Abstract
Although the cascading impact of predators depends critically on the relative role of lethal predation and predation risk, we lack an understanding of how human-caused stressors may shift this balance. Emergent evidence suggests that pollution may increase the importance of predator consumptive effects by weakening the effects of fear perceived by prey. However, this oversimplification ignores the possibility that pollution may also alter predator consumptive effects. In particular, contaminants may impair the consumptive effects of predators by altering density-dependent interactions among prey conspecifics. No study has directly compared predator consumptive and non-consumptive effects in polluted versus non-polluted settings. We addressed this issue by using laboratory mesocosms to examine the impact of sublethal doses of copper on tri-trophic interactions among estuarine predator crabs Cancer productus, carnivorous whelk prey Urosalpinx cinerea, and the basal resource barnacles Balanus glandula. We investigated crab consumptive effects (whelks culled without crab chemical cues), non-consumptive effects (whelks not culled with crab chemical cues), and total effects (whelks culled with crab chemical cues) on whelks in copper polluted and non-polluted waters. Realistic copper concentrations suppressed the effects of simulated crab lethal predation (whelk culling) by removing density-dependent feeding by whelks. Specifically, reductions in conspecific density occurring in elevated copper levels did not trigger the normal increase in whelk consumption rates of barnacles. Weakened effects of fear were only observed at extremely high copper levels, suggesting consumptive effects were more sensitive to pollution. Thus, pollution may shape communities by altering the roles of predators and interactions among prey.
Highlights
Predators strongly impact community structure and function through consumptive and non-consumptive effects on prey [1,2,3,4]
Whelks foraging alone had twice the per capita consumption rates of whelks foraging in groups of 10 (Fig 1)
Whelks exposed to predation risk ate consistently across copper levels (ANOVA, F1,23 = 0.88, p = 0.36; linear regression, R2 = 0.78, p = 0.191, Fig 2)
Summary
Predators strongly impact community structure and function through consumptive (eating) and non-consumptive effects (scaring) on prey [1,2,3,4] The balance of these effects can influence. The energy and nutrients from prey are transferred to higher trophic levels. This transfer is impaired as non-consumptive effects become increasingly important. Anthropogenic stressors such as climate change [7], overfishing [8], invasive species [9], and pollution [10] can influence predator-prey interactions, stressor impacts on the balance of these effects is poorly known
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