Comparative ecology of two lizards (Sceloporus variabilis and Sceloporus undulatus) in an area of sympatry

Vita.An ecological study of sympatric populations of Sceloporus variabilis and S. undulates was conducted from February 1975 until February 1976. The study area was located in Uvalde County, Texas in an ecotone between the South Texas Plains and the Edwards Plateau. Food habits were found to be quite similar in both species, with dietary changes occurring during the growth of the lizards. Males and females of both species were sexually mature by their first spring. Females of both species produced two clutches per year, averaging 4.72 eggs per clutch in S. variabilis and 8.0 eggs per clutch in S. undulates. Sceloporus variabilis deposited eggs in late March and June, with hatchlings appearing from early June until late July. Maximum fat body volumes for both species occurred in late fall, with females depositing larger volumes of fat than males. A rapid drop in fat body volumes corresponded to the development of the first clutch of eggs produced in the spring. With the exception of the summer months, males of both species contained mature sperm throughout most of the year, and the period of minimum testes size corresponded with the absence of mature sperm. Densities of adult lizards during the reproductive season were 7.3 per hectare for S. variabilis and 6.9 per hectare for S. undulates Although the clutch size of S. undulates was larger, its clutch success was less than that of S. variabilis. There was almost a complete population turnover for both species during a year's time.