Impacts of a naturalized specialist bee Centris nitida on an endemic mutualism in Southern Florida

Background/Question/Methods

Recently, a specialist oil-collecting bee, Centris nitida, native to Mexico and Central America has been reported to be naturalized in urban areas and pine rocklands of southeastern Florida. In 1998, C. nitida was observed to visit the flowers of the rare endemic plant, Byrsonima lucida, the only member of the tropical plant family Malpighiaceae native to southern Florida. The B.lucida flowers offer oils as a pollinator reward which is collected by Centris errans, the sole Centris species native to southern Florida. This study will assess the impacts of the invasive oil-collecting bee on this native specialized mutualism. Understanding the nature of these novel relationships is vital for the conservation of B. lucida and the overall ecosystem health of the pine rocklands. We have selected for the study four natural areas where only C. errans is present, and four areas where both bees were present in previous reports. This study examined the breeding system of B. lucida, assessed the degree of pollination limitation in B. lucida, and compared pollination efficiencies, visitation frequencies, and foraging rates of the Centris bees.

Results/Conclusions

Breeding system results showed that B. lucida was self incompatible (P = 0.042), pollinator dependent (pollinator excluded flowers failed to set fruit), and the stigmas of the red flowers were the least receptive (P = 0.009). There was a significant difference in mean fruit set among all pollination treatments at sites where both bees occur (P = 0.005). Pollination limitation treatments suggested that B. lucida was pollen limited in all study sites (P < 0.001), regardless of the contributions of the additional pollinator services (P = 0.879). The native oil bee had significantly higher visitation rates (P = <0.001) but has a lower foraging rate (P = < 0.001) and was a less efficient pollinator (produced lower mean fruit set) than the invasive oil bee. Overall, this study found the invasive oil bee to be less common than previously described and it did not appear to be competing with the native oil bee or impacting its established obligate mutualism.