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Simple rules yield complex food webs


Several of the most ambitious theories in ecology1,2,3,4,5,6,7,8,9,10,11,12,13,14 describe food webs that document the structure of strong and weak trophic links9 that is responsible for ecological dynamics among diverse assemblages of species4,11,12,13. Early mechanism-based theory asserted that food webs have little omnivory and several properties that are independent of species richness1,2,3,4,6. This theory was overturned by empirical studies that found food webs to be much more complex5,7,8,9,14,15,16,17,18, but these studies did not provide mechanistic explanations for the complexity9. Here we show that a remarkably simple model fills this scientific void by successfully predicting key structural properties of the most complex and comprehensive food webs in the primary literature. These properties include the fractions of species at top, intermediate and basal trophic levels, the means and variabilities of generality, vulnerability and food-chain length, and the degrees of cannibalism, omnivory, looping and trophic similarity. Using only two empirical parameters, species number and connectance, our ‘niche model’ extends the existing ‘cascade model’3,19 and improves its fit ten-fold by constraining species to consume a contiguous sequence of prey in a one-dimensional trophic niche20.

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Figure 1: Diagram of the niche model.
Figure 2: Distribution of normalized errors between empirical data and model means for all properties of the random, cascade and niche models.
Figure 3: The niche model's normalized errors for each property of each food web.
Figure 4: Mean normalized error of each property for each model averaged across the seven food webs (Table 1).


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We thank J. Dunne, M. Geluardi, E. Connor, L. Goldwasser, J. Harte, T. Parker, E. Berlow and I. Billick for comments and suggestions. The USA National Science Foundation provided support.

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Williams, R., Martinez, N. Simple rules yield complex food webs. Nature 404, 180–183 (2000).

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