Final answer:
Genetic divergence in parapatry is similar to sympatric speciation as both can occur without physical geographical separation, with reproductive isolation and adaptive radiation facilitating new species formation.
Step-by-step explanation:
Genetic divergence in parapatry is similar to sympatric speciation because both can occur without physical barriers separating populations within the same geographic area. In sympatric speciation, divergent evolution results from internal factors like ecological niches or behavioral isolation, rather than external physical barriers. For instance, a population might split into groups with different feeding habits within the same environment, as observed with fish living in a lake who start exploiting different food resources at varying depths. Over time, the resulting reproductive isolation can lead to speciation, with genetic differences accumulating between the groups.
An example of sympatric speciation involves the East African cichlid fish, which show a pattern of adaptation to different lighting conditions in their aquatic habitat, affecting mate selection based on coloration. This kind of speciation is also evidenced by cichlid fish in Lake Victoria, which demonstrate significant morphological and dietary distinctions that have arisen without the influence of polyploidy. In both cases, reproductive isolation and adaptive radiation have facilitated the formation of distinct species within the same geographic location.