Parapatric speciation is a form of speciation that occurs when populations of a species are geographically separated but still share a common border. In this scenario, individuals from different populations can interbreed in the overlapping area, but environmental differences lead to variations in traits. Over time, these differences can result in the emergence of new species. This process often happens in habitats that change gradually, such as along a mountain range or river. As populations adapt to their specific environments, reproductive barriers may develop, preventing them from mating successfully with individuals from the other population. This gradual divergence can ultimately lead to the formation of distinct species.