A Model to Explain Ecological Parapatry

Ecological parapatry, in which pairs of largely allopatric taxa abut along common boundaries without hybridization, is often reported but seldom explained. A computer simulation model is developed that shows that parapatry between two species can be maintained by interspecific interaction on a cline of reducing ecological suitability for the competitively stronger species. In the model, a homogeneous environment requires much greater interaction strength to sustain parapatry than does a heterogeneous environment with alternate regions of favorable and poor habitat. The heterogeneous environment of the model is intended to mimic the environment near a well-studied parapatric boundary between two reptile tick species.