Parapatry

Parapatry is a type of speciation in the theory of natural selection . It occurs when the zones of two species with a similar ecologicalniche but do not overlap. The concept of parapatry is necessary to satify the postulate of natural selection that two speciescannot co-exist in the same location over the longer term with the same ecological niche. It suggests that there may be somefactor apart from distance or ecological role which keeps the two species apart.

It contrasts with allopatry where different species are geographicallyisolated from each other, and sympatry where different species evolve in the samearea by finding different ecological roles. If there is a zone where hybridisation occurs providing gene flow between the two base populations, then it is questionable whetherthey are indeed distinct species. Parapatry is relatively uncommon in temperate areas, but can be seen more often in tropical areas. Examples of the boundariesbetween two species include a change in elevation or a crossable river.