Two squirrel varieties (the Abert squirrel and the Kaibab
squirrel) have a common ancestor that lived in Northern
Arizona. About 10,000 years ago, the Grand Canyon was
carved out of land in Northern Arizona, leaving populations
of the ancestral squirrel species separated from one
another. Today, in the area of the Grand Canyon, the Abert
squirrel lives only on the canyon's south rim, while the
Kaibab squirrel lives on the north rim.

What type of speciation has occurred between these two varieties of squirrels?
A. Reproductive isolation
B. Disruptive selection
C. Temporal isolation
D. Behavioral isolation
Tan