While many bee species are declining, managed species, such as honey bees, have been introduced into novel ecosystems across the globe. Many studies support the claim that introduced honey bees compete with native bees for floral resources. However, little is known about how honey bee introductions affect native plants. Studying the impact of honey bee introductions is an important issue for native plant conservation because honey bee presence can alter native bee community composition, abundance, and behavior, which may disrupt native plant pollination. We studied the impact of honey bee introductions on the pollination and reproduction of a Sierra wildflower, Camassia quamash. We sampled meadows along a gradient in honey bee abundance generated by experimental honey bee introductions and pre-existing apiary locations to ask whether increased honey bee abundance in the landscape affected plant-pollinator interactions, the composition of the community of insects visiting focal C. quamash plants, and patterns of pollen deposition and seed set. We also investigated whether honey bees were good pollinators of C. quamash by conducting a separate experiment in which we manipulated the number of honey bee visits flowers received.
Results/Conclusions:
We found that increased honey bee abundance in the landscape leads to increased visitation to C. quamash by honey bees and decreased visitation by native bees, potentially indicating competitive exclusion. Preliminary results also suggest that honey bees are ineffective pollinators of C. quamash on a per visit basis and this inefficiency is not compensated for by an increased number of honey bee visits. The replacement of native bee visits by honey bee visits correlated with reduced seed set, suggesting that honey bee introductions in the Sierra may have negative effects on the pollination of C. quamash. This research demonstrates that honey bee introductions can have negative effects on plant pollination when they lead to an over-representation of visits from ineffective pollinators.