While urbanization has caused significant habitat loss, the absence of pesticides and monocultures in urban areas has caused cities to become refuges for native bee communities. Great diversity and abundances of bees across many families and genera are found foraging in urban farms and community gardens throughout cities, including St. Louis, Missouri. An additional source of city vegetation, green roofs, may mitigate water run-off, improve aesthetics, and minimize the urban heat island effect. In St. Louis, the Food Roof Farm goes a step further, effectively turning their green roof into a small urban farm providing locally grown produce. The goal of this research was to characterize the bee communities found on this roof and two other green roofs in the city. Collections of bee specimens (Anthophila) were conducted over two years via weekly samplings of each roof. By tracking abundances and measures of diversity on these roofs compared to ground-level community gardens nearby, we can assess the ecological impact and conservation value of these novel habitats. We also wanted to determine if the bee community found in these roofs is a random sample of the general community found at ground level or if it represents a non-random nested subset.
Results/Conclusions
Specimen collections took place over a total of 17 collection days. Ten of these were done during the spring/summer of 2017, and seven were done during the spring/summer of 2018. In total, 889 bee specimens were collected from green roofs. The average number of individuals collected per sampling was significantly higher on the Food Room Farm (mean = 31.59 +/- 10.37) than on the two other green roofs. Individuals represented five taxonomic families and eighteen genera including species of social bees, solitary bees, and kleptoparasitic bees. Twenty-four unique species could be identified, but some smaller and harder to identify individuals were identified only to genus. Taxa that were significantly underrepresented on roofs were the family Andrenidae, the genera Hylaeus and Colletes, and species with specific pollen preferences. Specialists like the hibiscus bee (Ptilothrix spp.) and squash bee (Peponapis spp.) were absent on roofs, as well as bees that pollinate flowering trees like Andrena spp. The overall community structure in the Food Roof does not represent a random assortment of species drawn from the city’s species pool. Which specific environmental filters and/or species traits are acting upon our observed community still needs to be determined.