Seasonal Patterns of Intraguild Predation and Size Variation among Larval Salamanders in Ephemeral Ponds

Predation among potential competitors, or intraguild predation (IGP), is dependent on size disparities between competing predators and prey and strongly influences the ecology of larval amphibians in ephemeral ponds. Although intraguild prey are hypothesized to exhibit faster growth rates than intraguild predators and, therefore, outgrow predation risk through time, intraguild predation also is associated with significant increases in predator growth rates that are hypothesized to increase the potential for future predation. Given these conflicting hypotheses, how predation among amphibian larvae early in development should influence size disparities and ontogenetic shifts in predation risk is unclear. To clarify the effects of intraguild predation on predator and prey growth, we quantified size variation among larval salamanders (Ambystomatidae) in forested ephemeral ponds while concurrently monitoring seasonal patterns of intraguild predation through gut content analyses. Intraguild predation had no discernible effect on either interspecific size disparities between intraguild predators and prey, or intraspecific size variation within predator populations, and factors of larval density, tadpole density, and pond area were more important than larval size variation in predicting IGP. Our results do not support previous assertions regarding the consequences of intraguild predation for predator-prey size disparities, because top predators not actively engaging in IGP appeared to maintain growth rates equivalent to successful conspecific IG predators, and the frequency of intraguild predation did not significantly change during larval ontogeny. The lack of consistent increases or decreases in predator-prey size disparities suggests that intraguild prey may not experience predictable ontogenetic shifts in intraguild predation risk.