If allopatric speciation is the most prevalent mode of speciation, what do you predict about the geographic distributions of many closely related species? Does your answer differ for species that are sedentary versus species that are highly mobile?

It is likely that the emergence of geographical barriers among populations (such as for example, rivers, mountains, etc.) were responsible for the isolation of these species.  

Explanation:

The presence of geographical barriers among populations ensure that they begin to evolve independently and mechanisms of reproductive isolation will appear among them

most community's take hundreds of years to become stable