PATTERNS OF SURVIVAL, GROWTH, AND MATURATION IN SNAKES AND LIZARDS

We review published data to determine whether squamate reptiles show a specific series of quantitative relationships among life-history characteristics, as predicted by mathematical models and observed in other vertebrate and invertebrate groups. We focus on growth rates, adult survival rates, and ages at sexual maturation. In general, snakes and lizards show patterns similar to those expected. The body size at maturation is a relatively constant proportion of maximum size, and adult survival rate is proportional to age at maturity. The von Bertalanffy growth constant (K) is positively correlated with the adult instantaneous mortality rate (M) such that the ratio of the two variables is generally close to 1.0. Phylogenetically based analyses show that these results are not artifacts due to phylogenetic conservatism. The constants of proportionality linking age at maturity to rates of mortality are higher than those of endothermic vertebrates but lower than those of previously studied invertebrates. Although snakes differ from lizards in mean values of several life-history traits, the relationships among these variables are usually similar in the two suborders. These analyses show that squamate reptiles exhibit interspecific and intraspecific patterns of growth, survival rate, and maturation that are of the same qualitative (and, often, quantitative) form as those seen in other types of organisms in which growth continues after maturity.