Landscape context affects both capture probability and abundance of solitary bees in cities

It is intuitive to hypothesize that urban landscapes are broadly hostile to insects, but responses of wild bees to urbanization are inconsistent and often positive. We used a mark-recapture study of the bicolored sweat bee (Agapostemon virescens) to separate two possible causes of this pattern: differences in capture probability (bees are more attractive to sampling sites in low-resource areas) from patterns of true abundance (bees are equally abundant in high- and low-resource landscapes, as long as resources are present locally). To distinguish these possibilities, wee placed experimental patches of Echinacea purpurea, a favored floral resource, in and near community gardens along a landscape gradient of % impervious surface. We collected mark-recapture data of A. virescens visitation to these patches, and analyzed capture probability and abundance in relation to % impervious surface in the surrounding landscape, and local resource context, measured as inside or outside the community garden in low-resource settings (pavement, mulch, or turf grass).  This study took place in the cities of Cambridge, Somerville, and Medford, Massachusetts, USA, which are part of the greater Boston metropolitan area.  We found that capture probability was higher in low-resource contexts (outside of gardens and/or in landscapes with a high % impervious surface).  Fewer individual bees visited patches in non-garden sites and landscapes with high impervious surface, but those bees visited the patches more often.

In addition, all of our experimental patches were used by A. virescens. These data include the capture histories of individual bees, and the characteristics of the sites and community gardens.