Aquatic Predators and Tadpole Prey in Central Amazonia: Field Data and Experimental Manipulations

Abstract

Experimental manipulations of aquatic predators (odonate naiads and fishes) and prey (three tadpole species: Osteocephalus taurinus, Phyllomedusa tomopterna, and Epipedobates femoralis) investigated the role of predators in the organization of a tropical larval anuran assemblage. Eighteen months of surveys of 31 primary forest lentic sites examined phenological patterns of tadpole and predator species. I tested for a relation between predator and metamorph presence using the Mantel—Haenszel chi—square. I tested for differences in survival and development for each tadpole species as a function of predator identity. I examined correlations between growth of surviving tadpoles and both the number of conspecific and the total number of surviving tadpoles. Two—way ANOVAs tested for differences in predation rate among predators and experiments. Finally, I tested for differences in selectivity for each prey species. Odonate naiads were the most common predator in upland isolated pools and peccary wallows, while fish were most common in lowland, stream—associated habitats. No relation was found between the presence of metamorphs and of predators in natural sites, except for metamorph presence (a positive relation for all tadpole species pooled) and presence of aeshnid larvae in natural sites. Predators reduced tadpole survival in three of four different prey—species combinations. Aeshnid naiads were the most effective predators, followed by libellulid naiads. Fish were never the most effective predators and their effect was variable. Predation rate on each of the three prey species varied among predators and sometimes depended upon which species were present, indicating that predation rate in the system was a function of the particular combination of prey species. No significant differences were found in selectivity for any prey species among individual predator types. All predators, however, preferred P. tomopterna, the less abundant species, over O. taurinus whenever the two species were together. Growth of tadpoles was inversely related to the number of surviving conspecific tadpoles. Predators, therefore, have the potential to modify the composition of tadpole species assemblages through differential predation.