The hidden cost of safety: Prey refugia increase the negative effect of predation risk in aquatic systems

Background/Question/Methods: Refuge habitats, where organisms seek shelter from predators or harsh abiotic conditions, are among the most common components of habitats. By definition, prey in refuges experience the benefit of decreased consumption by predators. However, if predators cause prey to use refuge habitats, prey may experience detrimental, non-consumptive effects of predators due to increased competitive interactions in the refuge. Despite the widespread nature of refuges and the clear benefits of decreased consumption by predators, it is unknown whether predator-mediated use of refuge habitats has negative non-consumptive effects on prey growth, survival, and fecundity. We performed a meta-analysis of 204 studies of aquatic taxa containing data on 271 distinct predator-prey pairs.

Results/Conclusions: We found strong evidence that the effect of predation risk on prey growth, fecundity, and survival increases when prey have access to refuge habitats. These results suggest that prey trade off the potential costs of predation with the costs of competition, and that both carry a substantial cost. Moreover, our results reveal key pragmatic considerations for researchers studying non-consumptive effects: the magnitude and direction of non-consumptive effects clearly depends on the presence of refuge habitat and studies must be designed to accommodate the behavioral tradeoff of predation risk and starvation (as per the risk allocation hypothesis). By illustrating that predator-mediate used of refuge habitats has strong, negative non-consumptive effects on prey, our work provides a comprehensive perspective on the ecological costs and benefits of ubiquitous refuge habitats.