Abstract
Summary Predation theory and empirical evidence suggest that top predators benefit the survival of resource prey through the suppression of mesopredators. However, whether such behavioural suppression can also affect the physiology of resource prey has yet to be examined.Using a three‐tier reef fish food web and intermittent‐flow respirometry, our study examined changes in the metabolic rate of resource prey exposed to combinations of mesopredator and top predator cues.Under experimental conditions, the mesopredator (dottyback, Pseudochromis fuscus) continuously foraged and attacked resource prey (juveniles of the damselfish Pomacentrus amboinensis) triggering an increase in prey O2 uptake by 38 ± 12·9% (mean ± SE). The visual stimulus of a top predator (coral trout, Plectropomus leopardus) restricted the foraging activity of the mesopredator, indirectly allowing resource prey to minimize stress and maintain routine O2 uptake. Although not as strong as the effect of the top predator, the sight of a large non‐predator species (thicklip wrasse, Hemigymnus melapterus) also reduced the impact of the mesopredator on prey metabolic rate.We conclude that lower trophic‐level species can benefit physiologically from the presence of top predators through the behavioural suppression that top predators impose on mesopredators. By minimizing the energy spent on mesopredator avoidance and the associated stress response to mesopredator attacks, prey may be able to invest more energy in foraging and growth, highlighting the importance of the indirect, non‐consumptive effects of top predators in marine food webs.
Highlights
Top predators can drive food web dynamics through a variety of direct and indirect effects (Abrams 1995)
Using a three-tier reef fish food web and intermittent-flow respirometry, our study examined changes in the metabolic rate of resource prey exposed to combinations of mesopredator and top predator cues
A general linear model (GLM) was used to examine the relationship between the change in activity (D line crosses) and the change in oxygen uptake (D O2 uptake; mg hÀ1) of damselfish juveniles exposed to the six treatments
Summary
Top predators can drive food web dynamics through a variety of direct and indirect effects (Abrams 1995). Trade-offs between predator avoidance and self-maintenance activities (reviewed by Lima 1998; Brown & Kotler 2004), top predators could have positive indirect effects on the lifetime fitness of resource prey (e.g. mating success, fecundity, reproductive rate). This can only be determined by detailed examinations of the effects of risk-induced trophic cascades on different behavioural, physiological and morphological traits of prey. Given that the anti-predator response of animals is proportional to the level of predation risk (Helfman 1989), we hypothesize that any restrictions in the activity and foraging of the mesopredator should reduce predator-induced stress and energy expenditure of the prey
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