Sex-specific differences in the response of prey to predation risk

The non-consumptive effects of predation risk can strongly affect prey behaviour and fitness with emergent effects on community structure and ecosystem functioning. Prey may respond differently to predation risk based on key traits such as sex, but the influence of sex-specific variation is typically explored in species with strong sexual dimorphism. However, sex-specific responses to predation risk may arise even in prey species lacking sexual dimorphisms based on differences in the relative cost of reproduction. Using a rocky intertidal food chain, we conducted a laboratory mesocosm experiment to explore sex-specific responses of morphologically similar, reproductively mature prey (the snail Nucella lapillus) to predation risk and whether risk affected female fecundity. We found that predation risk suppressed prey growth only in males via effects on growth efficiency, suggesting that sex-specific disparities may arise due to differences in the energy required for reproduction and/or the costs of mounting a physiological stress response. Moreover, while risk did not affect overall female fecundity, it eliminated the positive relationship between female size and fecundity observed in the absence of risk. We hypothesize that these sex-specific disparities arise due to differences in the energy required for reproduction and/or the costs of mounting a physiological stress response. Reproduction is likely more energetically costly for females than males, so females may display weaker antipredator responses in order to maintain energetic reserves needed for reproduction. Our results suggest that sex-specific responses may be an important component of inter-individual differences in prey responses to risk and influence prey population growth and demography even in species lacking sexual dimorphism. A free Plain Language Summary can be found within the Supporting Information of this article.