In the Southwest, chipmunks are limited to mountains high enough to support woodland or forest. Thus they extend southward along the montane fingers thrusting into the arid lands: the Sandia/Manzano/Guadalupe highlands in the east, the San Andres and Organs in central New Mexico, and the Mogollon complex in the western part of the state.
Southern populations, currently isolated by warm, arid lowlands,
seemingly form three different species. Going from west to east, we have the
Gray-necked Chipmunk; the Colorado Chipmunk; and the Gray-footed Chipmunk. Although the
differences between the populations clearly indicate that there has been a considerable
degree of differential evolution during isolation, it's not clear whether different
species, different subspecies of the same species, or some mixture of these choices is
the case. With isolated populations, we cannot apply the classic test to determine the
status. That is, if two populations freely interbreed, they are considered to be the
same species; if not, while having the opportunity, then they are considered separate
species. By them being geographically isolated, with no opportunity to breed, we're
stymied.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.