The interaction between predation and competition

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Competition and predation are the most heavily investigated species interactions in ecology, dominating studies of species diversity maintenance. However, these two interactions are most commonly viewed highly asymmetrically. Competition for resources is seen as the primary interaction limiting diversity, with predation modifying what competition does1, although theoretical models have long supported diverse views1,2,3,4,5. Here we show, using a comprehensive three-trophic-level model, that competition and predation should be viewed symmetrically: these two interactions are equally able to either limit or promote diversity. Diversity maintenance requires within-species density feedback loops to be stronger than between-species feedback loops. We quantify the contributions of predation and competition to these loops in a simple, interpretable form, showing their equivalent potential to strengthen or weaken diversity maintenance. Moreover, we show that competition and predation can undermine each other, with the tendency of the stronger interaction to promote or limit diversity prevailing. The past failure to appreciate the symmetrical effects and interactions of competition and predation has unduly restricted diversity maintenance studies. A multitrophic perspective should be adopted to examine a greater variety of possible effects of predation than generally considered in the past. Conservation and management strategies need to be much more concerned with the implications of changes in the strengths of trophic interactions.

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Figure 1: Simplified three-trophic-level food web.
Figure 2: Coexistence and exclusion regions.
Figure 3: Niches of two focal species in terms of resources and predators.
Figure 4: Niche overlap as a function of relative predation intensity.


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This work was supported by National Science Foundation grants DEB-0542991 and DEB-0717222.

Author Contributions P.C. and J.J.K. jointly developed the model. P.C. derived the coexistence conditions and wrote the first draft of the manuscript. P.C. and J.J.K. jointly prepared the figures and all revisions of the manuscript.

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Correspondence to Peter Chesson or Jessica J. Kuang.

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Chesson, P., Kuang, J. The interaction between predation and competition. Nature 456, 235–238 (2008) doi:10.1038/nature07248

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