Unique Bee Communities within Vacant Lots and Urban Farms Result from Variation in Surrounding Urbanization Intensity

We investigated the relative importance of vacant lot and urban farm habitat features and their surrounding landscape context on bee community richness, abundance, composition, and resource use patterns. Three years of pan trap collections from 16 sites yielded a rich assemblage of bees from vacant lots and urban farms, with 98 species documented. We collected a greater bee abundance from vacant lots, and the two forms of greenspace supported significantly different bee communities. Plant-pollinator networks constructed from floral visitation observations revealed that, while the average number of bees utilizing available resources, niche breadth, and niche overlap were similar, the composition of floral resources and common foragers varied by habitat type. Finally, we found that the proportion of impervious surface and number of greenspace patches in the surrounding landscape strongly influenced bee assemblages. At a local scale (100 m radius), patch isolation appeared to limit colonization of vacant lots and urban farms. However, at a larger landscape scale (1000 m radius), increasing urbanization resulted in a greater concentration of bees utilizing vacant lots and urban farms, illustrating that maintaining greenspaces provides important habitat, even within highly developed landscapes.