Question

Biogeographic isolation separates of a species through geographical and biological forces.

Answer 1

populations is the answer

Answer 2

Biogeographic isolation refers to the separation of the members of the similar species, or a group of organisms, which breed and generate offspring that can further give rise to young ones.  

The separation can be achieved by the geographical forces like oceans, rivers, and mountains, and by the biological forces, like hunting times, and spring or fall mating.