The Allee effect is a phenomenon in biology characterized by a positive correlation between population density and the per capita growth rate.

Contents 1 Description 2 Causes 3 Strong vs weak Allee effect 4 References 5 External links

[edit] Description

The Allee effect was first written on extensively by its namesake Warder Clyde Allee. The general idea is that for smaller populations, the reproduction and survival rates of individuals increase with population density, although this effect usually disappears as increased intraspecific competition occurs.

[edit] Causes

The effect may be due to any number of causes. In some species, reproduction—finding a mate in particular—may be increasingly difficult as the population density decreases in large areas. The Allee effect either limits that small population to a small area where they grow, or the population dies off. Other species may use strategies (such as schooling in fish) that are more effective for larger populations.

[edit] Strong vs weak Allee effect

A distinction is made between a "strong Allee effect", where a population exhibits a "critical size or density", below which the population declines on average, and above which it increases on average, and a "weak Allee effect", where a population lacks a "critical density", but where, at lower densities, the population growth rate rises with increasing density.

[edit] References

• Allee, WC, Emerson, AE, Park, O, Park, T and Schmidt, KP (1949). Principles of animal ecology.
• Leviton DA and McGovern TM (2005) "The Allee Effect in the Sea" in Marine conservation biology: the science of maintaining the sea's biodiversity, Eds: Norse EA and Crowder LB. ISBN 9781559636629
• Stephens, PA, Sutherland, WJ and Freckleton, RP (1999). "What is the Allee effect?", Oikos, 87, 185-90.

[edit] External links

• Berryman, AA (1997). Underpopulation (Allee) effects, Entomology Department, Washington State University. Retrieved 19 May 2008.
• Allee effect, Warner College of Natural Resources, Colorado State University. Retrieved 19 May 2008.
• Stephens, PA, Sutherland, WJ and Freckleton, RP (1999). "What is the Allee effect?" (summary), Oikos, 87, 185-90, at Evolutionary Biology Group, Department of Zoology, University of Oxford. Updated 22 November 2005. Retrieved 19 May 2008
• Classics: the Allee effect

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