Florida International University, Florida, United States
Background/Question/Methods
Biological invasions can disrupt the composition and function of ecological communities, including plant-pollinator mutualisms. Most introduced bees are solitary, yet there is little understanding of what role naturalized solitary bees have in recipient communities. We investigated changes in pollinator interactions and reproductive output of an endangered buzz-pollinated legume, Chamaecrista keyensis, on a rare island ecosystem in south Florida following naturalization of solitary orchid bees, Euglossa dilemma.Orchid bees were observed to readily sonicate pollen from flowers of the endangered legume. We used a historical dataset (2001) of flower visitation frequencyand reproduction of C. keyensis in the same urban and wilderness areas on the island to assess what effects naturalization of orchid bees had on the plant-pollinator community. Using permutational multivariate analysis of variance tests, we compared pollinator interactions after discovery of the bees on the island (2015) to the historical pollinator community (2001), and we assessed long-term effects of naturalization (2015-2019) on pollinator interactions. To further understand if changes in pollinator visits affected plant reproduction, we compared fruit and seed set in C. keyensis (before-after & long-term after naturalization) using generalized linear models.
Results/Conclusions
We detected high turnover in the pollinator assemblage of C. keyensis after orchid bees arrived on the island (R2 = 0.36, F(1) = 4.55 P < 0.01). Large native carpenter bees, Xylocpa micans, were replaced by orchid bees as the dominant pollinator, and carpenter bees were nearly absent from the assemblage in all years post-naturalization or orchid bees. However, fruit and seeds per fruit in the endangered legume remained unchanged and were consistent throughout the study. Further, the initial pollinator interaction turnover was sustained for the five years of our study, across urban and wilderness areas, and despite an impactful hurricane landfall in 2017 (R2 = 0.12, F(4) = 0.85, P > 0.1). Our study suggests that specialized plant-pollinator relationships are vulnerable to invasions but that replacement by a functional equivalent may maintain adequate pollination. While the naturalized solitary bee does not pose an apparent threat to pollination of the federally endangered C. keyensis, its competitive foraging ability warrants further investigation for managing native pollinators as well as rare plant species.
