Sympatrie

Sympatry, from the Greek syn- meaning together and patria meaning homeland, is a term used in biogeography and evolutionary biology to describe a situation in which two or more populations, species, or taxa occupy the same or overlapping geographic area. This overlap enables potential interaction and gene flow, contrasting with allopatry, where populations are geographically separated, and parapatry, where ranges are adjacent with limited contact.

In the context of speciation, sympatry refers to the divergence of populations within a single geographic area, often through ecological niche differentiation, disruptive selection, or polyploidy, leading to reproductive isolation without physical barriers. However, ongoing gene flow in sympatry can complicate the process of speciation, and cases of sympatric speciation are frequently debated and studied.

Examples of sympatry include certain cichlid fishes in African crater lakes that have diversified within the same water body, as well as some plant groups where genome doubling or shifts to different host plants create reproductive barriers among locally coexisting populations. Sympatry also occurs in many other taxa where closely related species share forests, streams, or meadows.

Mechanisms associated with sympatric processes typically involve disruptive selection on ecological or mating traits, assortative mating where individuals preferentially mate with similar types, and chromosomal rearrangements that reduce recombination between emerging lineages. In practice, researchers distinguish between strict sympatry (complete range overlap) and partial or facultative sympatry (overlap only in part of the range) when describing patterns of coexistence and divergence.