Allopatric speciation occurs when populations become geographically separated, whereas sympatric speciation occurs while populations remain in the same geographical area. Both require reproductive isolation and divergence until the populations form separate species.
The Mechanism
Speciation is the splitting of one species into two or more species. Under the biological species concept, separate species cannot interbreed to produce fertile offspring.
The two processes differ mainly in how reproductive isolation begins:
Feature | Allopatric speciation | Sympatric speciation |
|---|---|---|
Location | Populations occupy geographically separate areas | Populations occupy the same geographical area |
Initial barrier | A physical barrier, such as a river, mountain or ocean | A non-geographical barrier, such as different breeding behaviour, ecological niches or chromosome numbers |
Gene flow | Reduced or stopped by geographical separation | Reduced despite the populations living together |
Selection | Different environments create different selection pressures | Different niches or mating patterns create differential selection within the same area |
Example | Populations separated by the Congo River can undergo divergence |
