Home Range, Growth, and Population Density of Uta stansburiana in Arizona

Abstract

A population of Uta stansburiana was studied for two years in the Sonoran Desert. Mean growth rates were highest in juvenile males (5.19 mm/month) and lowest in adult females (0.31 mm/month). Average home range for 15 males was 446 m2 (convex polygon), for 15 females, 121 m2, and for 15 juveniles, 61 m2. On one study area, population density of adults decreased from 50/ha in February to 7/ha in May. Most females did not survive to lay second or third clutches. Numbers of emerging hatchlings paralleled the reduction in number of surviving females. Among 5 sub-areas, utas were most abundant in a disturbed wash and flatland site, becoming less abundant in a low-altitude mountain valley and adjacent slopes. The ecology of Uta stansburiana is well known through the studies of Tinkle and his students in Texas and Colorado (Tinkle, 1967). Other studies in Nevada and Utah have increased the knowledge of geographic variation in this species' life history (Tanner, 1965, 1972; Tanner and Jorgensen, 1963; Turner et al., 1970). There have, however, been no ecological studies of U. stansburiana in the south-central portion of its range (Arizona and New Mexico). Here I report information on U. stansburiana ecology in the Sonoran Desert of Arizona. A population of U. stansburiana was studied at Phoenix South Mountain, Maricopa County, Arizona, from October 1964 through August 1966, in the Larrea-Franseria (Lower Colorado Valley) region of the Sonoran Desert (Shreve, 1951). Research was oriented primarily toward obtaining data on home range, population density, and growth for comparison with Tinkle's work. Other data concerning this population are presented comparatively elsewhere (Parker and Pianka, unpubl). MATERIALS AND METHODS Seven areas were studied at the east end of South Mountain, west and south of the town of Guadalupe. Climatic characteristics of the location and detailed descriptions of study areas are given elsewhere (Parker, 1972). Study areas were as follows: (1) flatland shrub-1.0 km W Guadalupe, creosote bush (Larrea tridentata) and bur sage (Franseria deltoidea); (2) disturbed flatland wash-0.5 km N area 1, creosote bush, burro bush (Hymenoclea sp.), cocklebur (Xanthium saccharatum), and wolf berry (Lycium sp.); (3) north-facing slope-2.5 km W Guadalupe, bur sage, brittle bush (Encelia farinosa), paloverde (Cercidium microphyllum), and staghorn cholla (Opuntia versicolor); (4) valley -2.5 km W Guadalupe, variety of shrubs and cacti found in other areas; (5) south-facing slope-2.5 km W Guadalupe, teddybear cholla (Opuntia bigelovii); (6) flatland desert shrub grid area-1.6 km S Guadalupe, creosote bush and white bur sage (Franseria dumosa); (7) flatland desert shrub removal area-adjacent to area 6. Areas 1-5 each had 20 1-gal. can traps operated during the entire study. Traps were arranged in a zig-zag or oval course depending on terrain. Area 6 had 195 traps in a 1.1 ha grid, and area 7 had 118 traps arranged in two U-shaped lines. Areas 6 and 7 were operated from February through August 1966. Lizards were permanently marked by toe-clipping, measured for snout-vent (SVL) and tail lengths to the nearest millimeter with a clear plastic ruler, and released at the capture point. The