(of biological species or speciation) Describing formation of two (or more) different species or populations that inhabit the same or overlapping geographical area so that the opportunity to interbreed is presented.
Sympatry is one of three theoretical models for the phenomenon of speciation. In complete contrast to allopatry, species undergoing sympatric speciation are not geographically isolated by a natural barrier, for example, a mountain or a river. The speciating populations share the same territory.

(compare: Allopatric, Parapatric)