DEMOGRAPHY OF AN URBAN POPULATION OF THE TEXAS HORNED LIZARD (PHRYNOSOMA CORNUTUM) IN CENTRAL OKLAHOMA

The dynamics of reptile populations in urban landscapes are poorly understood. We studied demography of an urban population of the Texas horned lizard (Phrynosoma cornutum), a species that apparently declines in abundance following urban development but may persist in localized areas. We located and captured lizards within an urban reserve at Tinker Air Force Base, Oklahoma, from June 2003 to October 2005. Lizards were monitored using radiotelemetry, and data were collected on morphometrics, survival, and reproduction. These data were applied to a life-table analysis that estimated the hatchling survival rate necessary to maintain a stable population. Females were larger than males in adult and juvenile cohorts. Mark-recapture sessions resulted in estimates (±1 SE) of 53 ± 11 individuals in the population and a density of 5.00 ± 1.04 lizards/ha. Annual rates of survival were estimated to be 0.59–0.70 for adult lizards and 0.45 for juvenile lizards. Mean (±1 SE) clutch size was 17.4 ± 0.8 eggs, incubation periods ranged from 49 to 68 days, and 60% of nests survived to hatching. Assuming a single clutch per year, fecundity of adult females was 5.22 female hatchlings/female/year. From application of Euler's equation, the hatchling survival rate needed for population stability ranged from 0.19 to 0.25. Relative to other, more southerly populations of P. cornutum, our study population had higher survival but lower reproductive rates. Reduced reproduction was likely due to latitudinal trends associated with body size, but we could not separate confounded influences of urban environment and latitude on survival. Relative to other phrynosomatine lizards, Texas horned lizards in our study population were characterized by high survival, moderate reproductive output, and delayed maturation.