Predation can have strong effects on the structure of pond-breeding amphibian communities. Many factors can influence the outcome of predator–prey interactions, including differences in densities, identities, and body sizes of both predator and prey. These different mediating factors can impart synergistic impacts on predation rates, though distinguishing such interactions among multiple factors are underexplored. We examined whether different body sizes of two predators, larval Marbled Salamanders (Ambystoma opacum) and adult Lesser Sirens (Siren intermedia), varied in their ability to forage on larval anurans across a range of prey densities. We specifically tested whether attack rates and handling times, the two main parameters of functional response models, varied across three size classes in both predator species. We found that larval Marbled Salamanders exhibited a Type II (saturating) functional response and that larger individuals had higher attack rates and shorter handling times, resulting in greater prey mortality at higher prey densities with larger predators. In contrast, Lesser Sirens were largely ineffective predators despite being an order of magnitude larger in body size than Marbled Salamanders; tadpole mortality was largely unrelated to their own density. Predator body size was a significant predictor of prey mortality for both predator species. Overall, our study shows that species identity could be as important as predator body size when predicting the outcomes of predator–prey interactions.
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Vol. 108 • No. 2