A Demographic Analysis of Fenced Populations of the Whiptail Lizard, Cnemidophorus tigris, in Southern Nevada

Abstract

Between 1964 and 1967, spring densities of Cnemidophorus tigris in four study areas in southern Nevada ranged from 3-8 per acre. Estimated biomass ranged from around 43 to 114 g/acre. The sex ratio was 1:1. Minimal annual survival of adults was 54-60%, and life-spans of at least 7 years are postulated. An undetermined proportion of mature females laid two clutches of eggs in 1965, but the general pattern was one clutch of 2-4 eggs per year. Large females produced more eggs than small ones. Occasionally females 9-10 months of age laid eggs, but sexual maturity normally was attained at about 21 months. By assuming that all mature females laid two egg clutches in 1965 our fecundity estimates could be approximately reconciled with the observed size and age composition of populations in the spring of 1966. Possible compensatory errors in this analysis are discussed. One of the challenging problems of contemporary ecology is the analysis of ecosystems and the development of mathematical models capable of simulating the trophic transfers of energy and materials and the interactions between species which collectively constitute ecosystem function. This endeavor requires not only an understanding of the processes of primary production, but also the roles of primary and secondary consumers. The net production and material transfers of a consumer population can be estimated only if one understands the time changes in the structure and size of such populations, i.e., the rates of age-specific mortality and the schedule of recruitment by which the population is sustained. In another paper we have discussed the demography of Uta stansburiana and related annual changes in densities of this species to changes in schedules of female survival and fecundity (Turner et al., 1 Present address: PO Box 236, Zion National Park, Springdale, Utah 84767