Parapatric speciation



Parapatric speciation is a form of speciation that occurs due to variations in mating frequency of a population within a continuous geographical area. In this model, the parent species lives in a continuous habitat, in contrast with allopatric speciation where subpopulations become geographically isolated. Niches in this habitat can differ along a environmental gradient, hampering gene flow, and thus creating a cline.

An example of this is the grass Anthoxanthum, which has been known to undergo parapatric speciation in such cases as mine contamination of an area. This creates a selection pressure for tolerance to those metals. Flowering time generally changes (in an attempt at character displacement&mdash;strong selection against interbreeding&mdash;as the hybrids are generally ill-suited to the environment) and often plants will become self-pollinating.

Another example is ring species.