The right choice: predation pressure drives shell selection decisions in the hermit crab Calcinus californiensis

Abstract

Several prey species use refuges to avoid predation. Prey need to abandon and shift between refuges. However, during such shifting, prey can be vulnerable to predators. We hypothesize that predator presence may induce prey to make mistakes in choosing their refuge. We tested this by inducing the hermit crab Calcinus californiensis Bouvier, 1898 to shift to a new empty gastropod shell (three different species: Columbella Lamarck, 1799, Nerita scabricosta Lamarck, 1822, and Stramonita biserialis (Blainville, 1832)) in the absence and presence of Eriphia squamata Stimpson, 1860, which is an efficient shell-crushing natural crab predator. We expected that when a predator was present, hermit crabs would (i) inspect fewer shells and (or) (ii) change to a shell that is either too heavy to allow escape or unfit in size to accommodate the hermit crab. Although the first prediction was met, the second prediction was supported only when S. biserialis shells were used. Thus, in the presence of a predator, hermit crabs prioritize escaping by selecting lighter shells, which would allow the crab to move faster. We conclude that predator presence may induce prey to make mistakes in refuge selection, suggesting that this has severe consequences in future predatory events.