Animal and plant ranges are pretty much in constant flux. This is especially evident when we look at distributional changes during the last ice age and in the warming, drying time immediately after. We often use such changes in distribution to hypothesize the nature of climatic changes, for most organisms are either directly affected by climate or indirectly affected through changes in vegetation that in turn are dependent on climatic factors.
There is, though, one factor that tends to trip us up chronologically.
Namely, it takes time for plants and animals to expand their ranges, and likewise,
organisms may hang on for awhile in favored areas even after the regional climate is no
longer suitable. We now know that some climatic changes occur very rapidly and may
outpace the ability of organisms to keep up. For example, Sagebrush Voles now occur in
south to south-central Utah, but fossils are found on the Mexican Border. Even if
running full-tilt on their 3/4-inch legs, it'd take ages to traverse that distance.
And for a lazy vole? Who knows?
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.