Selection for Optimal Fruit-Crop Size in Bird-Dispersed Plants

Abstract

Recent investigations of plant-frugivore interactions have failed to demonstrate the expected peak in fruit-removal rates (plant fitness) at intermediate or high crop sizes. In three species of Costa Rican forest understory plants, I found that the likelihood of bird visitation increased with increasing crop size. Among those plants visited by birds, the absolute number of fruits removed increased with increasing crop size, whereas the proportion, or relative number removed, actually decreased. Thus, effects of crop size on the different components of the dispersal process (likelihood of visitation by birds, fruit removal by those that do visit, and postremoval behavior of dispersers) often conflict, such that no clear relationship between crop size and overall dispersal success is evident. Results presented here suggest selection for synchronous ripening of large seasonal fruit crops in these plants. Nevertheless, I propose that models of the relationship between crop size and reproductive success in tre...