by José J. Fumero-Cabán, Elvia J. Meléndez-Ackerman and Julissa Rojas-Sandoval
Flowers, details of
and visitors of Guaiacum sanctum in the Caribbean.
Islands often have plants with reproductive mechanisms allowing for self-compatibility and low species-rich communities of pollinators. Islands are also areas more prone to extinction and vulnerable to invasive species than mainland ones. In this study, we document different reproductive traits of the tropical tree Guaiacum sanctum on two insular populations in the Caribbean with contrasting pollinator assemblages: Guánica on the main island of Puerto Rico where the alien honeybees (Apis mellifera) were first reported in 1994 and Mona Island where honeybees do not occur. On these two islands, we performed a series of field observations and pollination experiments over a period of three years, to assess pollinator species richness, visitation rates, breeding system, and the fitness of selfed- vs. crossed-progenies. We found that flowers are pollinated by insects on both islands, but while the richness of pollinators was higher on Mona, the visitation rates were considerably higher in Guánica where trees are almost exclusively visited by the introduced Apis mellifera. Pollinations experiments show that outcrossing treatment yielded nearly twice the number of fruits and seeds than selfing treatment and these differences are consistent between populations, which might reflect early acting inbreeding depression, partial self-incompatibility, or differences in resource allocation between selfed and outcrossed fruits. Overall, our results suggest that the substantial reduction in pollinator visitors in areas dominated by alien honeybees may add an additional level of vulnerability to these threatened populations.