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Competition and the Structure of Ecological Communities

Charles Elton
Journal of Animal Ecology
Vol. 15, No. 1 (May, 1946), pp. 54-68
DOI: 10.2307/1625
Stable URL: http://www.jstor.org/stable/1625
Page Count: 15
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Competition and the Structure of Ecological Communities
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Abstract

1. Analysis was made of the published ecological surveys of fifty-five animal (including some parasite) communities and twenty-seven plant communities from a wide range of habitats, and the frequencies of genera with different numbers of species tabulated. A rather constant and high percentage of genera with only one species present was found, the average being 86% for animal and 84% for plant communities. The corresponding average numbers of species per genus were 1.38 and 1.22. 2. These figures differ considerably from those of a faunal list for any large region, e.g. the percentage of genera with only one species present for eleven large British insect groups is 50, and the average number of species per genus for all British insects is 4.23. 3. The difference in species/genus frequencies between ecological surveys of relatively small parts of any general habitat, and those for faunal lists from larger regions, is attributed to existing or historical effects of competition between species of the same genus, resulting in a strong tendency for the species of any genus to be distributed as ecotypes in different habitats, or if not, to be unable to coexist permanently on the same area of the same habitat. 4. These conclusions apply at present only to the list of communities hitherto surveyed with any completeness, which does not include a sufficient sample of terrestrial habitats like heath, meadow, scrub and woodland containing many plant species. The animal communities analysed are mostly ones in which the primary consumer species depend on only a few natural resources. 5. The ability of certain groups of species, mostly separated by generic characters, to exist together on the same area while drawing upon a common pool of resources, is one of the central unsolved problems in animal community structure and population dynamics.

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