Slide 45 of 47
Another example of how density dependence can operate in small populations is provided by the Allee effect (Allee 1931), i.e., the per capita birth rate declines at low densities (Fig. 8) because, for example, of the increased difficulty of finding a mate (Yodzis 1989:12-13). This is known as Allee-type behavior (of the per capita birth rate), and its effect on the per capita population growth rate, R(t), is called an Allee effect. In theory, a low density equilibrium would be sustained in a deterministic equilibrium, where the birth rate equals the death rate. However, given stochasticity, the population could be driven below the low density equilibrium, and thus slide into extinction.