The Role of Frugivores in Determining Seed Removal and Dispersal in the Neotropical Nutmeg

Abstract

At the Nouragues field station (French Guiana), we studied the seed dispersal system of two sympatric tropical tree species that differ in seed size, Virola kwatae and V. michelii (Myristicaceae), to evaluate the degree of interaction between Virola species and their dispersers, and consistency in the fruit traits affecting seed removal rate. Only the spider monkey ( Ateles paniscus) and three species of ramphastid toucan dispersed the large (4.8g) V. kwatae seeds. These four animal species, as well as three smaller-bodied bird species, also dispersed the small V. michelii seeds (2.1g). Annual fecundity of both Virola species did not affect seed removal rate. However, variation in V. kwatae seed size within tree populations, and increased seed removal rate due to fruit selection on seed size, suggest a potential for an evolutionary response of seed size to selection by large-bodied frugivores in this species. In contrast, seed size did not affect V. michelii seed removal rate, and the interactions between V. michelii and its dispersers are interpreted to be too diffuse to result in strong selection on plant traits affecting seed removal rate. Because hunting pressure is greater on larger than on smaller frugivores, extinction of A. paniscus (the main large-bodied seed disperser of the study Virola) is likely to affect the long tail of dispersal kernel, thus decreasing recruitment away from fruiting adult trees.