A MODEL TO EXPLAIN ECOLOGICAL PARAPATRY

Ecological parapatry, in which pairs of largely allopatric taxa abut a long common boundaries without hybridization, is often reported but se ldom explained. A computer simulation model is developed that shows th at parapatry between two species can be maintained by interspecific in teraction on a dine of reducing ecological suitability for the competi tively stronger species. In the model, a homogeneous environment requi res much greater interaction strength to sustain parapatry than does a heterogeneous environment with alternate regions of favorable and poo r habitat. The heterogeneous environment of the model is intended to m imic the environment near a well-studied parapatric boundary between t wo reptile tick species.