Chicago Bees: Urban Areas Support Diverse Bee Communities but with More Non-Native Bee Species Compared to Suburban Areas

Urbanization is rapidly growing worldwide, yet we still do not fully understand how it affects many organisms. This may be especially true for wild bees that require specific nesting and floral resources and have been threatened by habitat loss. Our study explores the response of wild bee communities to an urbanization gradient in the Chicagoland region of Illinois. Specifically, we explored how both landscape scale impervious surface and local floral diversity across an urbanization gradient influenced 1) the composition of local bee communities, 2) the richness of native and non-native bees, and 3) the composition of bee functional traits. Over the course of our study, we documented 2,331 bees belonging to 83 different species, 13 of which were not native to North America. We found that impervious surface influenced the overall composition of bee communities. In particular, highly urban areas were composed of more non-native bee species and fewer native bee species. Additionally, bee richness and native bee richness responded positively to floral resources. Bee functional trait responses were variable, with floral diverse sites supporting greater richness of ground nesting, eusocial, and generalist bees regardless of landscape-level impervious surface. Importantly, our study provides evidence that urban areas can support diverse bee communities, but urban and suburban bee communities do differ in composition. Thus, bee conservation efforts in urban areas should focus on creating floral diverse habitats to help support more bee species, specifically native bee species, while also considering which bees are best supported by these conservation efforts.