Molecular and spatial analyses reveal links between colony-specific foraging distance and landscape-level resource availability in two bumblebee species

Foraging distance is a key determinant of colony survival and pollination potential in bumblebees Bombus spp. However this aspect of bumblebee ecology is poorly understood because of the difficulty in locating colonies of these central place foragers. Here, we used a combination of molecular microsatellite analyses, remote sensing and spatial analyses using kernel density estimates to estimate nest location and foraging distances for a large number of wild colonies of two species, and related these to the distribution of foraging habitats across an experimentally manipulated landscape. Mean foraging distances were 755 m for Bombus lapidarius and 775 m for B. pascuorum (using our most conservative estimation method). Colony-specific foraging distances of both species varied with landscape structure, decreasing as the proportion of foraging habitats increased. This is the first time that foraging distance in wild bumblebees has been shown to vary with resource availability. Our method offers a means of estimating foraging distances in social insects, and informs the scale of management required to conserve bumblebee populations and enhance their pollination services across different landscapes.