Does refuge availability alter the effect of predation risk on prey growth?

While being eaten by a predator has obvious costs for prey fitness, prey avoidance of predation risk can also incur substantial fitness costs through risk-induced changes in reproduction, growth and survival. Prey that respond to predation risk by utilizing refugia, for instance, may face a greater degree of within-refuge competition. We tested whether cricket (Acheta domesticus) responses to a predator (the Chinese mantid, Tenodera sinensis) are altered by the presence of refuges by conducting a 2*2 factorial experiment where the presence/absence of a predator was crossed with the presence/absence of a prey refuge. Each treatment was replicated ten times; ten crickets were placed in each replicate enclosure, and one mantid in each predator-present replicates. To protect against direct predator mortality, the mantids did not have access to the crickets. The crickets in each replicate were weighed before the experiment started, and after one week. We found that predation risk did not affect prey growth. When predators were absent, however, prey with access to a refuge grew more than prey without a refuge (p<0.05). On the basis of these results, we conducted another experiment examining specifically how refuge presence/absence affects prey growth. Because this experiment was specifically interested in the impact of refuges, it did not include a predation risk treatment. The second experiment had 20 replicates per treatment, with ten crickets per replicate, and lasted one week. Despite the results of the first experiment, there was no difference in cricket growth between the refuge and no-refuge treatments.