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Species Concepts and Reproductive Isolating Barriers

Author(s): Tadzia GrandPré, PhD, Nancy Moreno, PhD, and Lisa Marie Meffert, PhD
Showing Results for: biological evolution Return to Presentation

Modes of Speciation

Many biologists interpret "species" as the fundamental unit into which populations of organisms can be classified. However, what is considered to constitute a species varies by taxonomic group as well as the purpose for which this classification is being used. The biological species concept, which defines species as interbreeding populations that are reproductively isolated from other populations, is a useful definition, particularly for thinking about how many species of sexually reproducing animals and plants arise.

There are four geographic modes of speciation that are based on the extent to which the incipient species (populations that are in the process of forming distinct species) are geographically isolated from one another. Allopatric speciation occurs in populations that became separated by a geographic barrier. Peripatric speciation, also known as founder effect speciation, is a special type of allopatric speciation. It occurs when a small population becomes isolated from its parent species. Parapatric speciation arises between neighboring populations that share small zones of contact and exhibit modest gene exchange. Sympatric speciation occurs within a single, freely interbreeding population, and is believed to occur only rarely. These modes were first described for animals and also are useful for distinguishing patterns of speciation in plants.