Honey bee (Apis mellifera L.) and wild bee resource competition: how big is this problem?

The Western honey bee (Apis mellifera L.) has been managed by humans for centuries for honey, wax, and most recently, crop pollination. The deep history of human association with this species has enabled agricultural practices that reduce biodiversity of pollinating wild bees, largely through habitat modification. However, there is also interest in determining if Apis mellifera presence itself contributes significantly to wild bee population declines. Here we review the evidence of Apis mellifera effects on wild bees, with a particular emphasis on critically evaluating the evidence for detrimental impacts associated with resource competition. Despite accelerated research in this area, only ∼13% of resource competition studies evaluated fitness effects of Apis mellifera on wild bees, a research gap that has persisted for over 20 years. About three times as many studies have evaluated effects of Apis mellifera on wild bee community parameters, including wild bee abundance, which provides a measure of a landscape's "bee carrying capacity". Just over 20% of these studies show a negative correlation with Apis mellifera abundance. In a novel analysis of 68 additional studies measuring bee communities for a variety of other reasons, we found negative correlations between Apis mellifera abundance and any measure of the wild bee community (richness, abundance, etc.) for nine, and the measures showing Apis mellifera impacts were varied. For example, only two of these studies showed negative correlations between Apis mellifera and wild bee abundances. In contrast, we also found similar numbers of positive relationships between Apis mellifera and various wild bee community parameters, including ten studies that showed positive relationships between Apis mellifera and wild bee abundances. Most studies (64%) showed no relationship with any factor. We found no clear pattern to explain which habitat types are more vulnerable to Apis mellifera competition, nor is the literature clear on impactful densities of managed hives in particular environment types. We discuss suggestions for future research, as well as ways the research community could clarify its conservation priorities with respect to resource competition. Resource competition between Apis mellifera and wild bees is clearly a concern in some cases. However, more work is needed to identify and predict where Apis mellifera poses a significant threat to wild bee populations. Overall, the data do not support a generalized and widespread negative relationship between Apis mellifera abundance and wild bee community health. Rather, conservation measures that reliably improve wild bee health (habitat preservation and restoration) will likely have positive effects on Apis mellifera, and vice versa.