Ants, rodents and seed predation in Proteaceae

Abstract

Many species of Cape Proteaceae have seeds dispersed by ants. Ants may reduce seed prédation by rapidly transporting and burying seeds in their nests. Three field experiments using ant and vertebrate exclosures were set up to determine whether prédation of Mimetes pauciflorus and Leucospermum glabrum fruits is significant, whether ants reduce it, and whether the food body (elaiosome) is important in the interaction. Results showed that seed prédation could be as high as 100%, but that ants usually discover and remove seeds before vertebrates. Significantly fewer seeds were dispersed by ants when elaiosomes were removed. Vertebrate removal rates also declined. Laboratory experiments with caged small mammals showed that intact seeds were found more readily than seeds from which elaiosomes had been removed and that seed discovery improved with experience. Different species varied in their ability to detect seeds. Our results suggest that seed dispersal by ants has a direct effect on the number of seeds entering the soil seed bank by reducing prédation, that myrmecochorous seeds produce a signal which attracts both ants and small mammals, and that once seeds are buried in ant nests predation is probably minimal.