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Weak trophic interactions and the balance of nature

Abstract

Ecological models show that complexity usually destabilizes food webs1,2, predicting that food webs should not amass the large numbers of interacting species that are in fact found in nature3,4,5. Here, using nonlinear models, we study the influence of interaction strength (likelihood of consumption of one species by another) on food-web dynamics away from equilibrium. Consistent with previous suggestions1,6, our results show that weak to intermediate strength links are important in promoting community persistence and stability. Weak links act to dampen oscillations between consumers and resources. This tends to maintain population densities further away from zero, decreasing the statistical chance that a population will become extinct (lower population densities are more prone to such chances). Data on interaction strengths in natural food webs7,8,9,10,11 indicate that food-web interaction strengths are indeed characterized by many weak interactions and a few strong interactions.

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Figure 1
Figure 2: The local minima and maxima for top predator density, P, attained in the attracting solutions for a range of relative interaction strengths.

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Acknowledgements

We thank P. DeValpine, M. Hoopes, D. Strong, P. Yodzis and J. Paloheimo for discussions; D. Post, M. E. Conners and D. S. Goldberg for a preprint of a related manuscript; and the US National Science Foundation and the Institute of Theoretical Dynamics for their support.

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Correspondence to Kevin McCann.

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McCann, K., Hastings, A. & Huxel, G. Weak trophic interactions and the balance of nature. Nature 395, 794–798 (1998). https://doi.org/10.1038/27427

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