Pollinator nesting and foraging dynamics in human-altered landscapes

Background/Question/Methods

Given widespread declines in managed and native pollinator communities and increasing global reliance on pollinator-dependent crops, there is an acute need to develop a mechanistic understanding of native pollinator population and foraging biology.  Bumble bees (Bombus spp) are one of the most effective native pollinators, and are often the first to be extirpated in human-altered habitats, yet we know little about what landscapes promote their nesting and foraging biology.  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 four agricultural sites and four semi-natural sites in northern California.  In each site, we collected 100 bees across a 1.2km transect and measured floral resource density and diversity. We used a population genetics approach to determine the impacts of habitat composition and floral resource levels on nesting and foraging patterns across natural and human-altered landscapes.

Results/Conclusions

Our findings demonstrate that bumble bee foraging is more plastic and extensive than previously believed, and is not dependent on surrounding habitat composition.  Rather we show that bumble bees forage further in pursuit of species-rich patches and within sites where landscape scale floral resources are more homogenous, regardless of habitat composition.  Further, we find a negative local scale impact of paved habitat and a positive, landscape scale impact of natural woodland on native bee nesting densities.  Overall, this study demonstrates that both natural and human-altered landscapes can be managed for increased native bee nesting and extended foraging, thereby dually preserving biodiversity and enhancing the spatial extent of pollination services.