Coexistence under positive frequency dependence

Negative Frequency dependence resulting from interspecific interactions is considered a driving force in allowing the coexistence of competitors. Whil e interactions between species and genotypes can also result in positive fr equency dependence, positive frequency dependence has usually been credited with hastening the extinction of rare types and is not thought to contribu te to coexistence. In the present paper, we develop a stochastic cellular a utomata model that allows us to vary the scale of frequency dependence and the scale of dispersal. The results of this model indicate that positive fr equency dependence will allow the coexistence of two species at a greater r ate than would be expected from chance. This coexistence arises from the ge neration of banding patterns that will be stable over long time-periods. As a result, we found that positive frequency-dependent interactions over loc al spatial scales promote coexistence over neutral interactions. This resul t was robust to variation in boundary conditions within the simulation and to variation in levels of disturbance. Under all conditions, coexistence is enhanced as the strength of positive frequency-dependent interactions is i ncreased.