Life History Phenomena in Two Populations of the Lizard Sceloporus undulatus in Southwestern New Mexico

Abstract

Fecundity, survivorship and population characteristics were determined for the lizards Sceloporus undulatus consobrinus and S. u. tristichus in southwestern New Mexico. Sceloporus u. consobrinus lays at least four clutches per year with a mean clutch size of 9.9 eggs. Sceloporus u. tristichus lays at least two clutches per year with a mean clutch size of 7.2 eggs. The deviations about the regressions of clutch size on snout-vent length were significantly different between the two subspecies. In S. u. tristichus, eggs are heavier, survivorship higher, predation (as estimated by tail loss frequency) lower, mean adult size smaller, and the population is more dense than in S. u. consobrinus. The S. u. tristichus population is probably closer to K (environmental carrying capacity) than that of S. u. consobrinus. The life history and population characteristics of other populations of the S. undulatus group were compared in light of current concepts of rand K-selection, and these concepts were evaluated. INTRODUCTION Intraspecific variability in the life history characteristics of age at maturity, juvenile survivorship, adult life expectancy, clutch size and age-specific fecundity was described for the lizard Sceloporus undulatus by Tinkle and Ballinger (1972) and Tinkle (1972). Tinkle compared population and life history phenomena in seven populations of S. undulatus to gain insight into the evolution of life history differences among lizards. The purposes of the present study were: (1) to add information concerning life history and population differences in two more populations of S. undulatus, and (2) to evaluate current theory, particularly the role of resource availability, concerning evolution of life history patterns and population phenomena in light of the empirically obtained data. MATERIALS AND METHODS The two subspecies studied were S. undulatus consobrinus and S. u. tristichus. Detailed taxonomic descriptions of these two subspecies are given in Cole (1963). Males of both subspecies have a blue patch on each side of the belly and the throat. Female S. u. consobrinus lack blue belly patches, whereas female S. u. tristichus have blue belly patches which tend to be lighter than those of the male. S. u. consobrinus is the larger of the two subspecies and males tend to be smaller than females in both. Both subspecies were studied where they seemed most abundant in southwestern New Mexico. S. u. consobrinus was studied in a desert1 Present address: Department of Environmental Health, Kettering Laboratory, University of Cincinnati Medical Center, Cincinnati, Ohio 45267.