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Trophic cascades: the primacy of trait-mediated indirect interactions
Authors:Oswald J Schmitz  Vlastimil Krivan  Ofer Ovadia
Institution:School of Forestry and Environmental Studies, Yale University, New Haven, CT, USA; Department of Ecology and Evolutionary Biology, Yale University, 370 Prospect Street, New Haven, CT 06511, USA; Department of Theoretical Biology, Institute of Entomology Brani?ovská31, 370 05 ?eské, Budějovice, Czech Republic
Abstract:Trophic cascades are textbook examples of predator indirect effects on ecological systems. Yet there is considerable debate about their nature, strength and overall importance. This debate stems in part from continued uncertainty about the ultimate mechanisms driving cascading effects. We present a synthesis of empirical evidence in support of one possible ultimate mechanism: the foraging‐predation risk trade‐offs undertaken by intermediary species. We show that simple trade‐off behaviour can lead to both positive and negative indirect effects of predators on plant resources and hence can explain considerable contingency on the nature and strength of cascading effects among systems. Thus, predicting the sign and strength of indirect effect simply requires knowledge of habitat and resource use by prey with regard to predators’ presence, habitat use and hunting mode. The synthesis allows us to postulate a hypothesis for new conceptualization of trophic cascades which is to be viewed as an ultimate trade‐off between intervening species. In this context, different predators apply different rules of engagement based on their hunting mode and habitat use. These different rules then determine whether behavioural effects persist or attenuate at the level of the food chain.
Keywords:Adaptive foraging  anti-predator behaviour  cascading effects  density-mediated indirect effects  food chains  food web topology  predation risk-foraging trade-offs  predator identity  predator–prey interactions  trait-mediated indirect effects
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