Prey vulnerability and predation pressure shape predator-induced changes in O2 consumption and antipredator behaviour

Predators regulate prey abundance (direct predation) as well as influencing their metabolism and behaviour (indirect effects) through the perception of risk. Antipredator traits are informed by individual experience of risk, which may vary over environmental gradients and through ontogeny. As prey grow, individual vulnerability generally diminishes, and the reduction in individual vulnerability with onto genetic growth can potentially lead to size refugia, ultimately nullifying the impacts of direct predation. Despite the ecological importance of the indirect effects of predation and the disproportionate influence larger individuals have on ecological level processes, there has been little focus on the potential indirect effects of predation risk on invulnerable prey. Using a combination of field and laboratory experiments, we measured the changes in routine oxygen consumption of vulnerable and invulnerable size classes of the intertidal snail Nucella lapillus (dogwhelk), exposed to effluent from its crab predator Carcinus maenas. To test the potential influence of prior experience of predation risk, measurements were conducted on populations naturally exposed to different levels of predation pressure. Field results showed that only invulnerable snails modified their routine oxygen consumption in the presence of risk, and this occurred across all populations. Oxygen consumption rates in the laboratory, however, contradicted the pattern, with only vulnerable prey responding to the perception of risk. Metabolic responses of both vulnerable and invulnerable prey under field and laboratory conditions are discussed in the context of asset protection and prey energetic state. Observations of snail behaviour in the laboratory showed that dogwhelks from exposed shores, where predatory risk is higher, were more likely to exhibit antipredator behaviour. Importantly, our findings provide evidence that the indirect effects of predators remain influential even after prey are no longer susceptible to direct predation and add to the growing body of evidence highlighting the ecological importance of indirect predation. (c) 2020 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.