Effects of urban land cover on community composition in Bombus spp.

Bumble bees (Bombus spp.) are essential pollinators for wildflowers, crops and ornamental plants throughout the world. Over the past several decades, over 25% of North America's bumble bee species have severely declined in abundance and geographical range. Habitat loss and fragmentation resulting from urbanization, particularly impervious surfaces, are potential drivers of these declines. Prior research has examined how impervious surface cover impacts bumble bee diversity and abundance, but urban filtering of bumble bees is less studied, and little is known about how different species vary in their susceptibility to these impacts. Furthermore, the effects of impervious surfaces on bumble bee genetics and dispersal remain relatively unexplored. We evaluate the relative abundance of Bombus impatiens, B. griseocollis and B. bimaculatus workers along an urban-to-rural gradient in Madison, WI. We hypothesize that the relative abundance of B. impatiens would be positively correlated with impervious surface cover, based on prior evidence that B. impatiens may be better adapted to urban environments than other Wisconsin species. We also discuss work currently in progress examining genetic structure, allelic diversity and heterozygosity among populations of these three bumble bee species, and how these factors are impacted by impervious surface cover surrounding each population. Here, we hypothesize that impervious surface cover 1) correlates positively with genetic differentiation between populations, and 2) correlates negatively with allelic diversity and heterozygosity within each population. Identifying the impact of impervious surfaces on bumble bee genetics will provide critical data on species and population health and inform future conservation efforts.