Native bee genus diversity within bee-friendly urban gardens varies little along an urbanization gradient

Urban bee populations are threatened by ongoing habitat loss and fragmentation. Bee-friendly gardens with abundant forage and nesting resources may help offset these pressures, but attributes of the broader urban landscape could also play an important role. We explored bee diversity within 32 bee-friendly gardens distributed throughout the city of Kelowna, British Columbia. Our objectives were to (i) estimate bee genus abundance, richness, and composition within the gardens, and (ii) investigate how these facets of diversity varied with plant diversity, garden size, and degree of urbanization within 300 m of the garden. In total, over 10 sampling days per garden, we observed 19 genera—about half of those known from the region—primarily within the Halictidae family (66.4% of total abundance). Neither bee genus richness nor total bee abundance was associated with any of the explanatory variables, whereas a minor (though statistically significant) percentage of the among-site variance in genus composition was uniquely accounted for by the urbanization gradient (6.8% with rare genera excluded, 5.8% when included). Our study is the first to evaluate urban bee diversity within the Okanagan diversity hotspot and our findings add to previous studies elsewhere demonstrating inconsistent effects of garden and landscape-scale characteristics on bee diversity.