Many prey species use refuge habitats to reduce their risk of predation. The safety provided by refuges is typically traded for reduced foraging opportunities by prey, which may emerge because 1) resource competition can be particularly intense within refuges and 2) the quality of resources within a refuge may be low compared to riskier habitats. Hence, refuge use can escalate the costs of risk and the strength of nonconsumptive effects on prey. Such costs, however, may be shaped by the variation in the quantity and quality of resources that refuges harbor for prey foraging (i.e., refuge quality). Despite its potential importance, we lack an explicit understanding of how refuge quality impacts prey performance under risk. Moreover, it has been difficult to precisely evaluate the cost of refuges because their costs and benefits are often confounded, such as when shifts into refuge necessitate changes in prey diet. Using a well-studied intertidal system, we examined how predation risk (from the green crab, Carcinus maenas) and refuge quality (amount of resources, the barnacle Semibalanus balanoides, available in refuge) interact to influence the risk-taking behavior, foraging, and performance of prey, the carnivorous snail Nucella lapillus.
Results/Conclusions
We found that high quality refuges with more resources greatly reduced the costs of refuge use to prey: nonconsumptive effects were substantially weaker, with especially strong impacts on growth and growth efficiency. In the presence of predation risk, prey spent more time in high quality refuges, allowing them to forage and grow more. Remarkably, we also found that higher quality refuges substantially improved prey growth efficiency (ability to convert ingested energy into body mass) in the presence, but not absence of risk, suggesting that refuge quality mitigates prey stress levels associated with increased risk. In addition, the effects of refuge quality on prey behavior, growth, and growth efficiency were nonlinear, revealing that even modest increases in refuge quality can substantially weaken the costs of risk. Our results highlight refuge quality as a central factor influencing prey responses to predation risk and suggest that a more nuanced attention to refuge quality will provide better insight into how risk influences organismal performance and the structure and function of natural communities. Failure to consider refuge quality will likely lead to overestimates of the costs associated with prey refuge use.