A disponibilidade de diásporos ornitocóricos em uma floresta tropical influencia o consumo desses diásporos tanto por aves frugívoras como por insetos predadores de sementes?

Abstract

Most tropical plants have fruits and seeds attractive to birds (ornitochorous diaspores). In addition to diaspore characteristics, plants might attract frugivore birds by fruiting intensively, which in turn might attract seed predator insects (granivores). Pre-dispersal seed predation might decrease diaspore attractiveness to frugivores and thus negatively influence seed dispersal. Because the scientific literature reports different relationships of diaspore consumption by frugivores and by granivores as a function of diaspore availability, here we describe this relationship for three tropical ornitochorous tree species. For this, we used the seed rain collected monthly during a 1-yr period in a 1-ha plot installed at the Lowland Tropical Rainforest in the north coast of the State of São Paulo, SE Brazil. We selected the three most abundant ornitochorous tree species in the seed rain (Euterpe edulis, Hieronyma alchorneoides e Mollinedia schottiana) and checked their diaspores in order to identify if they were intact, if they were consumed by frugivores and/or if they were predated by insects. Then, we determined if there was a relationship of the number of diaspores consumed by frugivores and by granivores with the number of diaspores available in the seed rain throughout the year. We also determined whether frugivores consumed diaspores lacking predation marks in greater proportion than diaspores with marks of predation. The consumption of diaspores by frugivores and by granivores increased with the number of diaspores available, with the exception of predation of E. edulis. Frugivores consumed diaspores lacking predation marks in greater proportion than diaspores with marks of predation. For E. edulis and M. schottiana, the proportion of diaspores with marks of frugivory only was higher than the proportion of diaspores lacking predation marks, indicating that birds, which are especially visually oriented, are able to identify and avoid diaspores predated by insects. For H. alchorneoides, the proportion of diaspores with marks of frugivory only was lower than the proportion of diaspores lacking predation marks, probably due to the very small size of seeds. This indicates that frugivores consume more diaspores lacking predation marks because they are more abundant than diaspores with marks of predation. This study shows the influence of diaspore availability and of granivores in the consumption pattern of diaspores by frugivores.