Phylogenetic homogenization of bee communities across ecoregions

Aim Land use change reorganizes local communities, resulting in complex changes in biodiversity at larger scales. The biotic homogenization hypothesis predicts that the replacement of sensitive loser species with widespread winner species will lead to loss of beta diversity and ultimately loss of regional diversity at multiple levels of ecological organization. We ask if land use is associated with biotic homogenization patterns in bee communities at two large spatial scales, using both species and phylogenetic dissimilarity indices. Location Time period North-eastern USA (New Jersey, New York and Pennsylvania). 2013-2015. Major taxa studied Methods Superfamily Apoidea (bees). We sampled bee communities from replicated sites in forest, agriculture and urban land use types within a large spatial extent spanning four distinct ecoregions. We compared pairwise compositional dissimilarity within and between ecoregions, using both species and phylogenetic dissimilarity indices. We also investigated how compositional difference is related to geographic distance between sites. Results Main conclusions Forested, agricultural and urban landscapes did not differ detectably in either mean pairwise species dissimilarity or slope of distance-decay. Dissimilarity among both agricultural and urban bee communities increased with geographic distance. However, urban landscapes had significantly lower phylogenetic pairwise dissimilarity, indicating strong phylogenetic homogenization at within- and between-ecoregion scales. We did not detect bee species homogenization in agricultural or urban land use types. However, urban land use was associated with phylogenetic homogenization across a large regional extent. Urban bee communities are dominated by closely related species that maintain beta diversity at the species level, but contribute to low phylogenetic beta diversity relative to forest and agricultural bee communities. We observed similar levels of homogenization at landscape and regional spatial extents, despite inter-site distances differing by an order of magnitude between these scales. Further urbanization could result in loss of bee biodiversity and evolutionary history at multiple spatial scales.