COS 162-4 - Local and landscape factors influence plant-pollinator networks and bee foraging behavior across an urban corridor

Background/Question/Methods

With widespread concerns over bee declines due to urbanization, maintaining natural habitat within urban areas can promote bee diversity across otherwise resource poor environments. However, natural habitats are highly heterogenous in their composition, quality, and connectivity, which can affect bee communities and alter plant-pollinator interactions. As many flowers within natural areas rely on pollinators for successful pollination, plant-pollinator networks can provide insight into community stability and ecosystem function, thus allowing us to determine how to effectively manage urban habitats to maximize pollination.

We conducted a study across two rapidly growing metroplexes to determine which local and landscape-level factors affect pollinators within urban grasslands. We asked: 1) what are the local and landscape drivers of bee abundance, species richness, and plant-pollinator networks? and 2) do bees show preferences for specific flowering species? We visited 20 grasslands 3 times throughout the flowering season to collect bees via hand-netting and measure site-level composition. We swabbed bees for pollen to create pollen-based plant-pollinator networks and to examine flower preferences. Finally, we calculated the amount of semi-natural habitat and habitat heterogeneity within 2 km of each grassland. We ran generalized linear mixed models to examine local and landscape effects on network specialization, generality, and connectence.

Results/Conclusions

Through the examination of pollen-based networks and a pollen preference analysis, our study provides much needed insight into bee foraging behavior across urbanizing landscapes. Though we did not find any local or landscape effects on bee abundance or species richness, we did find that plant-pollinator networks were driven by the landscape surrounding our sites, though floral abundance and vegetation within sites were important as well. Specifically, bees exhibited higher specialization with increased habitat heterogeneity and visited on average fewer flowering species (generality) with increasing amounts of semi-natural habitat surrounding our grassland sites. However, within the grassland sites, we found that bees visited more plant species on average with increased floral abundance. Finally, we found that connectance decreased with increased amount of vegetation within sites. Our pollen preference analysis for 5 of our most common bee species revealed species-specific flower preferences, which highlights the need for maintaining high flowering diversity across natural habitat to maximize pollinator diversity. Overall, our findings show that maintaining floral resources within urban areas and providing natural habitat on a larger scale surrounding rapidly developing areas will provide food and nesting resources for bees and maintain pollination services.