This is a book about change,"" say the Grahams, who work background information about adaptation and interdependence into a series of examples of how humans have changed and are changing the desert regions of the American southwest. The burro, imported from North Africa, is crowding out the native bighorn sheep, and a current dispute centers on a Bureau of Land Management-favored policy of shooting the burros. Cactus rustlers sell their loot to plant stores and have attempted murder on the Arizona lawman who tracks them down; the annual Barstow-to-Las Vegas motorcycle race has destructive effect on life along its route; overgrazing by cattle destroys vegetation; and human population in general is depleting the groundwater supply. On the plus side, the Mexican gray wolf who once roamed the southwest is being preserved at a Tucson museum, and research at the University of Arizona seeks uses for native plants that could be cultivated. The Grahams are easier on ranchers than on bikers and poachers, and they don't mention large farms and other commercial interests in connection with groundwater use. Blandly, they cite education of the public by government agencies as the area's best hope. But as far as they go, which is presenting natural history in terms of change and in a contemporary context, their lesson is enlightening and livelier than most introductions to the desert.