Allee effect, sexual selection and demographic stochasticity

The negative frequency-dependent effect of reproductive success in animals on population growth refers to a category of phenomena termed the Allee eff ect. The mechanistic basis for this effect and hence an understanding of it s consequences has been obscure. We suggest that sexual selection, in parti cular female mate preferences, is a previously neglected component giving r ise to the Allee effect. Lack of breeding and reduced reproductive success of females at low population densities are commonly described in situations where females have little or no opportunity to choose a mate, consistent w ith this suggestion. We developed a demographic model that incorporated the effects of lack of female choice on rates of reproduction. Using either a mating system with incompatibility or a system with a directional mate pref erence, we show that commonly encountered levels of reproductive suppressio n in the absence of suitable mates in a population, where sexual selection still operates, may increase the effects of demographic stochasticity consi derably.