Honey bee introductions displace native bees and decrease pollination of a native wildflower

Introduced species can have cascading effects on ecological communities, but indirect effects of species introductions are rarely the focus of ecological studies. For example, multiple studies have documented how abundant honey bees impact wild bee communities through competition for floral resources; however, few have quantified how these competitive interactions affect pollination. Using experimental hive additions and field observations in montane meadows, we show that honey bee introductions indirectly reduce pollination of an ecologically important wildflower, Camassia quamash, by competitively excluding visits from more effective bees. Increased honey bee abundance led to decreased nectar and pollen availability, which may explain why native bee visits declined. We demonstrate that honey bee introductions can erode longstanding mutualisms, with negative consequences for plant reproduction. Our study calls for a more thorough understanding of the indirect consequences of species introductions and more careful coordination of hive placements.