragments, surrounding urban and forest matrix, and urban areas spatially independent from oak-savannah habitat on pollinator community composition in a fragmented oak-savannah ecosystem. Both independent urban and urban matrix sites supported high abundance and richness of plants and pollinators relative to other fragment categories, especially towards the end of the season when plants and pollinators in oak-savannah fragments were scarce. A species of particular conservation concern in our region, Bombus occidentalis, was supported by late-flowering resources in our urban sites. Forest-associated oak-savannah fragments were missing late-season species while urban-associated fragments supported high abundance and richness of mid- to late-season pollinators, likely due to supplemental use of floral resources in the urban matrix. Female cavity-nesting and ground-nesting bees were not restricted by the availability of natural nesting resources we expected them to require (e.g. small cavities, bare soil). These results provide important information on native pollinators in a highly fragmented habitat, and suggest that we should consider matrix quality in conservation planning. DOI
50. Button, L; Elle, E. (2014) Wild bumble bees reduce pollination deficits in a crop mostly visited by managed honey bees.Agriculture Ecosystems & Environment 197: 255-263 Wild bumble bees reduce pollination deficits in a crop mostly visited by managed honey bees
Pollination deficit; Edge effect; Mixed pollinator strategy; Apis mellifera; Bombus; Blueberry
We assessed the pollinator community of two cultivars of highbush blueberry (Vaccinium corymbosum, Duke and Bluecrop), and determined the importance of different pollinators to overall crop yield by measuring pollination deficits. The importance of distance to putative wild pollinator habitat (natural field edges) for pollinator abundance within fields and crop yield was also considered. Managed honey bees made 70% of flower visits (85% to Duke, 49% to Bluecrop). Wild bumble bees made half of the visits to Bluecrop. Though bumble bees were observed less frequently as distance from the natural edge increased, there was no effect of distance on levels of crop pollination. Pollination deficits were less pronounced in Duke than Bluecrop, with maximum (hand) pollination leading to a 12% (Duke) to 23% (Bluecrop) increase in yield. Exclusion of pollinators reduced yield by 50-80% compared to ambient pollination. For both cultivars, pollination deficits declined most strongly with either increasing bumble bee visits or increasing total visits (honey bees and bumble bees combined), and in no case were deficit levels significantly reduced by honey bees alone. This study supports a growing body of literature that suggests managed honey bees alone cannot reduce deficits, and that wild pollinators are needed to maximize yields in pollinator-dependent agricultural systems. (C) 2014 Elsevier B.V. All rights reserved. DOI
49. Chamberlain, S; Vazquez, DP; Carvalheiro, L; Elle, E; Vamosi, JC. (2014) Phylogenetic tree shape and the structure of mutualistic networks.Journal of Ecology 102: 1234-1243 Phylogenetic tree shape and the structure of mutualistic networks
connectance; diversity; modularity; nestedness; network structure; phylogeny imbalance; plant population and community dynamics; plant-pollinator interactions
1. Species community composition is known to alter the network of interactions between two trophic levels, potentially affecting its functioning (e. g. plant pollination success) and the stability of communities. Phylogenies vary in shape with regard to the rate of evolutionary change across a tree (influencing tree balance) and variation in the timing of branching events (affecting the distribution of node ages in trees), both of which may influence the structure of species interaction networks. Because related species are likely to share many of the traits that regulate interactions, the shape of phylogenetic trees may provide some insights into the distribution of traits within communities, and hence the likelihood of interaction among species. However, little attention has been paid to the potential effects of changes in phylogenetic diversity (PD) on interaction networks. 2. Phylogenetic diversity is influenced by species diversity within a community, but also how distantly-related the constituent species are from one another. Here, we evaluate the relationship between two important measures of phylogenetic diversity (tree shape and age of nodes) and the structure of plant-pollinator interaction networks using empirical and simulated data. Whereas the former allows us to evaluate patterns in real communities, the latter allows us to evaluate more systematically the relationship between tree shape and network structure under three different models of trait evolution. 3. In empirical networks, less balanced plant phylogenies were associated with lower connectance in interaction networks indicating that communities with the descendants of recent radiations are more diverged and specialized in their partnerships. In simulations, tree balance and the distribution of nodes through time were included in the best models for modularity, and the second best models for connectance and nestedness. In models assuming random evolutionary change through time (i.e. Brownian motion), less balanced trees and trees with nodes near the tips exhibited greater modularity, whereas in models with an early burst of radiation followed by relative stasis (i.e. early-burst models) more balanced trees and trees with nodes near roots had greater modularity. 4. Synthesis. Overall, these results suggest that the shape of phylogenies can influence the structure of plant-pollinator interaction networks. However, the mismatch between simulations and empirical data indicate that no simple model of trait evolution mimics that observed in real communities. DOI
48. Chamberlain, SA; Cartar, RV; Worley, AC; Semmler, SJ; Gielens, G; Elwell, S; Evans, ME; Vamosi, JC; Elle, E. (2014) Traits and phylogenetic history contribute to network structure across Canadian plant-pollinator communities.Oecologia 176: 545-556 Traits and phylogenetic history contribute to network structure across Canadian plant-pollinator communities
Mutualism; Interaction webs; Trophic levels; Morphological trait; Functional trait
Interaction webs, or networks, define how the members of two or more trophic levels interact. However, the traits that mediate network structure have not been widely investigated. Generally, the mechanism that determines plant-pollinator partnerships is thought to involve the matching of a suite of species traits (such as abundance, phenology, morphology) between trophic levels. These traits are often unknown or hard to measure, but may reflect phylogenetic history. We asked whether morphological traits or phylogenetic history were more important in mediating network structure in mutualistic plant-pollinator interaction networks from Western Canada. At the plant species level, sexual system, growth form, and flower symmetry were the most important traits. For example species with radially symmetrical flowers had more connections within their modules (a subset of species that interact more among one another than outside of the module) than species with bilaterally symmetrical flowers. At the pollinator species level, social species had more connections within and among modules. In addition, larger pollinators tended to be more specialized. As traits mediate interactions and have a phylogenetic signal, we found that phylogenetically close species tend to interact with a similar set of species. At the network level, patterns were weak, but we found increasing functional trait and phylogenetic diversity of plants associated with increased weighted nestedness. These results provide evidence that both specific traits and phylogenetic history can contribute to the nature of mutualistic interactions within networks, but they explain less variation between networks. DOI PubMed
47. Gielens, G; Gillespie, S; Neame, L; Elle, E. (2014) Pollen limitation is uncommon in an endangered oak savannah ecosystem.Botany 92: 743-748 Pollen limitation is uncommon in an endangered oak savannah ecosystem
pollen limitation; pollination; pollinator assemblage; pollinator diversity
Pollen receipt limits reproduction in many plants, potentially affecting population viability and trait evolution. Despite considerable research, there is little consensus on the causes of pollen limitation (PL). Reviews suggest spatial and temporal variation in PL may be important for plant reproductive fitness, yet few studies have examined PL in multiple species across sites and years. We examined how pollinator communities affected PL in six wildflower species across six sites and 2 years. Although our study was conducted in a fragmented ecosystem and on perennial species (both are associated with PL in meta-analyses), we found that PL was uncommon. The degree of PL was highly variable among years, sites, and species, with no species or site showing consistent PL. Variation in PL among sites and years was not explained by variation in diversity or visit rate of the pollinating fauna. The rarity of PL in this study may limit our assessment of the importance of pollinators, but our results do suggest that PL is highly context-dependent, which should be a focus for future work. DOI
46. Wray, JC; Neame, LA; Elle, E. (2014) Floral resources, body size, and surrounding landscape influence bee community assemblages in oak-savannah fragments.Ecological Entomology 39: 83-93 Floral resources, body size, and surrounding landscape influence bee community assemblages in oak-savannah fragments
Bees; community composition; floral resources; habitat fragmentation; landscape matrix; species traits
1. Fragmentation of natural habitats due to urban development is predicted to have negative impacts on species diversity. The surrounding landscape (or matrix') of urban or semi-natural habitats can sometimes support biodiversity, but the amount of support will depend on species-specific traits, and on the resources available in the fragment and the matrix. Using data on bees collected from 19 oak-savannah fragments, the question of whether bee communities differ when fragments are embedded in different landscapes (Douglas-fir forest vs. urban residential neighbourhoods) was investigated, and also whether these differences could be attributed to species-specific traits of bees (e.g. body size, specialization) and/or within-fragment floral resources. No differences were found in overall richness or abundance of bees, but there were distinct differences in plant and bee community composition between matrix types. Common wood-nesters and late-flying, small-bodied bees tended to be found in urban-associated fragments, which also had a lower availability of within-fragment floral resources. Forest-associated fragments, on the other hand, had a greater density and richness of early-flowering native plant species, and supported a higher abundance of large-bodied bee species. Bumble bee abundance, in particular, increased with increasing proportion of forest cover in the surrounding landscape. Large-bodied bees appear to respond to increased availability of within-fragment floral resources, but it was also hypothesised that nesting and floral resources in matrix habitat drive the differences in bee community assemblages. DOI
45. Courcelles, DMM; Button, L; Elle, E. (2013) Bee visit rates vary with floral morphology among highbush blueberry cultivars (Vaccinium corymbosum L.).Journal of Applied Entomology 137: 693-701 Bee visit rates vary with floral morphology among highbush blueberry cultivars (Vaccinium corymbosum L.)
BUMBLE BEES; POLLINATION SYNDROMES; HYMENOPTERA; ERICACEAE; ABUNDANCE; TRAITS; SIZE; PATTERNS; PLANTS; EVOLUTION
As the human population has increased, so too has the demand for biotically pollinated crops. Bees (Apoidea) are essential for pollen transfer and fruit production in many crops, and their visit patterns can be influenced by floral morphology. Here, we considered the role of floral morphology on visit rates and behaviour of managed honey bees (Apis mellifera) and wild bumble bees (genus Bombus), for four highbush blueberry cultivars (Vaccinium corymbosum L.). We measured five floral traits for each cultivar, finding significant variation among cultivars. Corolla throat diameter may be the main morphological determinant of visit rates of honey bees, which is significantly higher on the wider flowers of cv. Duke' than on Bluecrop' or Draper'. Honey bees also visited cv. Duke' legitimately but were frequent nectar robbers on the long, narrow flowers of cv. Bluecrop'. Bumble bees were infrequent (and absent on cv. Draper') but all observed visits were legitimate. Crop yield was highest for the cultivar with the highest combined (honey bee + bumble bee) visit rate, suggesting that aspects of floral morphology that affect pollinator visit patterns should be considered in crop breeding initiatives. DOI
44. Kennedy, CM; Lonsdorf, E; Neel, MC; Williams, NM; Ricketts, TH; Winfree, R; Bommarco, R; Brittain, C; Burley, AL; Cariveau, D; Carvalheiro, LG; Chacoff, NP; Cunningham, SA; Danforth, BN; Dudenhoffer, JH; Elle, E; Gaines, HR; Garibaldi, LA; Gratton, C; Holzschuh, A; Isaacs, R; Javorek, SK; Jha, S; Klein, AM; Krewenka, K; Mandelik, Y; Mayfield, MM; Morandin, L; Neame, LA; Otieno, M; Park, M; Potts, SG; Rundlof, M; Saez, A; Steffan-Dewenter, I; Taki, H; Viana, BF; Westphal, C; Wilson, JK; Greenleaf, SS; Kremen, C. (2013) A global quantitative synthesis of local and landscape effects on wild bee pollinators in agroecosystems.Ecology Letters 16: 584-599 A global quantitative synthesis of local and landscape effects on wild bee pollinators in agroecosystems
DIFFERENT SPATIAL SCALES; AGRICULTURAL LANDSCAPES; CROP POLLINATION; ECOSYSTEM SERVICES; SPECIES RICHNESS; NATIVE BEES; BIODIVERSITY; INTENSIFICATION; CONTEXT; METAANALYSIS
Bees provide essential pollination services that are potentially affected both by local farm management and the surrounding landscape. To better understand these different factors, we modelled the relative effects of landscape composition (nesting and floral resources within foraging distances), landscape configuration (patch shape, interpatch connectivity and habitat aggregation) and farm management (organic vs. conventional and local-scale field diversity), and their interactions, on wild bee abundance and richness for 39 crop systems globally. Bee abundance and richness were higher in diversified and organic fields and in landscapes comprising more high-quality habitats; bee richness on conventional fields with low diversity benefited most from high-quality surrounding land cover. Landscape configuration effects were weak. Bee responses varied slightly by biome. Our synthesis reveals that pollinator persistence will depend on both the maintenance of high-quality habitats around farms and on local management practices that may offset impacts of intensive monoculture agriculture. DOI
43. Neame, LA; Griswold, T; Elle, E. (2013) Pollinator nesting guilds respond differently to urban habitat fragmentation in an oak-savannah ecosystem.Insect Conservation and Diversity 6: 57-66 Pollinator nesting guilds respond differently to urban habitat fragmentation in an oak-savannah ecosystem
FLOWER-VISITING INSECTS; BEE COMMUNITIES; LANDSCAPE CONTEXT; TROPICAL COUNTRYSIDE; FORAGING RANGES; DIVERSITY; HYMENOPTERA; BIODIVERSITY; RESOURCES; CONSERVATION Bees;biodiversity;habitat fragmentation;nesting guilds;oak-savannah ecosystem;pollination
. 1. Habitat fragmentation is thought to threaten biodiversity, but the response of pollinators to fragmentation is still poorly understood, and research seldom includes pollinator nesting requirements. 2. We investigated pollinator community composition in a highly fragmented oak-savannah ecosystem in south-western British Columbia, Canada. We sampled pollinators in 19 fragments ranging from 0.3 to 31 ha and surrounded by a variety of land-use types, including forest, low-density suburban, and urban neighbourhoods. Pan-trapping and netting surveys captured 4464 bees, flies, and wasps in 138 species and 48 genera. 3. Contrary to expectations, overall species richness did not increase with fragment size. However, ground-nester abundance (not diversity) and cavity-nester diversity (not abundance) were higher in larger fragments, as expected. Floral richness and abundance did not foster pollinator diversity for either guild. Brood parasite responses were complex: host availability (ground-nesting bees) was generally important, richness and abundance increased in fragments with high surrounding road density, and abundance also increased in fragments with other habitat fragments nearby. 4. Responses of different nesting guilds to fragmentation may be related to their use of the landscape surrounding habitat fragments. Some common cavity nesters can nest in fences and gardens, but urban land use may be less hospitable for ground nesters. Brood parasites apparently respond both to host availability and landscape characteristics associated with movement among fragments. 5. Consideration of nesting requirements of pollinators provided some insight into their response to habitat loss in our analysis and should be considered in future studies of fragmentation impacts on pollinator biodiversity. DOI
42. Davila, YC; Elle, E; Vamosi, JC; Hermanutz, L; Kerr, JT; Lortie, CJ; Westwood, AR; Woodcock, TS; Worley, AC. (2012) Ecosystem services of pollinator diversity: a review of the relationship with pollen limitation of plant reproduction.Botany-Botanique 90: 535-543 Ecosystem services of pollinator diversity: a review of the relationship with pollen limitation of plant reproduction
ecosystem services; pollination; pollen; insects; flowering plants; pollinator diversity
Recent work on the ecosystem service of biodiversity suggests that higher pollinator diversity could lower pollen limitation, but these two aspects of plant-pollinator communities have only rarely been causally connected. Here we present a review of studies that produced quantitative assessments of both pollinator diversity and evenness as well as pollen limitation of focal plant species. Although pollen limitation is expected to be lower when pollinator diversity is high, our analysis suggests this relationship is weak. The relationship may be obscured when features of the plant species (e. g., average level of specialization) are confounded with features of the plant communities (e. g., habitat). We encourage researchers investigating pollen limitation to consider including measures of diversity of the floral visitors, and their effectiveness. These data would permit a more powerful test of the relationships among these variables and improve our understanding of the critical elements of stable plant-pollinator networks. DOI
41.Elle, E; Elwell, SL; Gielens, GA. (2012) The use of pollination networks in conservation.Botany-Botanique 90: 525-534 The use of pollination networks in conservation
biodiversity loss; climate change; invasive species; mutualistic networks; plant-pollinator interactions; pollinator conservation
Recent concern about declines in pollinating insects highlights the need for better understanding of plant-pollinator interactions. One promising approach at the community scale is network analysis, which allows actual interactions to be assessed, unlike biodiversity surveys, which only identify the potentially interacting organisms. We highlight useful network properties for conservation research and examples of their use in the study of rare species, invasive species, responses of communities to climate change, and habitat loss and restoration. We suggest that nestedness, degree, and interaction strength asymmetry are the most useful network properties for applied research on plant-pollinator interactions, but also highlight practical concerns regarding their measurement. We encourage the adoption of a network approach when an understanding of function within communities, rather than simple community composition, is useful for management. DOI
39. Tunbridge, ND; Sears, C; Elle, E. (2011) Variation in floral morphology and ploidy among populations of Collinsia parviflora and Collinsia grandiflora.Botany-Botanique 89: 19-33 Variation in floral morphology and ploidy among populations of Collinsia parviflora and Collinsia grandiflora
Variation in floral form complicates species identification, and when variation in ploidy also occurs, taxonomic designations are significantly compromised. We studied morphological and ploidy variation in sister species Collinsia parviflora Lindl. (small-flowered form) and Collinsia grandiflora Douglas ex Lindl. (large-flowered form), sampling from California, where the species were previously described as diploids, to British Columbia, where morphologically variable populations were more recently designated tetraploid. We found continuous among-population variation in flower size and shape throughout our sampled range. Ploidy variation, estimated using a combination of chromosome counts and flow cytometry, was not associated with flower size. Diploid populations were rare, and both large-flowered and small-flowered diploids were identified. Tetraploid populations were common, geographically dispersed, and exhibited the full range of flower sizes. A few populations of small-flowered plants were putative hexaploids. When large-and small-flowered forms co-occurred, they were diploid and tetraploid, respectively, suggesting morphological differentiation from selection for reproductive isolation between co-occurring plants of different ploidy. Although diploid C. parviflora (small-flowered) and C. grandiflora (large-flowered) occur, the majority of our sample consisted of morphologically variable tetraploids, suggesting that the use of flower size to delineate species is inappropriate. Further research is needed to ensure a true description of species boundaries in this group. DOI
38. Winn, AA; Elle, E; Kalisz, S; Cheptou, PO; Eckert, CG; Goodwillie, C; Johnston, MO; Moeller, DA; Ree, RH; Sargent, RD; Vallejo-Marin, M. (2011) ANALYSIS OF INBREEDING DEPRESSION IN MIXED-MATING PLANTS PROVIDES EVIDENCE FOR SELECTIVE INTERFERENCE AND STABLE MIXED MATING.Evolution 65: 3339-3359 ANALYSIS OF INBREEDING DEPRESSION IN MIXED-MATING PLANTS PROVIDES EVIDENCE FOR SELECTIVE INTERFERENCE AND STABLE MIXED MATING
Age-specific expression of inbreeding depression; gynodioecy; mating-system evolution; outcrossing; purging; selfing
Hermaphroditic individuals can produce both selfed and outcrossed progeny, termed mixed mating. General theory predicts that mixed-mating populations should evolve quickly toward high rates of selfing, driven by rapid purging of genetic load and loss of inbreeding depression (ID), but the substantial number of mixed-mating species observed in nature calls this prediction into question. Lower average ID reported for selfing than for outcrossing populations is consistent with purging and suggests that mixed-mating taxa in evolutionary transition will have intermediate ID. We compared the magnitude of ID from published estimates for highly selfing (r > 0.8), mixed-mating (0.2 =r= 0.8), and highly outcrossing (r < 0.2) plant populations across 58 species. We found that mixed-mating and outcrossing taxa have equally high average lifetime ID (d= 0.58 and 0.54, respectively) and similar ID at each of four life-cycle stages. These results are not consistent with evolution toward selfing in most mixed-mating taxa. We suggest that prevention of purging by selective interference could explain stable mixed mating in many natural populations. We identify critical gaps in the empirical data on ID and outline key approaches to filling them. DOI
37. Eckert, CG; Kalisz, S; Geber, MA; Sargent, R; Elle, E; Cheptou, PO; Goodwillie, C; Johnston, MO; Kelly, JK; Moeller, DA; Porcher, E; Ree, RH; Vallejo-Marin, M; Winn, AA. (2010) Plant mating systems in a changing world.Trends in Ecology & Evolution 25: 35-43 Plant mating systems in a changing world
There is increasing evidence that human disturbance can negatively impact plant-pollinator interactions such as outcross pollination. We present a meta-analysis of 22 studies involving 27 plant species showing a significant reduction in the proportion of seeds outcrossed in response to anthropogenic habitat modifications. We discuss the evolutionary consequences of disturbance on plant mating systems, and in particular whether reproductive assurance through selfing effectively compensates for reduced outcrossing. The extent to which disturbance reduces pollinator versus mate availability could generate diverse selective forces on reproductive traits. Investigating how anthropogenic change influences plant mating will lead to new opportunities for better understanding of how mating systems evolve, as well as of the ecological and evolutionary consequences of human activities and how to mitigate them. DOI
36.Elle, E; Gillespie, S; Guindre-Parker, S; Parachnowitsch, AL. (2010) VARIATION IN THE TIMING OF AUTONOMOUS SELFING AMONG POPULATIONS THAT DIFFER IN FLOWER SIZE, TIME TO REPRODUCTIVE MATURITY, AND CLIMATE.American Journal of Botany 97: 1894-1902 VARIATION IN THE TIMING OF AUTONOMOUS SELFING AMONG POPULATIONS THAT DIFFER IN FLOWER SIZE, TIME TO REPRODUCTIVE MATURITY, AND CLIMATE
climate; Collinsia parviflora; delayed selfing; flower morphology; phenology; Plantaginaceae; prior selfing
Premise of the study: Early reproductive maturity is common in dry and ephemeral habitats and often associated with smaller flowers with increased potential for within-flower (autonomous) self-pollination. We investigated whether populations from locations that differ in moisture availability, known to vary for whole-plant development rate, also varied in the timing of autonomous selfing. This timing is of interest because the modes of selfing (prior, competing, and delayed) have different fitness consequences. Methods: We measured timing of anther dehiscence, stigma receptivity, and herkogamy under pollinator-free conditions for plants from three populations of Collinsia parviflora that differed in annual precipitation, flower size, and time to sexual maturity. Using a manipulative experiment, we determined potential seed production via prior, competing, and delayed autonomous selfing for each population. Key results: Stigma receptivity, anther dehiscence, and selfing ability covaried with whole-plant development and climate. Plants from the driest site, which reached sexual maturity earliest, had receptive stigmas and dehiscent anthers in bud. Most seeds were produced via prior selfing. The population from the wettest site with slowest development was not receptive until after flowers opened. Although competing selfing was possible, all selfing was delayed. The intermediate population was between these extremes, with significant contributions from both competing and delayed selfing. Conclusions: Our results demonstrate that within-species variation in the timing of selfing occurs and is related to both environmental conditions and whole-plant development rates. We suggest that, if these results can be generalized to other species, mating systems may evolve in response to ongoing climatic change. DOI
35. Goodwillie, C; Sargent, RD; Eckert, CG; Elle, E; Geber, MA; Johnston, MO; Kalisz, S; Moeller, DA; Ree, RH; Vallejo-Marin, M; Winn, AA. (2010) Correlated evolution of mating system and floral display traits in flowering plants and its implications for the distribution of mating system variation.New Phytologist 185: 311-321 Correlated evolution of mating system and floral display traits in flowering plants and its implications for the distribution of mating system variation
LEPTOSIPHON-JEPSONII POLEMONIACEAE; NUMBER TRADE-OFF; SELF-FERTILIZATION; INBREEDING DEPRESSION; RESOURCE-ALLOCATION; FEMALE FUNCTIONS; POLLINATOR VISITATION; PHYLOGENETIC EVIDENCE; FITNESS CONSEQUENCES; INFLORESCENCE SIZE
P> Reduced allocation to structures for pollinator attraction is predicted in selfing species. We explored the association between outcrossing and floral display in a broad sample of angiosperms. We used the demonstrated relationship to test for bias against selfing species in the outcrossing rate distribution, the shape of which has relevance for the stability of mixed mating. Relationships between outcrossing rate, flower size, flower number and floral display, measured as the product of flower size and number, were examined using phylogenetically independent contrasts. The distribution of floral displays among species in the outcrossing rate database was compared with that of a random sample of the same flora. The outcrossing rate was positively associated with the product of flower size and number; individually, components of display were less strongly related to outcrossing. Compared with a random sample, species in the outcrossing rate database showed a deficit of small floral display sizes. We found broad support for reduced allocation to attraction in selfing species. We suggest that covariation between mating systems and total allocation to attraction can explain the deviation from expected trade-offs between flower size and number. Our results suggest a bias against estimating outcrossing rates in the lower half of the distribution, but not specifically against highly selfing species. DOI
34. Mayberry, RJ; Elle, E. (2010) Conservation of a rare plant requires different methods in different habitats: demographic lessons from Actaea elata.Oecologia 164: 1121-1130 Conservation of a rare plant requires different methods in different habitats: demographic lessons from Actaea elata
Elasticity; Endangered species; Finite rate of increase; Population projection; Tall bugbane
Understanding species decline and conserving endangered species requires demographic information, and variation in the environment may affect demography. Actaea elata is a globally rare, perennial herb found in a range of Pacific Northwest forest stand types that differ in canopy openness. Canopy openness increases reproductive output in this species and so was expected to have demographic impact. We performed a demographic analysis of A. elata in contrasting forest stands (broadleaved vs. coniferous) over two annual intervals, and predicted that population growth rate would be higher in the open-canopy broadleaved stand. Population growth was determined using stage-based matrix models, and the most influential transitions were identified using elasticity analyses. The finite rate of population increase (lambda) was lower for the two transition periods at the broadleaved stand than at the coniferous stand (lambda = 0.86 and 0.87 vs. 0.94 and 0.98), even though the former population was more fecund. The decline in the broadleaved stand reflects greater mortality and retrogression to previous stages, partly as a consequence of herbivory. In contrast, lower recruitment occurred in the coniferous stand, but there was also less mortality and retrogression. Our results suggest that management decisions for conservation of A. elata should be tailored to differing habitats, with a focus on preventing mortality in some populations and increasing recruitment in others. DOI
33. Johnston, MO; Porcher, E; Cheptou, PO; Eckert, CG; Elle, E; Geber, MA; Kalisz, S; Kelly, JK; Moeller, DA; Vallejo-Marin, M; Winn, AA. (2009) Correlations among Fertility Components Can Maintain Mixed Mating in Plants.American Naturalist 173: 1-11 Correlations among Fertility Components Can Maintain Mixed Mating in Plants
FLORAL DISPLAY SIZE; SELF-FERTILIZATION; INBREEDING DEPRESSION; REPRODUCTIVE ASSURANCE; DELETERIOUS MUTATIONS; NATURAL-POPULATIONS; OUTCROSSING RATES; SYSTEM EVOLUTION; POLLEN TRANSFER; SELECTION; functional relation; inbreeding depression; pollen discounting; self-fertilization; selective constraint; trade-off
Classical models studying the evolution of self-fertilization in plants conclude that only complete selfing and complete outcrossing are evolutionarily stable. In contrast with this prediction, 42% of seed-plant species are reported to have rates of self-fertilization between 0.2 and 0.8. We propose that many previous models fail to predict intermediate selfing rates because they do not allow for functional relationships among three components of reproductive fitness: self-fertilized ovules, outcrossed ovules, and ovules sired by successful pollen export. Because the optimal design for fertility components may differ, conflicts among the alternative pathways to fitness are possible, and the greatest fertility may be achieved with some self-fertilization. Here we develop and analyze a model to predict optimal selfing rates that includes a range of possible relationships among the three components of reproductive fitness, as well as the effects of evolving inbreeding depression caused by deleterious mutations and of selection on total seed number. We demonstrate that intermediate selfing is optimal for a wide variety of relationships among fitness components and that inbreeding depression is not a good predictor of selfing-rate evolution. Functional relationships subsume the myriad effects of individual plant traits and thus offer a more general and simpler perspective on mating system evolution. DOI
32. Mayberry, RJ; Elle, E. (2009) Effects of forest structure and microhabitat on the distribution and flowering of a rare understory plant, Actaea elata.Forest Ecology and Management 258: 1102-1109 Effects of forest structure and microhabitat on the distribution and flowering of a rare understory plant, Actaea elata
PROJECTION MATRIX ANALYSIS; DOUGLAS-FIR FORESTS; WESTERN WASHINGTON; POPULATION-GROWTH; HEMLOCK FORESTS; PRIMULA-VERIS; HERB; HABITAT; VEGETATION; REGENERATION
Knowing which environmental characteristics constrain forest understory species' distribution and reproduction can inform conservation decisions about habitat management and locations for reintroduction efforts. Differential plant performance is common in varying environmental conditions, such as levels of canopy closure. Actaea elata (tall bugbane) is a rare, perennial, forest understory herb found from Oregon to British Columbia. Populations throughout this species' range commonly occur in managed forests. We assessed the importance of environmental variation on the distribution and flowering of A. elato at both microhabitat and site-level scales. At four sites encompassing a variety of forest types, we measured several biotic and abiotic variables at vegetative and reproductive plants, as well as at random points. We measured these same variables at three sites where A. elata has been extirpated. Within occupied sites, reproductive plants were more likely to be located in canopy gaps than were vegetative plants. Both vegetative and reproductive plants were more likely to be found in areas of high herb cover compared to random points. These results indicate that gaps in the canopy may be critical for this species' ability to reproduce, but survival may be possible in a broader range of forest understory conditions (similar to other co-occurring herb species). Random points at extirpated and occupied sites both tended to be located in areas of lower canopy openness and moisture availability than points in occupied sites where A. elata was present. Extirpated sites were either densely forested or clearcut, while occupied sites contained stands of intermediate density. Circaea alpina, Geranium robertianum, and Lactuca muralis were indicator species for A. elato and normally indicate moist soils, with Circaea alpina being a strong indicator of the presence of flowering A. elata. Taken together, our results suggest that maintenance of canopy gaps is important to promote flowering, and understory species that indicate moist sites, particularly Circaea alpina, can be used as aids to locate new populations of A. elata. (C) 2009 Elsevier B.V. All rights reserved. DOI
30. Cahill, JF; Elle, E; Smith, GR; Shore, BH. (2008) Disruption of a belowground mutualism alters interactions between plants and their floral visitors.Ecology 89: 1791-1801 Disruption of a belowground mutualism alters interactions between plants and their floral visitors
Aspen Parkland; Kinsella; Alberta; Canada; community ecology; grassland; indirect interactions; interactions at multiple trophic levels; mutualisms; mycorrhizae; plant-soil interactions; pollination biology
Plants engage in diverse and intimate interactions with unrelated taxa. For example, aboveground. oral visitors provide pollination services, while belowground arbuscular mycorrhizal fungi (AMF) enhance nutrient capture. Traditionally in ecology, these processes were studied in isolation, reinforcing the prevailing assumption that these above- and belowground processes were also functionally distinct. More recently, there has been a growing realization that the soil surface is not a barrier to many ecological interactions, particularly those involving plants (who live simultaneously above and below ground). Because of the potentially large impact that mycorrhizae and. oral visitors can have on plant performance and community dynamics, we designed an experiment to test whether these multi-species mutualisms were interdependent under field conditions. Using benomyl, a widely used fungicide, we suppressed AMF in a native grassland, measuring plant, fungal, and floral-visitor responses after three years of fungal suppression. AMF suppression caused a shift in the community of. oral visitors from large-bodied bees to small-bodied bees and flies, and reduced the total number of. oral visits per flowering stem 67% across the 23 flowering species found in the plots. Fungal suppression has species-specific effects on. oral visits for the six most common flowering plants in this experiment. Exploratory analyses suggest these results were due to changes in. oral-visitor behavior due to altered patch-level. oral display, rather than through direct effects of AMF suppression on. oral morphology. Our findings indicate that AMF are an important, and overlooked, driver of. oral-visitor community structure with the potential to affect pollination services. These results support the growing body of research indicating that interactions among ecological interactions can be of meaningful effect size under natural field conditions and may influence individual performance, population dynamics, and community structure. DOI
29. Kennedy, BF; Elle, E. (2008) The reproductive assurance benefit of selfing: importance of flower size and population size.Oecologia 155: 469-477 The reproductive assurance benefit of selfing: importance of flower size and population size
autonomous selfing; Collinsia parviflora; habitat fragmentation; pollen limitation; reproductive assurance
Autonomous selfing can provide reproductive assurance (RA) for flowering plants that are unattractive to pollinators or in environments that are pollen limited. Pollen limitation may result from the breakdown of once-continuous habitat into smaller, more isolated patches (habitat fragmentation) if fragmentation negatively impacts pollinator populations. Here we quantify the levels of pollen limitation and RA among large and small populations of Collinsia parviflora, a wildflower with inter-population variation in flower size. We found that none of the populations were pollen limited, as pollen-supplemented and intact flowers did not differ in seed production. There was a significant effect of flower size on RA; intact flowers (can self) produced significantly more seeds than emasculated flowers (require pollen delivery) in small-flowered plants but not large-flowered plants. Population size nested within flower size did not significantly affect RA, but there was a large difference between our two replicate populations for large-flowered, small populations and small-flowered, large populations that appears related to a more variable pollination environment under these conditions. In fact, levels of RA were strongly negatively correlated with rates of pollinator visitation, whereby infrequent visitation by pollinators yielded high levels of RA via autonomous selfing, but there was no benefit of autonomous selfing when visitation rates were high. These results suggest that autonomous selfing may be adaptive in fragmented habitats or other ecological circumstances that affect pollinator visitation rates. DOI
28. Kennedy, BF; Elle, E. (2008) THE INBREEDING DEPRESSION COST OF SELFING: IMPORTANCE OF FLOWER SIZE AND POPULATION SIZE IN COLLINSIA PARVIFLORA (VERONICACEAE).American Journal of Botany 95: 1596-1605 THE INBREEDING DEPRESSION COST OF SELFING: IMPORTANCE OF FLOWER SIZE AND POPULATION SIZE IN COLLINSIA PARVIFLORA (VERONICACEAE)
Collinsia parviflora; floral morphology; habitat fragmentation; inbreeding depression; mating system evolution; Veronicaceae; Vancouver Island
Inbreeding depression should evolve with selting rate when frequent inbreeding results in exposure of and selection against deleterious alleles. The selting rate may be modified by plant traits such as flower size. or by population characteristics such as census size that can affect the probability of biparental inbreeding. Here we quantify inbreeding depression(delta) among different populatio sizes of Collinsia parviflora, a wildflower with interpopulation variation in flower size, by comparing fitness components and multiplicative fitness of experimentally produced selfed and outcrossed offspring. Selfed offspring had reduced multiplicative fitness compared to outcrossed offspring but inbreeding depression was low in all combinations of population size and flower size (delta <= 0.05) except in large populations of large-flowered plant (delta=0.45). The decrement to multiplicative fitness with inbreeding was not affected by population size nested within flower size but differed between small- and large-flowered plants: small-flowered populations had lower overall inbreeding depression (delta=0.45). The decrement to multiplicative fitness with inbreeding was not affected by population size nested within flower size, but differed between small- and large-flowered plants: small-flowered populations had lower overall inbreeding depression (delta=0.04) compared to large-flowered population (delta=0.25). The difference in load with flower size suggests that either selection has removed deleterious recessive alleles or these alleles have become fixed in small-flowered, potentially more selfing population, but that purging has not occured to the same extent in presumably outcrossing large-flowered populations. DOI
27. Biernaskie, JM; Elle, E. (2007) A theory for exaggerated secondary sexual traits in animal-pollinated plants.Evolutionary Ecology 21: 459-472 A theory for exaggerated secondary sexual traits in animal-pollinated plants
asymmetric competition; bout length; ESS; floral display size; mean fitness; nectar production rate; plant's dilemma; pollinator attraction; sex allocation; sexual selection
We analyze two mathematical models of adaptive investment in rewarding plant traits. In both models, the attractiveness of a particular trait value declines as the mean value in the population increases (asymmetric competition), giving relatively rewarding traits a competitive advantage. Including this competition for pollinator visits in a standard model of hermaphroditic sex allocation shifts additional allocation to pollinator rewards at the expense of allocation to pollen and seeds. In the second model, plants can invest additional resources in pollinator rewards but suffer reduced viability and rising costs due to excess pollen removal and within-plant selfing (geitonogamy). Despite these accumulating costs, increasing the magnitude of asymmetric competition exaggerates the ESS investment in rewards beyond the equilibrium in cases where attractiveness depends only on a plant's absolute reward value. We suggest that the type of frequency dependent selection modeled here is fundamentally equivalent to sexual selection in animal populations (with some unique exceptions). Testing the main assumptions of our models may reveal whether seemingly "extravagant" floral traits are strictly analogous to the exaggerated secondary sexual traits of animals. DOI
26. Cahill, James F., Jr.; Smith, Glen R.; Shore, Bryon H.; Elle, Elizabeth. (2007) Disruption of a belowground mutualism alters plant-pollinator interactions.Ecological Society of America Annual Meeting Abstracts San Jose, CA, USA August 05 -10, 2007 Disruption of a belowground mutualism alters plant-pollinator interactions
24. Vamosi, JC, SL Goring, BF Kennedy, RJ Mayberry, CM Moray, LA Neame, ND Tunbridge, E. and E Elle. (2007) Pollination, floral display, and the ecological correlates of polyploidy.Functional Ecosystems and Communities 1: 1-9. (Invited Review) Pollination, floral display, and the ecological correlates of polyploidy.
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23. Biernaskie, JM; Elle, E. (2005) Conditional strategies in an animal-pollinated plant: size-dependent adjustment of gender and rewards.Evolutionary Ecology Research 7: 901-913 Conditional strategies in an animal-pollinated plant: size-dependent adjustment of gender and rewards
bumblebees; Chamerion; Epilobium; inflorescence design; nectar gradient; nectar production rate; patch departure; pollen dispensing; sex allocation
Question: How do hermaphroditic flowering plants that must attract animal pollinators allocate to flower production, seed production and nectar production among flowers, as functions of their individual size and the size of their floral display? Organism: Chamerion (= Epilobium) angustifolium; vertical inflorescences display male-phase flowers above female-phase flowers. Site: Silver Star Mountain, Vernon, British Columbia, Canada. Methods: We measured nectar production from male- and female-phase flowers across a range of display sizes. By experiment, we determined the effect of alternative nectar distributions on bumblebee foraging. We measured total flower production (male investment), seed production (female investment) and plant size. Results: Large floral displays allocated extra nectar production to female-phase flowers. Bumblebees probed fewer male-phase flowers per visit when extra nectar was added to female-phase flowers than when nectar was added more evenly among gender phases. Large plants produced about a third fewer flowers per gram of plant biomass than did the smallest plants. But large plants matured a nearly proportional number of seeds.
22. Parachnowitsch, AL; Elle, E. (2005) Insect visitation to wildflowers in the endangered Garry Oak, Quercus garryana, ecosystem of British Columbia.Canadian Field-Naturalist 119: 245-253 Insect visitation to wildflowers in the endangered Garry Oak, Quercus garryana, ecosystem of British Columbia
Garry Oak ecosystem; Quercus garryana plant-pollinator interactions; Common Camas; Camassia quamash; British Columbia
The Garry Oak Ecosystem (GOE) is a fragmented and endangered ecosystem in Canada, and is currently the focus of conservation and restoration efforts in British Columbia. However, little is known about the basic biology of GOE forbs, or their relationships with pollinating insects. We monitored wildflowers and their insect visitors in 25 quadrats within a 25 x 25 metre plot, located in a fragment of the GOE near Duncan, British Columbia, for six weeks (the majority of the flowering period). Overall, 21 native and non-native forb species flowered in our quadrats during the survey, and we observed an additional six forb species flowering outside of our quadrats. Eight forbs were visited within quadrats by a total of 13 insect taxa, identified to morphospecies. Visits by eight additional morphospecies were observed outside of the quadrats. In general, visitation was low; however, most insect morphospecies were observed visiting more than one plant species, and most plant species were visited by more than one insect morphospecies, suggesting that pollination may be generalised in this community. A chi(2) analysis indicated that insect visitation was not proportional to the relative abundance of forbs, with higher than expected visitation to Common camas (Camassia quamash), and no observed visits to 11 species, most with very small (putatively unattractive) flowers. The most frequent insect visitor was the introduced Honeybee, Apis mellifera, followed by native mason bees (Osmia spp.) and mining bees (Andrena spp.). Our observations provide baseline data for future, detailed studies that should investigate the importance of plant-pollinator mutualisms for sustainability of populations and communities in this rare ecosystem.Website
21. Stastny, M; Schaffner, U; Elle, E. (2005) Do vigour of introduced populations and escape from specialist herbivores contribute to invasiveness?Journal of Ecology 93: 27-37 Do vigour of introduced populations and escape from specialist herbivores contribute to invasiveness?
enemy release hypothesis (ERH); evolution of increased competitive ability (EICA); herbivore resistance; herbivore tolerance; invasive species; Longitarsus jacobaeae; Senecio jacobaea; vigour
1 Plant species may become invasive due to a lack of natural enemies (e.g. herbivores) in their introduced range. Absence of herbivores may result in selection for the loss of costly herbivore-resistance traits, which are expected to show a trade-off with vigour or competitive ability (the evolution of increased competitive ability, or EICA, hypothesis). 2 We conducted a common garden experiment in Switzerland, in which we compared herbivore resistance and vigour of Senecio jacobaea plants exposed to the specialist flea beetle Longitarsus jacobaeae, for four populations originating within the native range (Europe), and four from regions where it had been introduced (New Zealand, USA) and was unaffected by L. jacobaeae. Our predictions were that, compared with plants from the native populations, plants from introduced populations would experience greater herbivory (due to loss of resistance traits), and exhibit more vigorous growth. 3 As expected, we found that introduced S. jacobaea grew larger, and had greater reproductive output, than plants from the native range. Larger plants experienced more feeding damage, and introduced plants were consumed more even when size differences were controlled. Introduced plants also exhibited a greater relative ability to reproduce after damage was sustained, i.e. higher tolerance to herbivory. 4 Contrary to predictions, however, plants from introduced populations had higher total pyrrolizidine alkaloid production (chemical defence against herbivores). 5 Although plants from introduced ranges exhibited life-history traits consistent with EICA predictions, similar phenotypes were common in one of the populations from the native range, suggesting that EICA may not fully explain the invasion success of S. jacobaea. 6 Our results imply that increased competitive ability (vigour) of invasive plants may be associated with changes in resistance as well as tolerance to herbivory, and both types of anti-herbivore defence may need to be examined simultaneously to advance our understanding of invasiveness. DOI
20.Elle, E. (2004) Floral adaptations and biotic and abiotic selection pressures.Plant Adaptation: Molecular Genetics and Ecology 111-118 (Conference 2002 UBC Bot Garden & Ctr Plant Res, Vancouver, CANADA) Floral adaptations and biotic and abiotic selection pressures
Explanations for the evolution of floral phenotypes have historically focussed on pollinator choice, but phenotypes also reflect adaptation to abiotic selection pressures. Populations of Collinsia parvifloro vary significantly in floral phenotype, specifically in corolla size. Traditional explanations for this variation (pollinator choice and the reproductive assurance benefit of selfing) explain some of the phenotypic variation observed. However, genetic correlations between corolla size and time to reproductive maturity indicate that an abiotic factor, pattern of precipitation, may also be an important agent of selection. Rapidly developing populations of C. parviflora have small flowers and are found in drier, more ephemeral, ecological settings, where there is limited time to grow large and build large flowers. There has been extensive research on the molecular switch to flowering in model genetic systems; this research on a native plant species suggests that studying natural variation in developmental traits may be a productive way to link molecular genetic and ecological approaches to research on plant adaptation.
19. Hare, JD; Elle, E. (2004) Survival and seed production of sticky and velvety Datura wrightii in the field: A five-year study.Ecology 85: 615-622 Survival and seed production of sticky and velvety Datura wrightii in the field: A five-year study
costs of resistance; Datura wrightii; demographic analysis; geographic variation; resistance polymorphism; trichomes
Leaves of Datura wrightii in California (USA) are covered either with glandular trichomes ("sticky" plants) or non-glandular trichomes ("velvety" plants), and sticky plants are resistant to many insect herbivores. Theoretical models suggest that variation in resistance to herbivores may persist if resistance is costly and herbivore damage is variable. If so, then natural selection should favor resistant plants when damage is high and disfavor it when damage is low. However, without long-term equivalence between costs and benefits, then natural selection either should drive the trait to fixation if it has a net benefit or eliminate it if it has a net cost. Previously we showed that the production of glandular trichomes carried a net cost in short-term studies, suggesting that this expensive resistant trait might be eliminated from D. wrightii populations. To test this hypothesis we monitored survival and seed production of sticky and velvety D. wrightii in the presence of herbivores in 11 natural populations over four or five years. In eight populations where both types occurred, the finite rate of increase for velvety plants was 60-274% greater than for sticky plants. Plant survival averaged between two and three years and did not differ significantly between types. Because seed production consistently favored velvety plants, our prediction that the proportion of sticky plants should decline was met within five years in seven of those eight populations. If the variation in trichome morphology in D. wrightii is indeed maintained by variation in costs and benefits of glandular trichomes, then the periodicity of such variation extends over more than five seasons. DOI
18. Parachnowitsch, AL; Elle, E. (2004) Variation in sex allocation and male-female trade-offs in six populations of Collinsia parviflora (Scrophulariaceae s.l.).American Journal of Botany 91: 1200-1207 Variation in sex allocation and male-female trade-offs in six populations of Collinsia parviflora (Scrophulariaceae s.l.)
Collinsia parviflora; flower size; mating system; pollen; ovule ratios; pollen size; Scrophulariaceae; sex allocation; trade-off
Assumed trade-offs between male and female functions in hermaphroditic flowers have been difficult to demonstrate. Collinsia parviflora (Scrophulariaceae) is a winter annual that exhibits significant among-population variation in corolla size in British Columbia, Canada. We asked whether reduction in secondary male allocation (i.e., the attractive corolla), a preliminary indicator of mating system, was matched by a reduction in primary male allocation (i.e., pollen production), and whether there were allocation trade-offs between male and female function both within and among six study populations. Larger-flowered populations allocated more to male function (androecium and corolla biomass), and because populations did not vary in female biomass allocation (gynoecium and calyx), population differences were not due to simple allometric scaling. Populations also differed in per-flower gamete production (pollen and ovules). We found male-female trade-offs within populations between androecium and gynoecium mass and between corolla and calyx mass. Among populations, there was a marginal trade-off between pollen and ovule production and a significant within-male trade-off between pollen grain size and number. Trade-offs between the sexes were primarily apparent when we controlled for flower size in the analysis. Variation among populations in sex allocation may reflect different optima related to the mating system. DOI
17. Sabara, HA; Gillespie, DR; Elle, E; Winston, ML. (2004) Influence of brood, vent screening, and time of year on honey bee (Hymenoptera : Apidae) pollination and fruit quality of greenhouse tomatoes.Journal of Economic Entomology 97: 727-734 Influence of brood, vent screening, and time of year on honey bee (Hymenoptera : Apidae) pollination and fruit quality of greenhouse tomatoes
honey bee; Apis mellifera; pollination; greenhouse; tomatoes
Greenhouse tomatoes, Lycopersicon esculentum Miller (Solanaceae), are autogamous, but facilitated pollination results in increased fruit size and set. Previous research examining honey bee pollination in greenhouse tomato crops established that fruit quality resulting from honey bee visitation is often comparable to humble bees (Bombus spp.) and significantly better than in flowers that receive no facilitated pollination. However, management alternatives have not been studied to improve tomato fruit quality when honey bees are the only pollination option available for the high-value greenhouse industry. We investigated whether the quantity of brood (eggs, larvae, and pupae) in a honey bee colony in the winter and screening on greenhouse vents in the summer would encourage honey bee foraging on tomato flowers. We also established the influence of time of year on the potential for honey bees to be effective pollinating agents. We constructed small honey bee colonies full of naive forager bees with either two frames of brood ("brood colonies") or two empty frames ("no-brood") and compared total fruit set and the number of tomato seeds resulting from fruit potentially visited by honey bees in each of these treatments to bagged flowers that received no facilitated pollination. There was no significant difference in the quality of fruit resulting from honey bees from "brood" and "no-brood" colonies. However, these fruits produced significantly more seeds than bagged flowers restricted from facilitated pollination. Honey bees from brood and no-brood colonies also resulted in 98% fruit set compared with 80% fruit set in bagged flowers that received no facilitated pollination. During the summer, the number of seeds per fruit did not differ significantly between unbagged flowers potentially visited by honey bees in screened greenhouses and unscreened greenhouses and bagged flowers that received no facilitated pollination. However, time of year did have a significant influence on the quality of fruit produced by honey bees compared with flowers that received no facilitated pollination, because no difference in seed number was observed between the treatments after mid-April. The results from this study demonstrate that the management of brood levels and vent screening cannot be used to improve the quality of fruit resulting from honey bee pollination and that honey bees can be a feasible greenhouse pollination alternative only during the winter. DOI
16.Elle, E; Carney, R. (2003) Reproductive assurance varies with flower size in Collinsia parviflora (Scrophulariaceae).American Journal of Botany 90: 888-896 Reproductive assurance varies with flower size in Collinsia parviflora (Scrophulariaceae)
autogamy; Collinsia parviflora; floral morphology; plant mating systems; pollinator limitation; reproductive assurance; Scrophulariaceae; Vancouver Island
A central question in plant evolutionary ecology is how mixed mating systems are maintained in the face of selection against self-pollination. Recently, attention has focused on the potential reproductive assurance (RA) benefit of selling: the ability to produce seeds via autonomous selfing when the potential for outcrossing is reduced or absent. To date, there is little experimental support for this benefit under natural pollination conditions. In addition, the RA hypothesis has not been tested experimentally in a species displaying morphological variation for traits expected to influence the mating system, such as flower size, which affects both attractiveness to pollinators and ability to self autonomously. Here, we document significant among-population variation in flower size in Collinsia parviflora and show that pollinators preferred large flowers over small flowers in experimental arrays. The pollinator community varied among three study sites, and two small-flowered populations had lower pollinator visitation rates than one large-flowered population. We compared seed production between intact flowers (can self) and experimentally emasculated flowers (require a pollinator) on large- and small-flowered plants. As predicted by the RA hypothesis, small-flowered plants show a greater RA benefit of selling than large-flowered plants; emasculated, small flowers produced very few seeds, relative to intact, small flowers or either emasculated or intact, large flowers. We also show that the RA benefit is pollination-context dependent, differing between small- and large-flowered test sites, likely due to a combination of pollinator discrimination against small flowers and differences between test sites in the pollinator community. This paper is the first experimental evidence showing a trait-dependent RA benefit of selfing under natural pollination conditions. DOI
14. Hare, JD; Elle, E; van Dam, NM. (2003) Costs of glandular trichomes in Datura wrightii: A three-year study.Evolution 57: 793-805 Costs of glandular trichomes in Datura wrightii: A three-year study
allocation trade-offs; cost of resistance; Datura wrightii; demographic analysis; herbivory; resistance polymorphism; trichomes
Models accounting for genetic variation for resistance to herbivores within plant populations often postulate a balance between the costs of that resistance and its benefits. The production of glandular trichomes by Datura wrightii was shown to be costly in a previous one-year study because plants producing glandular trichomes (sticky plants), a factor conferring resistance to some insect herbivores, also produced 45% fewer seeds than plants producing nonglandular trichomes (velvety plants) when grown in a common garden. Because sticky plants tended to be larger than velvety plants but produced fewer seed capsules, we postulated an allocation trade-off in which velvety plants are more reproduction-dominated whereas sticky plants are more growth-dominated. If a greater commitment to vegetative growth eventually allows sticky plants to compensate for reduced seed production, we would expect a reduction or elimination of the cost of resistance over time in this perennial plant. We monitored growth, survival, and seed production of plants from defined crosses of local populations for three years in a common garden when exposed to and protected from herbivores, and with and without supplemental water. The majority of plants exposed to herbivores had died by the end of the study. We used standard life-table methods to determine the net reproductive rate (R-0) and the finite rate of increase (lambda) of plants of each trichome type. After three years, when plants were protected from herbivores, sticky plants were 187-245% larger than velvety plants, depending upon irrigation treatment, but sticky plants continued to be less efficient in producing seeds per unit of canopy volume. Even though the total seed production of sticky plants eventually equaled that of velvety plants, the advantage of earlier reproduction by velvety plants increased lambda by 55-230% over that of sticky plants, depending upon herbivore and irrigation treatment. Exposure to herbivores reduced lambda by 69-83%, depending upon plant type and irrigation treatment, whereas supplemental irrigation increased lambda by 29-175%, depending upon plant type and exposure to herbivores. Although there was a large allocation trade-off between growth and reproduction, the benefits of such a trade-off did not emerge before most plants were killed by herbivores. The cost of producing glandular trichomes strictly for herbivore resistance continued to exceed its benefits, and in the absence of other, unmeasured benefits from the suite of life-history characters associated with glandular trichome production, natural selection is expected to eliminate this costly resistance trait from D. wrightii populations. DOI
13.Elle, E; Hare, JD. (2002) Environmentally induced variation in floral traits affects the mating system in Datura wrightii.Functional Ecology 16: 79-88 Environmentally induced variation in floral traits affects the mating system in Datura wrightii
floral display; herbivory; herkogamy; outcrossing rate; self pollination; water availability
1. If pollination is unpredictable, selection may favour the production of selfed seeds in the absence of pollen vectors, even in plant species with obvious adaptations for outcrossing. Pollination may be less predictable for plants growing in certain environments if environmental factors affect the floral phenotype. Through effects on flower morphology and the floral display, the environment may affect the outcrossing rate. 2. We manipulated two environmental factors, water availability and exposure to insect herbivores, in a common-garden experiment using a perennial herb, Datura wrightii. We measured herkogamy (the separation of anthers and stigmas within flowers), total flower length, and flower number, and used a single-gene trichome dimorphism as a marker to determine per-plant outcrossing rates. 3. The large amount of variation in herkogamy was affected by trichome type, irrigation and herbivory. In addition, watered plants had longer corollas, and plants attacked by herbivores had fewer open flowers. Thus environmental factors affect floral phenotype. 4. However, irrigation and herbivory did not directly affect outcrossing rate. There were indirect effects of these treatments on outcrossing because plants with increased herkogamy and fewer open flowers had higher outcrossing rates. 5. A greenhouse experiment showed that autonomous selfing is more likely when herkogamy is reduced, and can occur both as the flower opens and when the corolla is shed. 6. These experiments are among the first to show that within-population variation in the mating system can be due to environmentally induced variation in floral traits. DOI
11. Hare, JD; Elle, E. (2002) Variable impact of diverse insect herbivores on dimorphic Datura wrightii.Ecology 83: 2711-2720 Variable impact of diverse insect herbivores on dimorphic Datura wrightii
Datura wrightii; ecological cost; herbivore community; plant defense; plant fitness; trichomes; Tupiocoris notatus; water availability
Traits that confer plant resistance to some herbivore species but increase plant susceptibility to other herbivore species are said to carry an "ecological cost" of herbivore resistance. The native perennial, Datura wrightii, is dimorphic for leaf trichome type, and the production of glandular trichomes carries a potential ecological cost over the production of nonglandular trichomes. Glandular trichomes provide resistance to at least six herbivore species, but they also confer susceptibility to Tupiocoris notatus, an abundant mirid bug with special adaptations to glandular trichomes. We estimated herbivore-specific damage to plants of each trichome type and measured plant seed production, a component of fitness, in a common garden over three years. Plant seed production increased with the size and persistence of leaf canopies and occasionally declined with increasing damage caused by some of the defoliating insects. Plant seed production was never reduced by T. notatus damage, however. Even though the ecological cost of glandular trichome production was not apparent in D. wrightii, the trait still was not beneficial. The fitness of plants with glandular trichomes never exceeded that of plants with nonglandular trichomes despite variation in both the composition of the herbivore community and the total level of damage inflicted by herbivores over three years of study. The persistence of the allele coding for, glandular trichomes cannot be explained solely on the basis of the herbivore resistance that those trichomes provide. DOI
10. Hare, JD; Elle, E. (2001) Geographic variation in the frequencies of trichome phenotypes of Datura wrightii and correlation with annual water deficit.Madrono 48: 33-37 Geographic variation in the frequencies of trichome phenotypes of Datura wrightii and correlation with annual water deficit
1
The perennial plant species, Datura wrightii Regel (Solanaceae) is dimorphic for leaf trichome type. Some plants produce almost exclusively short, non-glandular trichomes, while other plants within the same population produce almost exclusively longer, glandular trichomes. In a previous survey of 19 southern California populations, the frequency of plants producing glandular trichomes ranged from 0-82%, and plants with glandular trichomes were absent from desert populations. Here we expand our studies to a total of 56 D. wrightii populations from central and southern California. We also examined the relationship between the frequency of glandular trichomes and two factors that broadly determine the availability of water at each site. The first was mean annual rainfall, while the second was mean annual evapotranspiration rate. The frequency of plants with glandular trichomes increased with increasing mean rainfall and decreased with increasing mean annual evapotranspiration rate. Combined, these two environmental variables accounted for about one-third of the variation in the proportion of plants with glandular trichomes. Results suggest that the production of a water-based exudate by plants with glandular trichomes may impose an additional demand for water on those plants compared to plants with non-glandular trichomes. Because of this additional water demand, the frequency of plants with glandular trichomes may decline relative to that of plants with non-glandular trichomes as available water becomes more limiting.
9.Elle, E; Hare, JD. (2000) No benefit of glandular trichome production in natural populations of Datura wrightii?Oecologia 123: 57-65 No benefit of glandular trichome production in natural populations of Datura wrightii?
cost of resistance; Datura wrightii; geographic variation; herbivory; trichomes
Populations of Datura wrightii vary in the frequency of plants that produce glandular trichomes, a resistance trait under the control of a single gene. Such variation may be maintained if the production of glandular trichomes is costly in the absence of herbivory, and if selection imposed by herbivore communities varies spatially or temporally. Here, we document costs in the presence of herbivory for established glandular plants relative to established non-glandular plants growing in natural populations from coastal mountain, Riversidian sage scrub, and Mojave desert habitats in southern California. Damage caused by the herbivore community varied spatially, with significant differences in herbivore-specific damage between plants of the two trichome types and among populations within habitats, although not generally among habitats. Plants with greater canopy size and canopy persistence had higher viable seed production than smaller or more damaged plants, but this relationship was statistically significant only for non-glandular plants. However, the relationship between viable seed production and canopy persistence became significant for glandular plants when damage caused by sap suckers, which do not remove leaf area, was pooled with undamaged leaf area. The high cost exhibited by glandular plants leads us to predict that in the absence of any additional, unknown benefits of producing glandular trichomes, the frequency of these plants should decline in all natural populations of D. wrightii. DOI
8.Elle, E; Meagher, TR. (2000) Sex allocation and reproductive success in the andromonoecious perennial Solanum carolinense (Solanaceae). II. Paternity and functional gender.American Naturalist 156: 622-636 Sex allocation and reproductive success in the andromonoecious perennial Solanum carolinense (Solanaceae). II. Paternity and functional gender
andromonoecy; Bateman's principle; functional gender; paternity analysis; sex allocation; Solanum carolinense
According to Bateman's principle, male fitness in entomophilous plant species should be limited by mating opportunity, which is influenced by the size or number of flowers. We determined male-specific fitness consequences of floral phenotype in andromonoecious Solanum carolinense, examined the relationship between male and female reproductive success within plants, and evaluated the distribution of functional gender among plants. A maximum likelihood-based paternity analysis, based on multilocus allozyme phenotypes of parents and offspring from four experimental plots, was used to determine male reproductive success and its relationship to floral phenotype. Male success was enhanced by an increase in the proportion of male flowers produced but not by an increase in total flower number, even though all flowers contain male parts. Larger flower size increased male success in only one plot. Male and female reproductive success were negatively correlated, and plants varied in functional gender from completely female to completely male. This gender specialization may occur because hermaphroditic and male flowers differ in their ability to contribute to male and female success. Although sex allocation theory predicts a positive relationship between the size or number of plant parts and reproductive success, this study indicates that aspects of floral morphology that affect gender specialization should also be considered. DOI
7.Elle, E. (1999) Sex allocation and reproductive success in the andromonoecious perennial Solanum carolinense (Solanaceae). I. Female success.American Journal of Botany 86: 278-286 Sex allocation and reproductive success in the andromonoecious perennial Solanum carolinense (Solanaceae). I. Female success
Bateman's principle; reproductive success; resource allocation; sex allocation; Solanaceae; Solanum carolinense
Relative allocation of resources to growth vs, reproduction has long been known to be an important determinant of reproductive success. The importance of variation in allocation to different structures within reproductive allocation is somewhat less clear. This study was designed to elucidate the importance of allocation to vegetative vs. reproductive functions, and allocation within reproductive functions (sex allocation), to realized female success in an andromonoecious plant, Solanum carolinense. Allocation measurements were taken on plants in experimental allays exposed to natural pollination conditions. These measurements included total flower number; the proportion of flowers that were male. Bower size. and vegetative size. Flower number explained the majority of the variation among individuals in their success-that is, there was strong selection for increased Bower production. There was also selection to decrease the proportion of flowers that were male, but neither flower size nor vegetative size (a measure of overall resource availability) were direct determinants of female success. After Bonferroni corrections for multiple comparisons. most phenotypic correlations among the traits measured were nonsignificant. Thus, in this andromonoecious species there is not a strong relationship between resource availability (vegetative size) and female success, and female success is instead determined by the relative production of the two different flower types. DOI
6.Elle, E; van Dam, NM; Hare, JD. (1999) Cost of glandular trichomes, a "resistance" character in Datura wrightii Regel (Solanaceae).Evolution 53: 22-35 Cost of glandular trichomes, a "resistance" character in Datura wrightii Regel (Solanaceae)
cost of resistance; Datura wrightii; herbivory; polymorphism; selection; trichomes
Models regarding the evolution of plant resistance to herbivory often assume that the primary mechanism maintaining resistance polymorphisms is the balance between benefits of increased resistance to herbivores and costs associated with the production of a resistance character. However, rarely has it been demonstrated that genetically based resistance traits are costly. Here, we document costs associated with the production of glandular trichomes, a resistance character in Datura wrightii that is predominantly under the control of a single gene of large effect. In the absence of herbivores, plants with glandular trichomes (sticky) produced 45% fewer viable seeds than plants with nonglandular trichomes (velvety). Although both plant types flowered with similar frequency, sticky plants matured fewer capsules and fewer of their seeds germinated. The fitness difference between the types in herbivore-free conditions was not mitigated by the addition of water, a potentially limiting resource for sticky plants. Under herbivore pressure, there was no significant fitness difference between the types, although the fitness of velvety plants was still higher than that of sticky plants. This occurred even though velvety plants sustained more herbivore damage than sticky plants and were more likely to be attacked by most herbivore species present. The fitness difference between the plant types was especially reduced when herbivore-attacked plants were watered, which indicates that sticky plants may have higher tolerance for damage than velvety plants when supplied with a potentially limiting resource. Yet, the maintenance of a fitness deficit (albeit small and nonsignificant) for sticky plants when attacked by herbivores indicates no net benefit associated with the production of glandular trichomes in this first year of our study. These results add to our current understanding that herbivore resistance characters can be costly and raise the question of how this genetic polymorphism is maintained in wild populations. DOI
5. van Dam, NM; Hare, JD; Elle, E. (1999) Inheritance and distribution of trichome phenotypes in Datura wrightii.Journal of Heredity 90: 220-227 Inheritance and distribution of trichome phenotypes in Datura wrightii
Glandular trichomes in plants often confer resistance to herbivorous insects. The native plant species Datura wrightii (Solanaceae) Is polymorphic with regard to trichome morphology, Some mature plants are covered primarily with nonglandular trichomes, while others possess glandular trichomes that excrete a sticky exudate, Both phenotypes were found in nearly all southern California plant populations surveyed, The frequencies of glandular (sticky) and nonglandular (velvety) phenotypes, however, varied significantly among populations. By employing reciprocal hybridization and backcross designs, we showed that trichome phenotype is inherited largely in a Mendelian fashion. The allele coding for the sticky phenotype was dominant over that for the velvety phenotype, The expression of the recessive gene was age dependent; velvety phenotypes produced glandular trichomes on their cotyledons and the first five true leaves. Thereafter these plants produced nonglandular trichomes on all newer leaves, We hypothesize that feeding by herbivorous insects and/or water stress may play a role in maintaining this polymorphism in natural plant populations. DOI
4.Elle, E. (1998) The quantitative genetics of sex allocation in the andromonoecious perennial, Solanum carolinense (L.).Heredity 80: 481-488 The quantitative genetics of sex allocation in the andromonoecious perennial, Solanum carolinense (L.)
breeding systems; genetic correlations; heritability; restricted maximum likelihood; sex allocation; Solanum carolinense
The quantitative genetics of allocation to sexual functions was examined in the andromonoecious plant, Solanum carolinense. A restricted maximum likelihood (REML) analysis was employed to determine heritabilities and genetic and environmental correlations for flower number, the proportion of those flowers that were male, and the size of flower parts (corolla diameter, pistil length, and anther length and width) in each of three populations used in a diallel crossing design. All floral characters were highly heritable. The sizes of flower parts were positively genetically correlated with one another, which will restrict the independent evolution of these parts. Negative genetic and environmental correlations exist between flower size and proportion male flowers, indicating the potential for the evolution of individuals with either many, small male flowers or few, large, cosexual flowers. The high heritabilities of the traits examined as well as the genetic correlations among them indicate the potential for the evolution of gender specialization in this species, because flower size and number have the potential to affect sex-specific reproductive success. DOI
2.Elle, E. (1996) Reproductive trade-offs in genetically distinct clones of Vaccinium macrocarpon, the American cranberry.Oecologia 107: 61-70 Reproductive trade-offs in genetically distinct clones of Vaccinium macrocarpon, the American cranberry
allocation strategy; genetic effects; plant reproduction; trade-offs; Vaccinium macrocarpon
Patterns of resource allocation to growth, current reproduction, and potential future reproduction were quantified in six genetically distinct cultivars of Vaccinium macrocarpon. For all cultivars (genotypes), vegetative size is positively correlated with some measures of current reproduction (fruit and flower number) but negatively correlated with others (seed number per fruit, seed weight per fruit). Vegetative growth in the current year is significantly related to the production of reproductive terminal buds, a measure of the potential for reproduction in the following year. Stems with low levels of current reproduction - lower flower number, fruit number, and seed weight - were more likely to form reproductive terminal buds than stems with higher levels of current reproduction. Individual genotypes differed significantly for vegetative size, fruit number, fruit weight, seed number, and seed weight, as well as for the frequency of fruiting stems and reproductive terminal buds produced. Genotypes were segregated in principal component space, indicating overall differences between them in allocation to the suite of variables measured. These results indicate the possibility of fitness differences among cultivars due to genetically determined allocation strategy, which has implications for fitness differences among genotypes within natural populations. DOI
