Interrelationships of Feeding Habits in a Population of Lizards in Southwestern Texas

Abstract

Six species of lizards have been recorded from two study areas, one near Kermit, Winkler County, and one near Monahans, Ward County, Texas. Two of the species, Uta stansburiana and Cnemidophorus tigris, which are numerous and easily encountered, provided a number of fine samples for stomach analyses. Two others, Phrynosoma cornutum and Crotaphytus wislizeni, which are only occasionally encountered, pro- vided few specimens for stomach analyses. Two species, Holbrookia maculata and Eumeces obsoletus, are so rarely encountered as to have provided only a single specimen each. Analyses indicate that both Uta stansburiana and Cnemidophorus tigris are opportunistic feeders on arthropods. In many samples and in the summation of the foods, pre- dominant food items found in the stomachs of Uta were coleopterans and hymenopterans, and predominant items in Cnemidophorus were coleopterans and orthopterans. Competition between these two numeri- cally dominant species is avoided by utilization of different sizes of food items; small insects for Uta and larger insects for Cnemidophorus. How- ever, interspecific competition for food between the two numerically dominant species and the other species is one possible explanation for the relatively low numbers of the other species.