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  1. Abstract

    Invasive predators can cause substantial evolutionary change in native prey populations. Although invasions by predators typically occur over large scales, their distributions are usually characterized by substantial spatiotemporal heterogeneity that can lead to patchiness in the response of native prey species. Our ability to understand how local variation shapes patterns of inducible defense expression has thus far been limited by insufficient replication of populations within regions. Here, we examined local and regional variation in the inducible defenses of 12 native marine snail (Littorina obtusata) populations within two geographic regions in the Gulf of Maine that are characterized by vastly different contact histories with the invasive predatory green crab (Carcinus maenas). When exposed in the field to waterborne risk cues from the green crab for 90 days, snails expressed plastic increases in shell thickness that reduced their vulnerability to this shell‐crushing predator. Despite significant differences in contact history with this invasive predator, snail populations from both regions produced similar levels of shell thickness and shell thickness plasticity in response to risk cues. Such phenotypic similarity emerged even though there were substantial geographic differences in the shell thickness of juvenile snails at the beginning of the experiment, and we suggest that it may reflect the effects of warming ocean temperatures and countergradient variation. Consistent with plasticity theory, a trend in our results suggests that southern snail populations, which have a longer contact history with the green crab, paid less in the form of reduced tissue mass for thicker shells than northern populations.

     
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  2. Coulson, Tim (Ed.)
  3. Abstract

    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 snailNucella 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 freePlain Language Summarycan be found within the Supporting Information of this article.

     
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