Tropical Tadpole Vulnerability to Predation: Association between Laboratory Results and Prey Distribution in an Amazonian Savanna

Abstract

We tested concordance between patterns of tadpole assemblage structure seen in the field and in laboratory experiments to infer causal relationships. Based on a previous study that showed predators as the main proximal factor associated with tadpole distributions in an Amazonian savanna, we investigated interspecific patterns of vulnerability of six common tadpole species in relation to the distribution of predators in the field. The predators used were hydrophilid larvae (Coleoptera), libellulid naiads (Odonata), and adult Geophagus gr. altifrons (Cichlidae). Forty riverside aquatic sites were searched for predators and tadpoles during 28 months in a savanna area at the border of the Tapaj6s River, Central Amazonia. Tadpole species were tested for their vulnerability to predators in individual and choice tests. Prey unpalatable to fishes (Bufo marinus, B. granulosus, and Hyla wavrini) were palatable to invertebrates. Leptodactylus macrosternum and Scinax rubra were vulnerable to fish and invertebrate predators. Lysapsus limellus was not tested with fish, but it was vulnerable to naiads. Eggs had low vulnerability to predation, but there was generally little ontogenetic change in tadpole vulnerability. The vulnerability of tadpoles in choice tests was significantly related to vulnerability in individual tests. A tadpole vulnerability index based on tadpole survivorship with different predators was significantly related to the distribution of predators in the field, indicating that it is possible to predict the coexistence of prey and predators in the field by screening species with simple laboratory predation experiments. In this study area, both vertebrate and invertebrate predators may potentially limit the distribution and the relative abundance of tadpole species through differential predation.