Predators are known to have strong effects on their prey through both direct consumption of prey and through non-consumptive processes. When exposed to long periods of risk, prey often reduce their foraging rates. However, predators are mobile and create intermittent periods of relative safety and risk. When risky periods are long, they may be more impactful than multiple short periods of risk even if the total amount of time is equivalent. Previous studies of intermittent risky period focus on how these periods alter the behavior of a focal prey species, but our knowledge of how these periods influence prey growth and resource consumption is limited. To address this data gap, we developed a model of prey foraging and growth rates under temporal variability. We tested this model using a laboratory experiment of a tritrophic marine system. Our experiment investigated how a marine snail’s (Nucella ostrina) foraging rate on barnacles (Balanus glandula) changes in response to crab predators (Cancer productus). Over 8 weeks, snails were exposed to predators for 100% of the time, 50% of the time or 0% of the time. We used two 50% treatments and exposed snails to predators either every other week, or for 4 weeks in a row. We measured how many barnacles were eaten each week as well as the cumulative number of barnacles eaten over 8 weeks.
Results/Conclusions
Our model indicated that snails would reduce growth and foraging rates during longer periods of risk relative to shorter periods of risk. The weekly measurements of barnacle consumption indicate that snails respond quickly to predator presence and that response is consistent across all treatments. However, our experiment differed substantially from our predictions in that we found that short, frequent periods of risk caused significantly reduced cumulative numbers of barnacles eaten relative to the other treatments. This indicates that when exposed to high frequencies of risk, snails eat less during the safe periods as well as the risky periods. Therefore, the distribution of predation risk through time has a greater impact on prey foraging than we would expect. Our evidence shows that memory of previous risk is an important component in understanding how temporal variation influences trophic cascades.