Floral resource diversity drives bee community diversity in prairie restorations along an agricultural landscape gradient

Abstract

Grassland ecosystems are imperiled by agricultural activity world-wide. Restoring grassland habitat is important to conserving grassland fauna and preserving ecosystem services, but more knowledge is needed on the impact that local and landscape factors have on patterns of diversity. We focused on whether prairie grassland restorations along a gradient of increasing agricultural cover in the surrounding landscape would be inhabited by less diverse and/or more homogenous native bee communities. Native bees are a specific target for many grassland restoration efforts, and supporting their local and β-diversity in reconstructed habitats is of mounting interest. We also investigated if higher floral resource richness within restorations could help ameliorate negative effects of agricultural landscapes. We sampled 16 prairie restorations in Minnesota (USA) that varied along a gradient of increasing agricultural land cover around the site. We characterized floral resource richness at all sites beginning in mid-May and ending in mid-September. We used GLMMs and multivariate analyses to disentangle how floral resource richness and percentage of surrounding land cover in agricultural production are associated with the local and β-diversity of bee communities. Local bee diversity increased with increasing local floral resource richness, independent of the surrounding landscape. Bee β-diversity was not impacted by local floral resource richness or percentage of agricultural cover in the surrounding landscape, indicating local and landscape factors are not substantially impacting the homogeneity of bee communities across restorations. Synthesis and applications. We found that, regardless of agricultural cover in the surrounding landscape, more florally rich plantings attract more diverse bee communities. We recommend that habitat plantings prioritize local scale diversity, and that potential sites where the landscape is dominated by agricultural production should not be overlooked for restoration.