Ecological Relationships Among Arboreal Desert Lizards

Three arboreal desert lizards (Urosaurus graciosus, U. ornatus, and Sceloporus magister:Iguanidae) occur in close association in riparian habitats of central Arizona. The lizards were studied over 2 yr, to determine patterns of resource utilization. Urosaurus graciosus and U. ornatus are similar in body size, but Sceloporus magister is much larger. Juvenile S. magister are, however, similar in body size to adults of both Urosaurus. Ratios of head and body size (larger species:Smaller species) reveal similarities between the Urosaurus species and between both species of Urosaurus and juvenile S. magister, but large differences between Urosaurus species and adult S. magister. Active body temperatures of all three species were similar, and the only significant difference in time of activity was between S. magister and U. ornatus. The habitat of U. graciosus reached higher air and substrate temperatures than that of U. ornatus and received greater incident radiation (S. magister occurred in both habitats). Urosaurus ornatus and S. magister avoid extremes of temperatures by entering crevices in trees, retreating under loose bark, or entering mammal burrows or nests, whereas U. graciosus retreat to shaded portions of tree trunks and are thus less able to avoid extremes. Urosaurus graciosus occur in relatively small trees and forage in the canopy; U. ornatus inhabit large trees and forage on trunks and large limbs; S. magister occupy trees of all sizes but forage primarily on trunks and large limbs, and on the ground. Prey sizes were significantly different among species and with one exception (S. magister), significantly different within species among years. Diets of all three change seasonally and yearly, presumably in association with resource availability. Diet overlaps are often high but fluctuate seasonally and yearly. Data on resource availability suggest that all species exploit the temporally abundant insects. Data presented on habitat utilization, activity times, body temperatures, and food eaten reveal partitioning of the arboreal habitat in three dimensions between U. graciosus and U. ornatus and partitioning of prey size between the two Urosaurus as a group, and S. magister.