Intrinsic factors affecting predator failure in crab-gastropod encounters and their implications for repair scar frequencies

Abstract

Repair scars result from sublethal predator damage which is regrown, permanently recording predator-prey encounters. Although interactions between crabs and gastropods are well studied, it is not clear under what conditions these encounters lead to the generation of repair scars. As failed attacks generate repair scars, here, we use arena experiments to investigate intrinsic factors affecting the likelihood of predator failure using the crab, Cancer productus, and two of its common gastropod prey, Nucella ostrina and Tegula funebralis. Regression models indicate that C. productus was 44 % more likely to fail in encounters with T. funebralis than those with N. ostrina, which may be due to differences in shell strength and shape. In addition, encounters with T. funebralis were much longer in duration than those with N. ostrina, particularly for large prey attacked by small predators. Predator size had a direct effect on attack outcomes, particularly for T. funebralis, and the long duration of encounters suggests that in natural settings, extrinsic factors could potentially have large effects on failure rates. Field data show that T. funebralis populations tend to have greater repair frequencies than do coexisting N. ostrina. We propose that differences in repair frequency between T. funebralis and N. ostrina at the same location are likely due to intrinsic factors. However, repair scar frequencies may also reflect the density of small predators, as repair scars may primarily result from small crabs, which are also more likely to be interrupted by extrinsic factors in natural settings.