Honeybees have consequences for foraging bumblebees in Irish heathlands

Abstract

Heather provides vital forage for wild bumblebees, as well as managed honeybees that are brought to heathlands in late summer for honey production. With this increased honeybee activity, there is potential for competition for floral resources between honeybees and bumblebees. We studied whether increasing numbers of honeybee hives in upland heathlands influenced honeybee abundance, nectar availability and bumblebee abundance, size, species composition, flower handling time and pollen collection at two distances from the honeybee hives. More hives resulted in more honeybees but had no impact on bumblebee abundance or the relative dominance among bumblebee species. However, more hives resulted in shorter flower handling times and an increased proportion of pollen-collecting bumblebees, potentially to compensate for reduced resource availability. Bumblebee worker size declined with the number of hives, suggesting either displacement of larger workers as a means to escape competition, increased recruitment of small foragers to compensate for smaller rewards, or a combination thereof. Our results show that honeybees can alter bumblebee foraging even in resource-rich environments. This highlights the need to assess long-term population effects and consider interactions between wild and managed bees in management and conservation to ensure both the protection of wild bumblebees and profitable honey production.