Homogenization of taxonomic, phylogenetic, and functional characteristics of bumble bee communities at regional scales in anthropogenic landscapes

Biotic homogenization has been documented following extensive anthropogenic landscape change such as urbanization and agriculture, but diverse native communities also have been reported in these ecosystems. Understanding the influence of landscape-level characteristics on processes of community assembly can inform how human-dominated landscapes shape the structure and composition of local communities, including important pollinators such as bumble bees (Bombus spp.). The objective of this study was to investigate multi-scale patterns of taxonomic, phylogenetic, and functional beta- diversity of bumble bees in greenspaces along an urban-agricultural gradient to understand landscape- scale constraints on processes of community assembly. Bumble bees were collected in greenspaces along an urban-agricultural gradient in Madison, WI, USA. Patterns of biotic homogenization were investigated using measures of beta-diversity and null models relative to a regional bumble bee species pool in a 100 km area surrounding the city. Nine of the expected 13 species from the regional pool were collected in greenspaces in urban and agricultural landscapes. At the regional scale, we found evidence of taxonomic, phylogenetic, and functional homogenization among bumble bee communities in urban and agricultural landscapes, with species that were smaller in size, had shorter wings, were less hairy, but had larger eyes and longer setae on the corbicula (pollen-carrying hind legs) being more common than expected based on null models. When we evaluated filtering from the anthropogenic species pools (i.e., urban and agricultural) to local greenspaces, we found nuanced differences among land cover types, wherein agricultural landscapes supported higher beta-diversity of bumble bee communities than expected while urban landscapes continued to show signals of homogenization. Overall, anthropogenic landscapes acted as a strong filter for bumble bees, broadly selecting for a subset of functionally similar and phylogenetically related species that resulted in homogenization of communities within the region. Our findings support a landscape-level approach to biodiversity conservation that promotes diversifying landscapes to support diverse pollinator populations. OPEN RESEARCH STATEMENTData and novel code associated with this submission are provided in an external repository to be evaluated during the peer review process and are available at https://github.com/kiperry/WI_Bumble_Bees. If this paper is accepted for publication, data and code will be permanently archived within a linked Zenodo repository.