As the global human population continues to increase, the populations of cities are expected to rise disproportionately to surrounding rural areas. Typically, specialists are rare in urban settings where the unpredictable availability of resources favor generalist diets. However, little attention has been given to the role of pollen specialists in an urban setting where resources are not always readily available. Ptilothrix bombiformis is a solitary ground-nesting bee species within the Emphorini tribe of the family Apidae (Hymenoptera: Apoidea). The bees specialize on specific families of plants for their pollen, including the Malvaceae and Convolvulaceae families. Three populations of Pt. bombiformis were observed to see how specialist bee behavior changes across an urban to rural gradient. Additionally, we characterized the habitat at each site location - urban, suburban, and rural. We hypothesize that urban specialist bees are more plastic in their response to available resources – both due to the greater variety and the unpredictability of plants in urban areas.
Results/Conclusions
Preliminary results from 36 bees indicate pure pollen loads of Hibiscus spp. on female Pt. bombiformis at all sites during the Hibiscus spp. bloom period. Female Pt. bombiformis were actively provisioning pollen three weeks before the Hibiscus spp. bloomed at the sites. The urban bee population sought Hibiscus spp. at locations outside of their nesting site before and after flowers finished blooming, instead of using the available floral resources at the site. Males were found to carry mixed loads of Hibiscus spp. and other flowers – indicators of their varied nectar diet. The largest population (Shaw; rural) had the highest amount of available pollen, but the lowest diversity of floral resources. Due to the extensive horticultural plantings, the suburban site had the largest diversity of floral resources yet the smallest Pt. bombiformis population. The pollen specialist bee provides an opportunity to test ecological theories of habitat selection and optimal foraging in an urban setting. Future research will focus on multiple specialist bees and exclusion experiments between the bees and their preferred flowers.