American Pronghorn: Social Adaptations and the Ghosts of Predators Past

The pronghorn antelope (Antilocapra americana) evolved, it would seem, to feed a host of predators, ranging from coyotes and wolves to the long-disappeared saber-toothed tiger and American cheetah. (Cheetahs, John A. Byers writes, were probably "the principal agents of selection that prompted the evolution of astounding running speed in pronghorn"--a speed that has been clocked at 100 kilometers an hour.) Lacking many of those predators, today the pronghorn population has grown throughout the American West, making the animals a common sight for ecotourists and residents alike. Among other things considered in this thorough survey of pronghorn biology, Byers looks at "ghost behavior"--patterns of action determined by ecological conditions that long ago changed. Horses, for instance, remain herd-based social animals as a protective mechanism against predators, although, as he writes, "predator-driven selection has been relaxed."