JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. INTRODUCTION In this paper we present an analysis of the demography of the lizard Uta stansburiana in southern Nevada, based primarily on observations between 1966 and 1968. The work is part of a larger long-range study of the effects of low but continuous levels of gamma radiation on natural populations of plants and animals (e.g. see French 1964; French, Maza & Aschwanden 1966, 1967; Turner, Hoddenbach & Lannom 1965; Turner et al. 1967; Turner & Lannom 1968; Turner et al. 1969a, b). Our paper is a descriptive review of time changes in the abundance of Uta over a 21-year period, with suggestions as to the immediate causes of these changes. We also review five previous studies of lizard populations and discuss specific problems associated with such research. METHODS The field work was carried out between 15 February 1966 and 15 July 1968-in Rock Valley, Nye County, Nevada, in the south-western portion of the U.S. Atomic Energy Commission's Nevada Test Site. In Rock Valley there are four 20-ac (8.1 ha) areas, one of which is exposed to gamma radiations from a centrally located '37Cs source for about 300 days a year. The irradiated area and two of the three control areas are fenced. A more detailed description is given by French (1964). Most of the work was done in plots 1-4, one within each of the 20-ac areas. In an earlier paper we compared the age distribution and sex ratio of the irradiated population with corresponding attributes of the three control populations (Turner et al. 1969b). We also reported on density changes in these populations between 1966 and 1968. Although the densities of these populations differed, their composition and patterns of annual change were essentially identical. Hence, data from all four areas have been combined in the present study. In 1966 our sampling extended over four 2i0 ha quadrants. In 1967 and 1968 sampling was restricted to four 1*44 ha areas. Other observations were made in plot 5 (1.13 ha), about 1 mile (1 6 km) north-east of the experimental area. Female lizards were collected from various places with Rock Valley during the spring of 1966, 1967 and 1968, and seasonal changes in clutch size were inferred from counts of follicles, eggs and corpora lutea (see Hoddenbach & Turner 1968). Density of Uta Absolute densities of Uta in plots 1-4 were determined each spring by attempting to count completely all resident individuals. Each plot was worked by two or three people * Present address: P.O. Box 236, Zion National Park, Springdale, Utah 84767, U.S.A. 506 Demography of the lizard Uta stansburiana during 1 week of eac...

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Desert lizards occupying a 20—acre experimental facility continuously exposed to gamma radiation sustain tissue doses which are less than the cumulative free—air dose. Vegetation and terrain afford some shielding, but time spent below ground is the major source of protection. We estimate that, in the course of a year, tissue doses sustained by Uta stansburiana are from 0.3 to 0.6 of the cumulative free—air dose, and that about 1/3 of the total dose is experienced between June and August. Cnemidophorus tigris spends less time above ground, and sustains annual doses representing only about 0.1 to 0.2 of total incident gamma radiation. The dose experience of Crotaphytus wislizeni is intermediate to the other two species. Dose regimes experienced by Uta stansburiana in the experimental area are not acutely lethal.