Originally only one squirrel species inhabited the Ponderosa pine forest around the rim of the Grand Canyon, the Abert squirrels. About 10,000 years ago when Arizona's Grand Canyonwas formed, the squirrels were separated into two species - the Abert squirrels, who inhabit the south rim; and the Kaibab squirrels, who inhabit the north rim. One population of squirrels had become two separate populations that could no longer reproduce. These squirrels are an excellent example of
genetic equilibrium.
stabilizing selection.
selection on single-gene traits.
speciation.