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.