The Effect of Ontogeny on Interspecific Interactions in Larval Amphibians

Abstract

We used 3 x 2 x 2 factorial experiments in a temporary pond to assess the relative importance of predator density (0, 2, or 4 salamander larvae), prey density (20 or 40 tadpoles), and time of prey introduction (early or late) on interactions between predaceous larval salamanders (Ambystoma tigrinum) and their anuran prey (Pseudacris triseriata). We examined how these factors and their interactions affected mass at metamorphosis, length of larval period, growth rate, and survival. These experiments demonstrated the effect of body size on predator—prey interactions by manipulating time of introduction of size—structured prey in a system with a gape—limited predator. Microhabitat differences in primary productivity, sources of predation other than salamanders, and abiotic factors were important determinants of community structure. High levels of salamander predation negatively affected tadpole survival, but affected no other response variable. We detected no density—dependent effects in either taxon. Tadpoles in the early treatment had longer larval periods and lower survival rates than those in the late treatment. Interactions of factors, including time of introduction, were common. Biotic and abiotic factors differentially affecting growth of predator or prey appear to be responsible for these differences. Priority effects in arrival to breeding sites, or climatic events affecting the growth rate of predator, prey, or both, play a role in determining community structure. Interactions of factors complicate the predator—prey relationship. In our experiment, the effects of time of introduction are highly correlated with body size in the two temporal treatments. Our results indicate that more realistic models of predator—prey systems, or population dynamics, should incorporate size structure of predator and prey.