Each animal has its own set of conditions under which it can thrive. This shows up dramatically where the ranges of two competitive species come together without being able to overlap. In sync with climatic and vegetational changes, the species advance and retreat, reversing the direction of their dance with each swing of the climate.
Pocket gophers are notoriously antisocial rodents. So antisocial, in
fact, that different species seldom overlap in their geographic ranges. One study in
the Chihuahuan Desert region followed the movements of two kinds distributed along an
arroyo. Botta's Pocket Gopher held the moister higher parts, while the Yellow-faced
Pocket Gopher inhabited the drier, down-arroyo area. Year to year climatic changes
correlated closely with fluctuations in the frontier between the two species. In dry
years, the line of demarcation retreated up-slope, only to retreat again downwards
during years of greater moisture. A bit farther north, near Santa Fe, New Mexico, the
ratio of skeletal remains of the two species from an archaeological site varied through
time—mute reminders of past cycles of drought and rain.
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.