Conclusions
Our findings bear on ongoing discussion about permitting of honey bee hives on public lands. Historically, the placement of managed hives in U.S. National Forests and Parks has been restricted and tightly regulated. However, beekeepers have successfully lobbied to have honey bees considered a “non-consumptive” use of U.S. National Forest land (U.S. Code of Federal Regulations 2013). If adopted widely, such changes will likely lead to a massive increase in the number of managed honey bees in natural areas. Although honey bees are important pollinators in other systems, we show that indirect negative effects of competition can lead to overall negative effects of honey bee introductions on pollination. As such, introducing hives to sensitive ecosystems should be approached with extreme caution.
More fundamentally, we show that introduced pollinators can disrupt plant-pollinator mutualisms and impair ecosystem functioning. These mutualists, although infrequently studied in the invasive species literature, broadly meet the definition of an “invasive” species (IUCN 2018) despite their economic benefits to human society. Untangling direct and indirect effects allowed us to mechanistically understand the functional consequences of honey bee introductions. We therefore recommend that future studies carefully consider indirect impacts of introduced and invasive species as biodiversity continues to decline and ecological communities become increasingly homogenous.