Allee effect

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

Description

The Allee effect was described by its namesake Warder Clyde Allee. The theory states that, for very small populations, the reproduction and survival rates of individuals increases with population density. This contrasts with small populations in which increasing population density reduces the growth rate of the population.

This is a departure from the logistic growth equation

<math>fracfrac = r - frac,N</math>

where

N = population size;

r = intrinsic rate of increase;

K = carrying capacity; and

dN/dt = rate of increase of the population

In the logistic growth equation the left hand side of the equation represents the per capita population growth rate, which is dependent on the population size N, and decreases with increasing N throughout the entire range of population sizes. In contrast, when there is an Allee effect the per-capita growth rate increases with increasing N over some range of population sizes .

When a population is made up of small sub-populations additional factors to the Allee effect arise.

If...
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