Demography and population dynamics of the lacertid lizard Podarcis bocagei in north-west Spain

Abstract

The demography and life-history traits of a population of the lacertid lizard Podarcis bocagei in north-west Spain were investigated. Most of the conclusions presented are based on mark–recapture studies carried out over a 2-year period. Reproductive characteristics are similar to those reported for other temperate-climate lacertids. Clutch size, egg size and hatchling size (snout–vent length, SVL) are all positively correlated with the mother's SVL. Only large females lay more than one clutch per year. Growth rate is highest in young animals and declines gradually with age. In both sexes, sexual maturity is reached between the ages of 1 and 2 years. Again in both sexes, the probability of survival was fairly constant over the lifespan. Considering the study period as a whole, there was no significant between-sex difference in survival probability. Among adults, the probability of survival was higher in winter than during other periods, but the differences were not statistically significant. The individuals of the study population are sedentary, making only short movements even when periods of up to 2 years are considered (the mean distance moved between marking and recapturing 18–24 months later was 15.7 m, maximum 45.6 m). On average, immature individuals move further than adults, and adult males move further than adult females. Estimated population density (all individuals) dropped from 1574 ha^-1 during the winter of 1989/90 to 1327 ha^-1 during the winter of 1990/91. The decline in population density over the study period was also reflected in the estimated net replacement rate for the population (0.85, i.e. considerably less than one), and is probably attributable to colonization of the study site by plants (reducing suitability as a habitat for P. bocagei). Estimated mean generation time was 2.09 years.