The grand canyon was carved out by the colorado river. this caused the separation of members of a squirrel species. abert’s squirrel lives on the southern side of the canyon and in other parts of the united states. a subspecies, the kaibab squirrel, is found around the northern rim of the canyon and nowhere else in the country. as shown here, the two squirrels differ in body and tail coloration. their ears are also different. these variations are the result of what?

The correct answer would be geographic isolation.

Geographic isolation is a type of isolation in which organisms of the same species are prevented from exchanging genetic due to the separation of the organisms through physical structures such as a river, mountain et cetera.

For example, the squirrels were separated through the Colorado River.

Over generations, organisms evolve new traits as an adaptation towards different habitats.  

For example, the squirrels evolved different ears, tails, and body type.

Over several generations, accumulation of genetic variations makes the two populations so different that they can not interbreed with each other.

Thus, the populations evolved into different species.