UC San Diego

Honey bees are the most widespread pollinating animal species in natural plant communities worldwide, and in San Diego, California, despite high native bee diversity, the introduced honey bee is responsible for over 75% of flower visits. We performed a) a meta-analysis of published studies which report the per-visit efficiency of honey bees as pollinators relative to other floral visitors and b) a field survey documenting seasonal change in floral abundances and pollinator visitation in a coastal sage scrub (CSS) system in San Diego, in order to better understand the importance of honey bees as pollinators in natural communities. We found that, although honey bees were less efficient than the top non-honey bee pollinator, their efficiency did not differ from the average of non-honey bee floral visitors, and after factoring in visitation frequency, honey bees were no less important. Furthermore, in a San Diego system where honey bees are the numerically dominant floral visitor, we found that honey bees almost exclusively visit the most abundantly flowering species and increase their numbers rapidly as floral abundance increases. By contrast, non-honey bees were fairly indiscriminate floral visitors and only responded to the changes in floral abundance of some plant species with low overall floral abundance. Therefore, although in natural communities honey bees generally provide average pollination services for the plant species they visit, preference for, and recruitment to species with abundant flowers may mean that plant species with lower floral abundance within these systems depend on the pollination services of non-honey bee floral visitors.