Ecology and evolution of foraging behavior in cannibalistic populations

In many cannibalistic populations, opportunities for growth and mortality risk associated with activity depend on body size, because cannibals generally eat only smaller prey. Foraging decisions balance these risks and benefits and determine changes in size structure through variation in individual growth and mortality. Therefore, there is a dynamic association between individual foraging behavior and size structure; foraging behavior both determines, and is modified by, size structure. Understanding how this interdependence functions is critical for studying the evolution of behavior in an ecological context.; This study addresses the relationship between foraging behavior and size structure in single-aged cohorts of Arizona tiger salamander larvae, Ambystoma tigrinum nebulosum. In a series of laboratory experiments, it was shown that size differences among tiger salamander larvae emerge due to size-specific interactions. Smaller salamander larvae reduced feeding rates in the presence of larger larvae, even when isolated from larger individuals during feeding. There was an inverse relationship between feeding rate and the size of neighboring larvae. These results indicate salamander larvae respond to risk of cannibalism by reducing foraging activity, leading to increased size variation. A model was developed: (1) to analyze interactions between foraging behavior and size structure development, and (2) to make predictions concerning optimal responses to cannibalism. The model showed significant effects of size structure development on optimal foraging behavior and suggested foraging under the risk of cannibalism can have many effects on size structure depending on the ability of individual larvae to assess risk. A field experiment and survey were conducted to determine effects of ontogenetic diet shifts on size structure development. The field experiment showed switching to large insect prey can increase size variation by increasing growth of larger individuals. This effect was not detected in the survey due to the presence of confounding factors most notably the direct mortality effects of cannibalism.; These studies show that foraging behavior and size structure development are tightly linked in populations of Arizona tiger salamanders. Models of phenotypic evolution should include such interactions among phenotypes given their prevalence in natural populations.