Demographic Responses in a Population of the Strawberry Poison Frog (Oophaga pumilio) after Resource Manipulations

Resource availability not only determines species assemblages but can also influence local density. The critical resource for a species or population is not always obvious. Among poison frogs (Dendrobatidae), whose populations are not limited by predation due to their toxicity, resource limitation may be key in determining density of a population. Strawberry Poison Frogs, Oophaga pumilio, are a small dendrobatid in Central America that exhibits parental care at specialized nest sites in rearing of offspring. Resources that may influence population density are varied, although nest sites with available food and ability to rear offspring are likely important factors. We sought to assess how population demographics changed with alterations to food and rearing sites in one population of O. pumilio on Isla Colon of Bocas del Toro, Panama. To test this hypothesis, we established 18 plots and made observations June-August 2009 and May-June 2010. We manipulated resources by the addition or removal of leaf litter and by providing artificial rearing sites. Artificial rearing sites were large diameter drinking straws folded in half to catch water, mimicking the water tanks found in bromeliads. Population density was not affected by manipulations of leaf litter, suggesting that food resources are not limiting to local density. However, artificial rearing sites were found to have a significant effect; on average, addition of artificial rearing sites resulted in doubling of the population. This study demonstrates that availability of offspring rearing sites is an important limiting resource for phytotelmata-breeding amphibians.