The Satyr Effect: A Model Predicting Parapatry and Species Extinction

Abstract

A "satyr" is any male that successfully mates and reduces the reproductive success of a female of a different species or population. We sought to model the interaction of such potentially intermating species that are initially isolated in space but come to occupy overlapping niches. This model incorporates logistical growth curves, Lotka-Volterra interspecific competition, the satyr effect, and dispersal of the populations to neighboring demes. Both parapatry and extinction can occur in the presence of asymmetrical population parameters, depending on the dispersal characteristics of the interacting species. Parapatry is predicted at small migration constants, whereas extinction will occur at large ones. Species extinction may result from reproductive competition (satyrization) alone. Parapatry will be stable in relatively sessile organisms interacting through satyrs even in the absence of competition for common resources. The outcome of interactions between two species thus results from both trophic and reproductive competition.