Allopatric Speciation

Species emergence through geographic isolation

Allopatric speciation is considered one of the main reasons for the emergence of new species and requires a geographic isolation of at least two subpopulations. Reasons for this type of geographical separation can be, for example:

 Continental drift

 Orogeny

 Climate change (eg desertification or change in sea level)

 Random drifting into isolates (e.g., islands, see Darwin's finches)

Since henceforth no gene flow (no possibility to exchange alleles) exists more between the two populations, the subpopulations develop due to different selection factors, mutations and also different alleles in the gene pool apart. The selection factors work differently because the environmental conditions in both areas are not the same. Mutations occur by chance and therefore do not affect both populations equally. And finally, the bottleneck effect ensures an unequal distribution of alleles in the gene pool. It is conceivable that certain alleles are present only in one of the two subpopulations.

Schematic example of allopatric speciation

1. Source population

2. Sudden geographic barrier divides the population into two subpopulations. From now on, there is no more gene flow. Theoretically, the exchange of alleles would still be possible.

3. Random and different mutations occur in the populations

4. The mutations spread in the gene pool of the respective subpopulation. Furthermore, a different selection pressure in the respective populations additionally ensures a different development.

5. The geographical barrier has been lifted. Gene flow between the two subpopulations is no longer possible (see reproductive isolation) because the populations have evolved too much. Result: One kind became two!

Summary

Allopatric speciation describes the emergence of species due to geographical isolation.

Causes of this geographic isolation are e.g. Continental drift, orbit or climate change.

Mutations and a different selection pressure provide for a non-convergent development of the two subpopulations, so that they are at some point reproductively isolated from each other.