Wild bees in urban grasslands: Urbanisation, functional diversity and species traits

Abstract

While cities are known as important habitats for wild bees, a conceptual understanding of how assemblages of wild bee species are shaped by urban environments is limited. We applied a functional approach to test how taxonomic and functional diversity within wild bee communities of urban grasslands, and traits of bee species, related to local habitat features (e.g., management, species richness, flower coverage) and characteristics of the surrounding urban matrix (e.g., urbanisation, isolation). Surprisingly, urbanisation was not related to any diversity measure. Yet, taxonomic and functional diversity in bee communities, and proportion of endangered bee species, responded negatively to the isolation of grasslands within the urban matrix—but positively to flower coverage. Urbanisation, previous restoration efforts and site type filtered the functional composition of bee communities in terms of species traits related to diet and nesting. Results substantiate the role of urban habitats for functionally diverse bee communities, including Red-Listed species, and indicate pathways towards enhancing habitat functions of urban grasslands for wild bees by (i) improving the connectivity of urban grassland patches within the urban matrix, and (ii) more locally by adjusting management to maintain flower coverage in grasslands. These approaches can support efforts to develop pollinator-friendly greenspaces within the urban green infrastructure.