Answer:
The answer to the proposed situation, the differences between two species of squirrels from the area of the Gran Canyon, who probably had a common ancestor before the change in landscape forced them to naturally adapt, and change, would be: biological adaptation.
Step-by-step explanation:
Biological adaptation is known as the expression of certain traits in response to the stimulation brought by an environment. In this case, the squirrels, even though they have a common ancestor, were brought apart by landscape differences. Thus, each one had to face different environmental situations that forced them to adapt. Because each environment: one living on the southern side of the canyon, and the other only on the northern side, is different, and demands differently from the species, they had to biologically adapt to it, and thus, their genetics phenotypically expressed the necessary traits to survive in their new conditions.