Professor University of California Davis, California
Human-mediated species introductions provide real-time experiments in how communities respond to interspecific competition. For example, managed honey bees (Apis mellifera) have been widely introduced outside their native range and may compete with native bees for pollen and nectar. Indeed, multiple studies suggest that honey bees and native bees overlap in their use of floral resources. However, for resource overlap to negatively impact resource collection by native bees, resource availability must also decline, and few studies investigate impacts of honey bee competition on native bee floral visits and floral resource availability simultaneously. In this study, we investigate impacts of increasing honey bee abundance on native bee visitation patterns, native bee pollen diets, and nectar and pollen resource availability in two Californian landscapes: wildflower plantings in the Central Valley and montane meadows in the Sierra. In both systems, honey bee competition increased niche overlap between honey bees and native bees while decreasing pollen and nectar availability. Honey bee competition also led to important shifts in the network of interactions between native bees and plants. In the Sierra, native bees re-shuffled their interactions to escape competition, leading to a decrease in perceived apparent competition (PAC) when networks were compared against randomly re-assembled networks. Thus, although native bees can adapt to honey bee competition by shifting their floral visits, the coexistence of honey bees and native bees is tenuous and will depend on floral resource availability. Preserving and augmenting floral resources is therefore essential in mitigating negative impacts of honey bee competition
