This is my storyboard for the Speciation process of Abert's and Kaibab squirrels, who reside on separate rims of the Grand Canyon, AZ
These squirrels all live together in a nice green grassy area. They can all breed and reproduce with no problems. Most of the squirrels are similar in color and they mostly live up in trees and feed on Ponderosa pines. They are able to reproduce with no problems and live a healthy life. This was before the event that caused the squirrel population to be split into two different areas.
The land separated due to erosion and allowed a river to pass through, which separated the population of the squirrels. They now lived on two different sides and this is where the start of the new type of squirrel began. The two sides that each species would live on would be the North and South side of the Grand Canyon, AZ. The North Rim has a higher elevation whereas the South Rim has a lower elevation.
The Kaibab squirrels live on the North Rim so they are at a higher elevation. They travel on the ground since there aren't many trees to leap onto. The Abert Squirrels live at the South Rim which is way lower than the north rim. These completely different environments will change the characteristics and behavior of the squirrels.
The squirrels eventually meet but they can't interbreed due to reproductive mechanism barriers that cause that. There are now different colors of these squirrels and different characteristics The Kaibab squirrel moves on foot on the ground and is usually seen on dry areas. The Abert squirrel is usually found traveling through trees and being in pine trees. There is a possibility of being able to breed but it would have to be the right squirrels.
The links are cited from where I got my answers and ideas from.