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After a geographic barrier arises, two species evolve reproductive isolation. Here, the geographic barrier is removed before complete isolation, whereby the two populations exchange genes. Low fitness hybrids may form, but reinforcement (effectively a process of mate choice discrimination) causes the completion of the speciation process.
Allopatric speciation (from Ancient Greek ἄλλος (állos) 'other' and πατρίς (patrís) 'fatherland') – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model [1]: 86 – is a mode of speciation that occurs when biological populations become geographically isolated from each other to an extent that prevents or interferes with gene flow.
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Ernst Walter Mayr (/ ˈ m aɪər / MYRE, German: [ɛʁnst ˈmaɪɐ]; 5 July 1904 – 3 February 2005) [1] [2] was a German-American evolutionary biologist. He was also a renowned taxonomist , tropical explorer, ornithologist , philosopher of biology , and historian of science . [ 3 ]
Other geneticists such as J. B. S. Haldane did not even recognize that species were real, while Sewall Wright ignored the topic, despite accepting allopatric speciation. [4]: 3 The primary contributors to the incorporation of speciation into modern evolutionary synthesis were Ernst Mayr and Theodosius Dobzhansky. [29]
Mayr emphasized the importance of allopatric speciation, where geographically isolated sub-populations diverge so far that reproductive isolation occurs. He was skeptical of the reality of sympatric speciation believing that geographical isolation was a prerequisite for building up intrinsic (reproductive) isolating mechanisms.
Geographic illustration of SPATIAL ASPECTS OF SPECIATION: allopatric speciation - physical barrier divides population; peripatric speciation - small founding population enters isolated niche; parapatric speciation - new niche found adjacent to original one; sympatric speciation - speciation occurs without physical separation; Drawn in Inkscape ...
The mechanisms of reproductive isolation have been classified in a number of ways. Zoologist Ernst Mayr classified the mechanisms of reproductive isolation in two broad categories: pre-zygotic for those that act before fertilization (or before mating in the case of animals) and post-zygotic for those that act after it. [5]