Summary　Response of bumblebee community to overabundant Hokkaido sika deer (Cervus nippon yesoensis)

Abstract

In this study, we assessed the influence of high-density populations of the Hokkaido subspecies of sika deer (Cervus nippon yesoensis) on the abundance, species richness, and species composition of bumblebee communities. We collected bumblebees and recorded number of flowering plants at three study plots in a high-deer density area (Nakajima Island, located inside Lake Toya, southwest Hokkaido) and in a nearby low-deer density area (forests surrounding Lake Toya). Although species richness did not differ between these areas, bumblebee abundance on Nakajima Island was significantly lower than that in lakeside forests. Species composition of bumblebee communities in the two areas was found to significantly differ using nMDS analysis ; the abundance of Bombus hypocrita sapporoensis, the dominant species in both areas, was lower on Nakajima Island, and the abundance of other bumblebee species was low as well. Furthermore, on Nakajima Island the number of flowering plants was low and floral phenology had a pattern of temporary interruption. These results suggest that high deer density influenced the bumblebee community through vegetation modification and temporary interruption of normal floral phenology.