Allee effect

Allee effect

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


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 of individuals decrease. This effect usually saturates or disappears as populations get larger.


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. Other species may use strategies (such as schooling in fish) that are more effective for larger populations.

trong 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 at an increasing rate.


Allee, WC, Emerson, AE, Park, O, Park, T and Schmidt, KP (1949). "Principles of animal ecology".

Stephens, PA, Sutherland, WJ and Freckleton, RP (1999). "What is the Allee effect?", "Oikos", 87, 185-90.

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.

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