Floral species evenness is the major driver of wild bee communities in urban gardens

Urban gardens have the potential to contribute to urban bee biodiversity. However, studies considering the effects of habitat amount and floral resources on bees using a functional approach, are largely lacking in Latin America, in particular in urban environments, where the potential competitive interactions between honeybees and wild bees deserve further attention. We evaluated how bee abundance and diversity, both taxonomic (richness, evenness) and functional (richness, evenness, and divergence of traits), are related to habitat amount in urban gardens (patch size, green cover in the surroundings), and the abundance and diversity of flowers (taxonomic and functional). We also examined the effect of the abundance of honeybees on urban wild bee communities. We selected 13 gardens within Cordoba city (Argentina) along an urbanization gradient based on vegetation cover, where we surveyed bee-flower interactions. We selected flower (i.e. morphology, color, and phenology) and bee (i.e. morphology, sociality, and diet) traits considered essential to plant-pollinator interactions to estimate flower and bee functional diversity, respectively. Bee taxonomic and functional diversity in urban gardens strongly depended on the floral species evenness, whereas the functional floral diversity and patch size, as well as the habitat amount at the landscape scale, did not significantly affect bee diversity. Moreover, the abundance of honeybees, once controlled by floral species evenness, did not influence the taxonomic structure of wild bee communities. Our results highlight that urban gardens can support functionally diverse bee communities, especially those with evenly distributed flower species.