Growth and mortality in a field population of Amphibolurus lizards exposed to seasonal cold and aridity



The demography of a discrete population of Amphibolurus ornatus lizards in Western Australia was studied over a period of four years. Large differences in the rate of growth of individuals from the same cohort were observed during each year of the study and each animal could be classified as maturing at one, two or three years of age. Fast- and slow growing individuals were shown to suffer differential mortality during seasonal stresses with fast growers being cold hardy and drought sensitive whereas slow-growers were cold sensitive but drought resistant. The potential longevity of fast- and slow-growing animals appears to be identical but the survival of animals in the field depends markedly upon the incidence of climatic extremes, slow growers tending to live longer than fast growers in the study area. Changes that were observed in the size and age structure of the breeding population during the period of study can be interpreted in terms of the weather conditions experienced by the population over this period. The significance of the variability in individual growth rates of Amphibolurus ornutus for the persistence of the study population is discussed.