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1. Spatial variation in bidirectional pollinator-mediated interactions between two co-flowering species in serpentine plant communities

   https://doi.org/10.1093/aobpla/plab069  

   Stanley, Amber ; Martel, Carlos ; Arceo-Gómez, Gerardo ( December 2021 , AoB PLANTS)

   Boege, Karina (Ed.)

   Abstract Pollinator-mediated competition and facilitation are two important mechanisms mediating co-flowering community assembly. Experimental studies, however, have mostly focused on evaluating outcomes for a single interacting partner at a single location. Studies that evaluate spatial variation in the bidirectional effects between co-flowering species are necessary if we aim to advance our understanding of the processes that mediate species coexistence in diverse co-flowering communities. Here, we examine geographic variation (i.e. at landscape level) in bidirectional pollinator-mediated effects between co-flowering Mimulus guttatus and Delphinium uliginosum. We evaluated effects on pollen transfer dynamics (conspecific and heterospecific pollen deposition) and plant reproductive success. We found evidence of asymmetrical effects (one species is disrupted and the other one is facilitated) but the effects were highly dependent on geographical location. Furthermore, effects on pollen transfer dynamics did not always translate to effects on overall plant reproductive success (i.e. pollen tube growth) highlighting the importance of evaluating effects at multiple stages of the pollination process. Overall, our results provide evidence of a spatial mosaic of pollinator-mediated interactions between co-flowering species and suggest that community assembly processes could result from competition and facilitation acting simultaneously. Our study highlights the importance of experimental studies that evaluate the prevalence of competitive and facilitative interactions in the field, and that expand across a wide geographical context, in order to more fully understand the mechanisms that shape plant communities in nature. 

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2. Modeling scale up of anthropogenic impacts from individual pollinator behavior to pollination systems

   https://doi.org/10.1111/cobi.13754  

   Gegear, Robert J. ; Heath, Kevin N. ; Ryder, Elizabeth F. ( May 2021 , Conservation Biology)

   Understanding how anthropogenic disturbances affect plant–pollinator systems has important implications for the conservation of biodiversity and ecosystem functioning. Previous laboratory studies show that pesticides and pathogens, which have been implicated in the rapid global decline of pollinators over recent years, can impair behavioral processes needed for pollinators to adaptively exploit floral resources and effectively transfer pollen among plants. However, the potential for these sublethal stressor effects on pollinator–plant interactions at the individual level to scale up into changes to the dynamics of wild plant and pollinator populations at the system level remains unclear. We developed an empirically parameterized agent‐based model of a bumblebee pollination system called SimBee to test for effects of stressor‐induced decreases in the memory capacity and information processing speed of individual foragers on bee abundance (scenario 1), plant diversity (scenario 2), and bee–plant system stability (scenario 3) over 20 virtual seasons. Modeling of a simple pollination network of a bumblebee and four co‐flowering bee‐pollinated plant species indicated that bee decline and plant species extinction events could occur when only 25% of the forager population showed cognitive impairment. Higher percentages of impairment caused 50% bee loss in just five virtual seasons and system‐wide extinction events in less than 20 virtual seasons under some conditions. Plant species extinctions occurred regardless of bee population size, indicating that stressor‐induced changes to pollinator behavior alone could drive species loss from plant communities. These findings indicate that sublethal stressor effects on pollinator behavioral mechanisms, although seemingly insignificant at the level of individuals, have the cumulative potential in principle to degrade plant–pollinator species interactions at the system level. Our work highlights the importance of an agent‐based modeling approach for the identification and mitigation of anthropogenic impacts on plant–pollinator systems.

    

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3. Community context mediates effects of pollinator loss on seed production

   https://doi.org/10.1002/ecs2.4569  

   Arrowsmith, K. C. ; Reynolds, Victoria A. ; Briggs, Heather M. ; Brosi, Berry J. ( June 2023 , Ecosphere)

   A critical goal for ecologists is understanding how ongoing local and global species losses will affect ecosystem functions and services. Diversity–functioning relationships, which are well‐characterized in primary producer communities, are much less consistently predictable for ecosystem functions involving two or more trophic levels, particularly in situations where multiple species in one trophic level impact functional outcomes at another trophic level. This is particularly relevant to pollination functioning, given ongoing pollinator declines and the value of understanding pollination functioning for single plant species like crops or threatened plants. We used spatially replicated, controlled single‐pollinator‐species removal experiments to assess how changes in bumble bee species richness impacted the production of fertilized seeds in a perennial herb—Delphinium barbeyi—in the Rocky Mountains of Colorado, USA. To improve predictability, we also assessed how traits and abundances in the plant and bumble bee communities were related toD. barbeyireproductive success. We hypothesized that trait‐matching between pollinator proboscis length andD. barbeyi's nectar spurs would produce a greater number of fertilized seeds, while morphological similarity within the floral community would dilute pollination services. We found that the effects of pollinator removal differed depending on the behavioral patterns of pollinators and compositional features of the plant and pollinator communities. While pollinator floral fidelity generally increasedD. barbeyiseed production, that positive effect was primarily evident when more than half of theBombuscommunity was experimentally removed. Similarly, communities comprising primarily long‐tongued bees were most beneficial toD. barbeyiseed production in tandem with a strong removal. Finally, we observed contrasting effects of morphological similarity in the plant community, with evidence of both competition and facilitation among plants. These results offer an example of the complex dynamics underlying ecosystem function in multitrophic systems and demonstrate that community context can impact diversity–functioning relationships between trophic levels.

    

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4. Evaluating the influences of floral traits and pollinator generalism on α and β diversity of heterospecific pollen on stigmas

   https://doi.org/10.1111/1365-2435.14465  

   Ashman, Tia‐Lynn ; Wei, Na ( November 2023 , Functional Ecology)

   Pollinator sharing often leads to receipt of heterospecific pollen (HP) along with conspecific pollen. As a result, flowering plants can accumulate diverse communities of HP on stigmas. While variation in HP diversity is an important selective force contributing to flowering plant fitness, evolution and community assembly, our understanding of the extent and drivers of heterogeneity of HP diversity is limited.

   In this study, we examined the species compositions and abundances of ~1000 HP communities across 59 co‐flowering plant species in three serpentine seep communities in California, USA. We evaluated the variation in HP diversity (γ diversity) across plant species in each seep and asked whether the variation in HP γ diversity was caused by variation in HP diversity within stigmas (α diversity) or HP compositional variation among stigmas (β diversity) due to the replacement of HP species (turnover) or their loss (nestedness) from one stigma to another. We further evaluated the potential drivers of variation in HP α and β diversity using phylogenetic structural equation models.

   We found that variation in HP γ diversity across plant species was driven strongly by differences among species in HP α diversity and to a lesser extent by HP β diversity. HP community turnover contributed more to HP β diversity than nestedness consistently across plant species and seeps, suggesting a general pattern of HP compositional heterogeneity from stigma to stigma. The phylogenetic structural equation models further revealed that floral traits (e.g., stigma area, stigma‐anther distance, stigma exposure) and floral abundance were key in determining HP α diversity by influencing HP abundance (load size), while floral traits and abundance showed variable impact on HP β diversity (turnover and nestedness). Pollination generalism contributed relatively less to HP‐α and β diversity.

   These findings disentangle the heterogeneity in HP diversity at different levels, which is essential for understanding the process underlying patterns of HP receipt in plant communities. That floral traits drive the heterogeneity in HP diversity points to additional avenues by which HP receipt may contribute to plant evolution.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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5. Biotic and abiotic drivers of plant–pollinator community assembly across wildfire gradients

   https://doi.org/10.1111/1365-2745.13530  

   LaManna, Joseph A. ; Burkle, Laura A. ; Belote, R. Travis ; Myers, Jonathan A. ; Bartomeus, ed., Ignasi ( November 2020 , Journal of Ecology)

   Understanding how abiotic disturbance and biotic interactions determine pollinator and flowering‐plant diversity is critically important given global climate change and widespread pollinator declines. To predict responses of pollinators and flowering‐plant communities to changes in wildfire disturbance, a mechanistic understanding of how these two trophic levels respond to wildfire severity is needed.

   We compared site‐to‐site variation in community composition (β‐diversity), species richness and abundances of pollinators and flowering plants among landscapes with no recent wildfire (unburned), mixed‐severity wildfire and high‐severity wildfire in three sites across the Northern Rockies Ecoregion, USA. We used variation partitioning to assess the relative contributions of wildfire, other abiotic variables (climate, soils and topography) and biotic associations among plant and pollinator composition to community assembly of both trophic levels.

   Wildfire disturbance generally increased species richness and total abundance, but decreasedβ‐diversity, of both pollinators and flowering plants. However, reductions inβ‐diversity from wildfire appeared to result from increased abundances following fires, resulting in higher local species richness of pollinators and flowers in burned than unburned landscapes. After accounting for differences in abundance, standardized effect sizes ofβ‐diversity were higher in burned than unburned landscapes, suggesting that wildfire enhances non‐random assortment of pollinator and flowering‐plant species among local communities.

   Wildfire disturbance mediated the relative importance of mutualistic associations toβ‐diversity of pollinators and flowering plants. The influence of pollinatorβ‐diversity on flowering‐plantβ‐diversity increased with wildfire severity, whereas the influence of flowering‐plantβ‐diversity on pollinatorβ‐diversity was greater in mixed‐severity than high‐severity wildfire or unburned landscapes. Moreover, biotic associations among pollinator and plant species explained substantial variation inβ‐diversity of both trophic levels beyond what could be explained by wildfire and all other abiotic and spatial factors combined.

   Synthesis. Wildfire disturbance and plant–pollinator interactions both strongly influenced the assembly of pollinator and flowering‐plant communities at local and regional scales. However, biotic interactions were generally more important drivers of community assembly in disturbed than undisturbed landscapes. As wildfire regimes continue to change globally, predicting its effects on biodiversity will require a deeper understanding of the ecological processes that mediate biotic interactions among linked trophic levels.

    

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