Temperature affects susceptibility of intertidal limpets to bird predation

Abstract

High temperatures resulting in physiological stress and the reduced ability to resist predation can have life-or-death consequences for an organism. We investigated the effects of temperature on the susceptibility to predation for an ectothermic intertidal mollusc (the owl limpet, Lottia gigantea Sowerby) and its predator, the black oystercatcher (Haematopus bachmani Audubon). The ability of L. gigantea to resist bird predation during low tide is determined by the tenacity of attachment to the rock. We developed a transducer to measure the force of predatory attacks on limpets by a captive black oystercatcher and tested the hypothesis that exposure to warm temperatures during low tide emersion would affect the limpet's ability to resist dislodgement in trials with a morphometrically accurate beak mimic and a live bird. In beak mimic trials, four times as many limpets exposed to warm low tides were removed, as compared to limpets exposed to cool low tides or in ‘no low tide’ submerged conditions. Minimum time before limpet removal in captive bird trials was more than six times longer for limpets in cool low tide or no low tide treatments compared to limpets in the warm low tide treatment. We measured shear forces up to 36.63 N during predatory strikes. These direct measurements of the forces exerted by a living oystercatcher provide context for interactions with multiple prey species. Our data suggest that naturally occurring variation in body temperatures among individual prey items in the field could be an important driver of predator-prey interactions and subsequently community patterns.