Peripatric speciation

Peripatric speciation is a mode of speciation in which a new species is formed from an isolated peripheral population. Since peripatry resembles allopatric speciation, in that populations are isolated and prevented from exchanging genes, it can often be difficult to distinguish between them. Nevertheless, the primary characteristic of peripatric speciation proposes that one of the populations is much smaller than the other. One possible consequence of peripatric speciation is that a geographically widespread ancestral species becomes paraphyletic, thereby becoming a paraspecies. The concept of a paraspecies is therefore a logical consequence of the evolutionary species concept, by which one species give rise to a daughter species. An alternative model of peripatric speciation, centrifugal speciation, posits that a species' population experiences periods of geographic range expansion followed by shrinking periods, leaving behind small isolated refugial populations; on the periphery of the main population.

The terms peripatric and peripatry are often used in biogeography, referring to organisms whose ranges are closely adjacent but do not overlap, being separated where these organisms do not occur—for example on an oceanic island compared to the mainland. Such organisms are usually closely related (e.g. sister species); their distribution being the result of peripatric speciation.

Peripatric speciation was proposed by Ernst Mayr, and is related to the founder effect, because small living populations may undergo selection bottlenecks. The founder effect is based on models that suggest peripatric speciation can occur by the interaction of selection and genetic drift, which may play a significant role in peripatric speciation.

Peripatric speciation models are identical to models of vicariance (allopatric speciation). Requiring both geographic separation and time, speciation can result as a predictable byproduct. Peripatry can be distinguished from allopatric speciation by three features: 1) the size of the isolated population, 2) strong selection caused by the dispersal and colonization of novel environments, and 3) the effects of genetic drift on small populations.

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