Allopatric speciation occurs when a group of individuals of a species becomes isolated and differentiates into one or more new species that can no longer reproduce with members of the original group. There are several factors required for allopatric speciation to occur like isolation, time and natural selection. Earthquakes, floods and migration are ways a group of individuals of the same species can become isolated. The emergence of a new species can take just a few generations or even thousands or millions of years to occur. The process of natural selection causes the adaptive genetic changes that result in the formation of the new species.
The image above shows an allopatric speciation experiment using fruit flies and different food sources.
References
- OpenStax, Biology. OpenStax. May 20, 2013. http://cnx.org/content/col11448/latest/