The impacts of species introductions on plant-pollinator network interactions

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Plants form the basis of most terrestrial ecosystems. Approximately 85% of plant species require an animal pollinator to reproduce and persist. However, due to a plethora of largely human driven stressors, pollinators are considered to be at risk globally, with potentially devastating consequences for global ecosystems. Over the past few decades, ecologists have produced a body of literature linking anthropogenic stressors to declining abundance and diversity of pollinator communities, but much less attention has been paid to the impacts of such changes for plant-pollinator interactions. Nonetheless, adding flowering plants to a community is an increasingly common restoration approach, with the goal of enhancing plant-pollinator interactions across a variety of ecosystems. Surprisingly, a recent meta-analysis found no consistent impact of such planting schemes (i.e., hedgerows or floral strips) on the pollination of nearby plants, indicating that there are many gaps in our understanding of how changes to either plant or pollinator communities impact their interaction networks and affect pollination services. The proposed research program will make use of a park restoration scheme recently initiated across the City of Vancouver. My long-term objective is to improve our understanding of how enhancements to the local plant community can impact the growth, stability and persistence of plant-pollinator interactions, which has policy implications for how ecosystems are managed. I hypothesize that the variation in outcomes is partly due to a lack of attention to trait matching between enhancements and the existing community. Ideally, enhancing plant communities will lead to increased colonization and reproduction by local pollinator species, thereby increasing the diversity and strength of their interaction networks. In order to test the long-term dynamics of plant-pollinator interactions, we will gather detailed information about plant traits and pollination networks at treatment (wildflower-enhanced) parks and compare them to control parks over multiple seasons. Using information about the stability of the networks based on their modularity (degree to which the network is composed of interacting subunits) and nestedness (degree to which internal networks are a subset of a larger network), we will examine how networks change over time following enhancements with varying plant-pollinator trait overlap. To test the hypothesis that floral enhancements impact bee reproductive output (a key assumption), we will use artificial nest traps to measure changes in the reproductive output of a set of local native bee species over time. Finally, to explore the impacts of novel bee species introductions, we will use the recent accidental greenhouse introduction of a new species of generalist pollinator, the common eastern bumblebee (Bombus impatiens) to the lower mainland of BC in order to study the impacts of disturbance to the bee community on network dynamics.