More than 60% of earth’s terrestrial surface is managed by humans as agriculture, yet little is known about ecological processes within these managed landscapes. Because most organisms are reliant on dispersal to locate resources and mates, the permeability of local landscapes can have extreme impacts on population gene flow, particularly for plants and pollinators.  Bumblebees are one of the most effective groups of crop pollinators and are also among the first species to be lost as natural habitat is destroyed. In this study, we investigate the impacts of local land management on colony density and foraging patterns for the common yellow-faced bumblebee, Bombus vosnesenskii.  Field work was conducted in five agricultural sites and four semi-natural sites in northern California. In each site, we collected 100 bees across a 1km transect and measured floral resource density and diversity. All bees were genotyped at 12 highly variable microsatellite loci to reveal colony identity.

Results/Conclusions

We used the likelihood method employed by the program COLONY v1.3 to reveal significantly higher bumblebee nesting densities in semi-natural habitats than agricultural habitats. Relative colony size was not significantly different between habitat types. Average foraging ranges were similar in semi-natural and agricultural habitats (mean = 1.7 km). Diploid males comprised approximately 2% of the population with a slightly greater proportion of diploid males in agricultural habitats. Overall, our results indicate that B. vosnesenskii exhibits long-distance foraging in both agricultural and semi-natural habitats, but that colony densities are substantially higher in semi-natural habitats. Floral resource availability was substantially greater in semi-natural habitats, and may partially explain greater nesting densities. High genetic diversity levels and low inbreeding levels indicate that this species may be resilient to moderate habitat alteration, despite decreases in colony density.