The ecology of larval Hyla andersonii (Anura: Hyladae): The effects of predation by aquatic insects, competition with larval anurans andpH

Larval anuran distributions are limited by both biotic and abiotic factors. I performed field surveys to identify biotic and abiotic factors that potentially limit the distribution of larval Hyla andersonii. These surveys revealed an association of larval H. andersonii with low pH ponds and documented high densities of potential predators and competitors in natural ponds. A series of natural and artificial pond experiments tested whether H. andersonii larvae are directly affected by pH, predation by aquatic insects, or competition with other species of larval anurans. These experiments further tested whether pH altered the outcome of interspecific interactions. H andersonii larvae were not affected by pH, but suffered greatly from predation by aquatic insects and competition with two species of larval anurans, Rana sphenocephala and Hyla versicolor. Contrary to expectation, competition with H. versicolor, a closely-related, allotopic species, had less of an effect on H. andersonii tadpoles than did competition with R. sphenocephala, a more distantly-related, co-occurring species. Low pH did not alter the outcome of any interspecific or intraspecific interactions. In this system biotic interactions had stronger effects than abiotic factors. My findings also caution against the use of patterns detected in nature to predict causation. Although larval H. andersonii are found mostly in acidic ponds, pH had no effects in artificial pond experiments. In addition, degree of relatedness and/or co-occurrence were not good predictors of strength of competition among larval anurans.