O'Gorman and Emmerson 2009

O'Gorman and - Perturbations to trophic interactions and the stability of complex food webs Eoin J O’Gorman 1,2 and Mark C Emmerson 2

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Unformatted text preview: Perturbations to trophic interactions and the stability of complex food webs Eoin J. O’Gorman 1,2 and Mark C. Emmerson 2 Environmental Research Institute, University College Cork, Lee Road, Cork, Ireland; and Department of Zoology, Ecology and Plant Sciences, University College Cork, Distillery Fields, North Mall, Cork, Ireland Edited by Robert T. Paine, University of Washington, Seattle, WA, and approved July 2, 2009 (received for review April 6, 2009) The pattern of predator–prey interactions is thought to be a key determinant of ecosystem processes and stability. Complex eco- logical networks are characterized by distributions of interaction strengths that are highly skewed, with many weak and few strong interactors present. Theory suggests that this pattern promotes stability as weak interactors dampen the destabilizing potential of strong interactors. Here, we present an experimental test of this hypothesis and provide empirical evidence that the loss of weak interactors can destabilize communities in nature. We ranked 10 marine consumer species by the strength of their trophic interac- tions. We removed the strongest and weakest of these interactors from experimental food webs containing > 100 species. Extinction of strong interactors produced a dramatic trophic cascade and reduced the temporal stability of key ecosystem process rates, community diversity and resistance to changes in community composition. Loss of weak interactors also proved damaging for our experimental ecosystems, leading to reductions in the tempo- ral and spatial stability of ecosystem process rates, community diversity, and resistance. These results highlight the importance of conserving species to maintain the stabilizing pattern of trophic interactions in nature, even if they are perceived to have weak effects in the system. biodiversity and ecosystem functioning u dynamic index u interaction strength u predator–prey interactions u temporal and spatial variability F or decades, scientists have argued over the natural phenom- ena that allow complex communities to persist in nature (1–3). Randomly assembled communities become less stable with increasing complexity (2, 4), but natural communities are finely structured (5, 6), displaying properties that promote stability despite complexity (7). Experiments (8–10) and theory based on empirical data (11, 12) have shown that real food webs are characterized by few strong interactions embedded in a majority of weak links. It is thought that this nonrandom arrangement of interaction strengths promotes community-level stability by generating negative covariances, which suppress the destabilizing effect of strong consumer-resource interactions (3)....
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O'Gorman and - Perturbations to trophic interactions and the stability of complex food webs Eoin J O’Gorman 1,2 and Mark C Emmerson 2

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