Name three ways isolation, or separation can occurs
groups members may be separated by a

If you're talking about Biology and the separation that occurs within a species, members of that species can be separated/isolated by geographical/environmental factors, adaptations that allow members to separate into two groups for survival/needs (food, shelter, etc.), time plays a part, but I can't remember specifically how that causes separation/isolation with a species. 

South central region

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.