The hermit crab Pagurus acadianus (Benedict) possesses two major defences against mobile aquatic predators, viz., fleeing and refuging in its gastropod shell. When approached by a potential predator, a crab must choose to either continue its current activity (e.g., feeding), flee or hide in its shell. If a foraging crab flees when threatened, it must secondarily decide whether to carry its food item and, if so, how far to carry it whilst escaping. Alternatively, if the crab takes refuge in its shell, it must then decide how long to remain hidden and when to resume locomotory activity following emergence from the shell. Because these behavioural alternatives have associated costs (e.g., energy expenditure, predation risk, lost foraging opportunity), the crabs' decision as to which behaviour to adopt should be sensitive to the respective cost of each. We tested specific predictions of this general economic hypothesis of behavioural decision making by varying the weight of food items presented to crabs (= lost feeding opportunity cost, energetic cost of carry) and the amount of time the crabs were "handled" by a predator following "capture" (= predation risk). Most crabs tested fled from an approaching lobster predator model. Contrary to expectation, flight initiation distance was unaffected by the mass of the food item available to the foraging crabs. As predicted, however, the distances fleeing crabs carried individual food items varied inversely with the food's weight. Time spent hiding in the shell and latency to resume locomotion following a predator "attack" were relatively unaffected by the size of the food item available. As expected, the crabs' decision to emerge from their shell following a threat appeared sensitive to their perceived risk of predation, as evidence by an observed positive relationship between refuging time (in shell) and the duration of preceding handling of the crab by the predator. These findings are interpreted within the cost-benefit framework of behavioural decision making.

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Keywords Antipredation, Crab, Decision making, Foraging, Predation risk, Trade-off
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Journal Journal of Experimental Marine Biology and Ecology
Scarratt, A.M. (Alison M.), & Godin, J.-G.J. (1992). Foraging and antipredator decisions in the hermit crab Pagurus acadianus (Benedict). Journal of Experimental Marine Biology and Ecology, 156(2), 225–238. doi:10.1016/0022-0981(92)90248-9