Effects of habitat fragmentation on bumblebee foraging trip duration and colony fitness

Abstract

Agricultural intensification with the associated habitat loss and fragmentation are among the most important drivers for the dramatic loss of wild pollinators. In this study, conducted in intensively managed vineyards in southern Switzerland, we tested the interdependent effects of habitat amount (surface of vegetated vineyards per landscape) and fragmentation (number of vegetated vineyards per landscape) on fitness-relevant traits in bumblebee Bombus terrestris terrestris colonies. Individual bumblebee foraging trips were measured with RFID (radio frequency identification) technology while colony fitness was assessed by quantifying nest parameters related to colony size. Vegetation cover in vineyards showed an overall positive effect on colony fitness and foraging behaviour. More specifically, colony fitness was strongly driven by an interactive effect of habitat amount and fragmentation: the degree of fragmentation had a negative effect on bumblebee colony fitness when the amount of habitat was low, while it positively affected colony fitness in landscapes with high amounts of habitat. These results highlight the interdependency of habitat amount and fragmentation on a pollinator’s fitness with its concomitant consequences on management recommendations. Whenever habitat amount is low the surface of vegetated vineyards should be increased and aggregated whereas mosaic-like habitats composed of different management styles should be created when habitat amount is high.