ScienceDaily (May 13, 2005) — Competition is a pervasive feature of life. Yet, how can so many organisms coexist when some must be better competitors than others? In a study to be published in the July 2005 issue of The American Naturalist, researchers show that chance may play a role in coexistence because, although poor competitors generally lose, they may occasionally get lucky.

Using theory developed for population genetics, the study demonstrates that stochastic events may override competitive ability in determining the outcome of competition: inferior competitors are relatively more likely to emerge victorious in ecological communities where the role of chance is increased because communities are small, shrinking, or both. When communities are large or increasing in size, the opposite is true: superior competitors are more likely to win.

This work extends previous models of coexistence by suggesting that inferior competitors need not rely solely upon superior dispersal ability to persist with better competitors. Results can also help explain why biological invasions frequently occur in communities that have been degraded and fragmented by anthropogenic activities, because rapid reductions in the size of communities make it relatively more likely that inferior exotic species will usurp native species, even if natives are better competitors. Given ongoing habitat change and the incalculable costs of biological invasions, stochasticity may have consequences for competitive interactions that are anything but lucky.

Sponsored by the American Society of Naturalists, The American Naturalist is a leading journal in the fields of ecology and evolutionary biology and animal behavior. For more information, please see our website: www.journals.uchicago.edu/AN

John L. Orrock and Robert J. Fletcher, Jr., "Changes in community size affect the outcome of competition" 166:1 July 2005.

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