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How Shell Morphology Mediates Patch Use in Response to Predation Risk in Freshwater Snails

Stevison, Blake K.
I examined how shell morphological defenses in freshwater snails (Physa sp.) influence patch choice and patch-use in response to predator cues. Behavioral responses were analyzed using a model comparison approach based on Akaike Information Criterion (AIC) to understand what morphological relationships and their interactions with predator cues best explained patch-use of the snails. I then tested alternative adaptive explanations for the morphological traits explaining patch-use by testing their effect on being killed by a predator in a no-choice predation study, as well as examining their influence on shell crush resistance. In this paper I also examined if the same type of cospecialization of complementary morphology and behavior found in earlier experiments occur between a behavior reducing the predator encounter rate, and morphological traits reducing the probability of surviving encounters with predators. I examined how shell morphology influences how physid snails use patches in the absence and presence of predator cues. I found that individuals with larger aperture lengths were more vulnerable to predators, and that more morphologically vulnerable individuals exhibited stronger antipredator behavior. Therefore, there is a compensatory relationship with an antipredator behavior and morphological defense that address different components of predation risk (i.e. reducing encounters with predators vs. increasing the probability of surviving such an encounter). I argue that separating predation risk into the two separate components of avoiding encounters and surviving encounters, can result in a better understanding of individual variation, and animal personalities in the context of predation risk.