Foraging Ecology of the Fringe-Toed Lizard, Uma inornata, during Periods of High and Low Food Abundance

Omnivorous foraging was recorded in the fringe-toed lizard Uma inornata (Phrynosomatidae) during both high and low food resource periods, May and July 1986. Diet changed as a function of food abundance and distribution. Numbers of food items in the environment and the diet decreased by one-half from spring (May) to summer (July). Lizards ate flowers and plant-dwelling arthropods during spring, but as these foods declined, lizards shifted to leaves, ants, and ground arthropods. Ants were abundant in environmental and stomach samples, and large arthropods and lizard hatchlings were eaten when available. The diet also varied in response to changes in food abundances within microhabitats. Croton (Croton californicus), for example, showed little to no arthropod activity (determined by arthropod sampling) in July, and in response, no female and few male lizards were observed using that microhabitat in the summer. The food and resource use of male lizards differed from females but only in May. Male dietary niche breadths were narrow in the spring and expanded to include other foods in the summer; female dietary niche breadths were opposite to those of male lizards. These differences may be due to reproductive activities in the spring and a decreased abundance of food in the summer.