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A test of the unified neutral theory of biodiversity


One of the fundamental questions of ecology is what controls biodiversity. Recent theory suggests that biodiversity is controlled predominantly by neutral drift of species abundances1,2,3,4. This theory has generated considerable controversy5,6,7,8,9,10,11,12, because it claims that many mechanisms that have long been studied by ecologists (such as niches) have little involvement in structuring communities. The theory predicts that the species abundance distribution within a community should follow a zero-sum multinomial distribution (ZSM), but this has not, so far, been rigorously tested. Specifically, it remains to be shown that the ZSM fits the data significantly better than reasonable null models. Here I test whether the ZSM fits several empirical data sets better than the lognormal distribution. It does not. Not only does the ZSM fail to fit empirical data better than the lognormal distribution 95% of the time, it also fails to fit empirical data better even a majority of the time. This means that there is no evidence that the ZSM predicts abundances better than the much more parsimonious null hypothesis.

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Figure 1: Approach to equilibrium of a local community.
Figure 2: Deviations from observed abundances depends on the stopping rule.
Figure 3: Comparing the fitted and actual BCI data.


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I thank the numerous volunteers who spent many hours collecting the BBS data, and the professionals at Patuxent Wildlife Research Center, who have put the data into an accessible, high-quality format, as well as those who collected and published the enormously valuable BCI data set. I also thank M. Rosenzweig, B. Enquist and the students in their laboratories for stimulating my thinking in this area. The National Science Foundation provided funding for this research. B. Walsh was a useful sounding board on statistics. Finally, I thank S. Marx, M. Weiser, D. Faulk and W. Turner for suggestions on an earlier draft of this paper, especially M. Weiser for his clarity on the importance of stopping rules, and S. Marx for greatly increasing the clarity of the paper.

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Correspondence to Brian J. McGill.

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McGill, B. A test of the unified neutral theory of biodiversity. Nature 422, 881–885 (2003).

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