Morphological defense influences absolute, not relative, nonconsumptive effects in marine snails

Abstract

Theory predicts that the strength of nonconsumptive predator effects (NCEs) depends on the state of individual prey and their vulnerability to predators. This prediction has rarely been tested, particularly with respect to interspecific variation in the vulnerability of closely related (i.e., within the same genus) guild members within a community. I examined the relationship between morphological vulnerability and predator-induced feeding suppression among 3 species of predatory whelks (Nucella spp.) that differ in their morphological defense—shell armor. Weaker-shelled species (N. ostrina and N. canaliculata) were more vulnerable to predation by crabs (Cancer productus) than the stronger-shelled species (N. lamellosa). Crab cues suppressed feeding in the most vulnerable species to a greater extent than the 2 less vulnerable species in absolute terms, but proportional decreases in feeding due to crab cues were no different among species. Thus, species-specific differences in feeding activity are maintained in the presence of crab cues, suggesting that the degree to which congeneric guild members transmit NCEs is related to constitutive levels of feeding activity rather than morphological defense. These results contrast with the commonly observed pattern of behavioral compensation for weaker morphological defenses in distantly related gastropod species and highlight the importance of examining the absolute and proportional predator-induced changes in behavior of different prey species. Key wor ds: antipredator behavior , food web, gastropod, nonconsumptive effect, trait compensation, trophic cascade. [Behav Ecol]