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 inornat a (Phrynosomatidae) during both high and low food resource periods, Ma y and July 1986. Diet changed as a function of food abundance and dist ribution. Numbers of food items in the environment and the diet decrea sed by one-half from spring (May) to summer (July). Lizards ate flower s and plant-dwelling arthropods during spring, but as these foods decl ined, lizards shifted to leaves, ants, and ground arthropods. Ants wer e 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 act ivity (determined by arthropod sampling) in July, and in response, no female and few male lizards were observed using that microhabitat in t he summer. The food and resource use of male lizards differed from fem ales but only in May. Male dietary niche breadths were narrow in the s pring and expanded to include other foods in the summer; female dietar y niche breadths were opposite to those of male lizards. These differe nces maybe due to reproductive activities in the spring and a decrease d abundance of food in the summer.