Some regions of the Southwest have two or even three species of chipmunks. These small, striped squirrels are isolated in highland areas, unable to pass from one mountain range to another because of surrounding arid conditions. Since the formation of new species commonly requires geographic isolation, the question arises: how do we end up with different, related species in the same mountain range?
The answer lies in climatic changes. As the ice sheets waxed and waned to the north, intervals of cooler, wetter seasons alternated with times as warm and dry as today in the Southwest. During some such cool spell, chipmunks reached our Southwestern mountains and then, isolated between major glacial periods, speciated, joined during later glaciations by the other species nurtured in former isolation. It's also possible that, instead, far-flung populations of chipmunks speciated elsewhere. Regardless, our fickle climate has allowed multiple invasions.
Other animals and plants followed much the same scenario, resulting in
our region's high level of biological diversity. Just as in personal affairs,
climatic ups and downs make for an interesting life.
Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.
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.