Final answer:
Sympatric speciation occurs when two populations of the same species become two different species within the same geographical region, as opposed to allopatric speciation which involves geographic separation.
Step-by-step explanation:
When two populations of the same species genetically diverge to become two species despite being located in the same geographical region, sympatric speciation has occurred. This contrast with allopatric speciation, where populations become geographically separated and diverge into new species due to the lack of gene flow and different environmental pressures.
In sympatric speciation, a new species evolves from a single ancestral species without geographic isolation. The mechanisms that lead to sympatric speciation can include genetic mutations, changes in habitat preferences, or differences in mating behavior that reduce gene flow within the same area, eventually leading to reproductive isolation and therefore speciation.