The Chihuahuan Desert lizards Uma e. exsul and U. e. paraphygas are morphologically and ecologically less specialized for life on loose aeolian sand than are the other species of the genus. They do not occur in large areas of vegetationless sand, and are probably limited to areas in which rodents can maintain open burrows year-round. Uma exsul use these burrows to escape from predators and for nocturnal retreat. Only in an area with very dense, low-growing vegetation did we see them bury in loose sand at night. Unlike other species in the genus, U. exsul occurs on dunes in which a large amount of silt is mixed with the sand, and it also lives on hardened silt substrates side by side with Holbrookia maculata. Body temperatures of active U. exsul averaged 38.7 C (S.E. = 0.4, n = 45), the same as other species in the genus, but U. exsul begin activity later in the morning than do the specialized forms. In this respect the behavior of U. exsul is like Callisaurus. Like the other species in the genus, U. exsul shows no physiological adaptations for sand-swimming; heart rates of buried lizards are lower than those of lizards on the surface, but the difference reflects inactivity, not a submergence bradycardia.
Department, Program, or Center
Thomas H. Gosnell School of Life Sciences (COS)
Copeia 1978N1 (1978) 81-86
RIT – Main Campus