Monday, August 6, 2007

PS 2-25: Heterospecific carnivory and cannibalism among tadpoles living in ephemeral pools in tropical pastures

Tanya J. Hawley, University of Miami

The role of tadpoles in aquatic systems is gradually being redefined, with recognition of their importance as carnivores and scavengers rather than strict herbivores and detritivores.  In the neotropics, it is not well known whether anuran assemblages in certain habitats are particularly prone to cannibalism and carnivory and the factors that influence the frequency of these feeding modes are poorly understood.  I conducted three experiments to address the following questions: 1) How prevalent is carnivory among tadpoles found in ephemeral pasture pools?, 2) Is the frequency of cannibalism influenced by the size and developmental stage of predators and prey?, and 3) Do density, food availability, and relatedness influence the frequency of cannibalism and performance of tadpoles?  Field surveys and experimental manipulations were conducted in the Osa Peninsula, Costa Rica.  Facultative heterospecific carnivory and cannibalism are common foraging modes among species that reside in ephemeral pasture pools.  Cannibalism in Smilisca phaeota was dependent on the size and stage of predators and prey, with medium and large tadpoles causing almost complete mortality of eggs, but less mortality of mobile hatchlings.  In contrast, small tadpoles caused less mortality of prey at all developmental stages.  S. phaeota cannibalism occurred most often among tadpoles in treatments with low availability of vegetative food.  S. phaeota tadpole performance (survival, metamorph mass, and time to metamorphosis) was influenced by tadpole density and the amount of vegetative food; however, diet supplementation with conspecific eggs and tadpole relatedness had few effects on performance.  These results are consistent with previous work demonstrating the large role density and food limitation have on the frequency of tadpole cannibalism.  Further, the high number of species that exhibit tadpole carnivory in pastures suggests that this feeding mode may be advantageous to tadpoles in these ephemeral pools.