Predation as the key factor structuring tadpole assemblages in a savanna area in Central Amazonia

Abstract

We investigated the role of predation and abiotic factors in determining tadpole species distribution and assemblage structure in a savanna area in Central Amazonia, Brazil. We sampled 40 aquatic sites monthly during 2.5 years for tadpoles, predators, and physiochemical characteristics. Most tadpole species showed temporal overlap but spatial segregation and low density, suggesting that interspecific competition among tadpoles is not presently important in this system. Invertebrate predators coexisted with more tadpole species than did fishes, suggesting that predation by fishes strongly influences the composition of tadpole assemblages. Ordination techniques were used to reduce dimensionality to simple vectors, which were then used in multiple regression analyses to search for key factors associated with tadpole assemblage structure. Although species composition was not directly related to abiotic characteristics, path analysis showed that the size and degree of permanence of the water body may indirectly influence species composition by altering predator composition. Tadpole species richness in a water body was not significantly related to abiotic factors or predators. However, predators were the main factor influencing tadpole assemblage composition. Most previous studies on tadpole community dynamics suggested that predators affect alpha (within habitat) diversity, but they did not consider beta diversity (among habitats). Our results showed that predators influenced beta diversity but had little or no effect on variation in alpha diversity.