Ecology Letters (2012) 15: 436–443
Understanding effects of species loss in complex food webs with multiple trophic levels is complicated by the idiosyncrasy of the predator effects on lower trophic levels: direct and indirect effects intermingle and may increase, decrease or not affect ecosystem functioning. We introduce a reductionist approach explaining a predator’s trophic effect only by empirically well-founded body-mass constraints on abundance, diet breadth and feeding strength. We demonstrate that this mechanistic concept successfully explains the positive, negative and neutral net effects of predators on decomposers in a litter microcosm experiment. This approach offers a new perspective on the interplay of complex interactions within food webs and is easily extendable to include phylogenetic and other body-mass independent traits. We anticipate that allometry will substantially improve our understanding of idiosyncratic predator effects in experiments and the consequences of predator loss in natural ecosystems.
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