Final answer:
Allopatric speciation is when geographical segregation leads to the interruption of gene flow, facilitating the divergence of species. Through processes of dispersal or vicariance, populations evolve independently due to different selection pressures, leading to the formation of new species.
Step-by-step explanation:
The type of speciation where biological processes interrupt gene flow is known as allopatric speciation.
Allopatric speciation occurs when a population is geographically divided into separate groups, which disrupts the gene flow between them. These groups may be separated by physical barriers such as mountains, rivers, or vast distances. The two key processes involved are dispersal, where members of a species move to a new geographical area, and vicariance, where a natural barrier arises to physically divide organisms. As a result, the isolated populations may undergo different evolutionary trajectories due to various selection pressures and mutation events, leading to divergent adaptations and the formation of new species. Instances such as the northern and Mexican spotted owls illustrate this phenomenon, where geologic events like ice ages likely caused the initial separation and subsequent speciation.
Moreover, the environment plays a significant role in allopatric speciation. For instance, if two rodent populations become divided by a new lake, gene flow would be obstructed, making speciation more likely. However, two flying insect populations in separate valleys might still interbreed, allowing gene flow to continue. The unique biology of an organism and its dispersal capabilities thus greatly determine the possibility of allopatric speciation.