Explaining the excess of rare species in natural species abundance distributions


The observation that a few species in ecological communities are exceptionally abundant, whereas most are rare, prompted the development of species abundance models1,2,3. Nevertheless, despite the large literature on the commonness and rarity of species inspired by these pioneering studies, some widespread empirical patterns of species abundance resist easy explanation4. Notable among these is the observation5 that in large assemblages there are more rare species than the log normal model predicts6,7. Here we use a long-term (21-year) data set, from an estuarine fish community, to show how an ecological community can be separated into two components. Core species, which are persistent, abundant and biologically associated with estuarine habitats, are log normally distributed. Occasional species occur infrequently in the record, are typically low in abundance and have different habitat requirements; they follow a log series distribution. These distributions are overlaid, producing the negative skew that characterizes real data sets.

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Figure 1: The pattern of abundance and persistence in the fish community of Hinkley Point, Bristol Channel.
Figure 2: Switch from log series to log normal model revealed by Simpson's index.
Figure 3: Using the variance/mean ratio to decompose the distribution.


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We thank R. Seaby and R. Somes for assistance with fieldwork.

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Correspondence to Anne E. Magurran.

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Magurran, A., Henderson, P. Explaining the excess of rare species in natural species abundance distributions. Nature 422, 714–716 (2003). https://doi.org/10.1038/nature01547

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