THE EVOLUTION OF DEMOGRAPHIC TACTICS IN LIZARDS - A TEST OF SOME HYPOTHESES CONCERNING LIFE-HISTORY EVOLUTION

We analyze, with an augmented data base, patterns of covariation of th e three primary demographic parameters (age at maturity, fecundity, ad ult survival, all measured in the same unit of time) in lizards. This also constitutes a first attempt to use all three of these parameters for this group of species. We attempt to place these analyses in the f ramework of recent theories on life history evolution (Ferriere and Cl obert, 1992; Charnov, 1993). Life history data were collected from the literature and from our original work, and a composite phylogeny was assembled, based on a variety of published sources. Using a phylogenet ically based statistical method (independent contrasts), the allometri c (log-log) relationship of fecundity (and of clutch size) in relation to snout-vent length was found to differ significantly between the tw o major clades of extant lizards, Iguania (43 species in our data set) and Scleroglossa (47 species). We therefore emphasize analyses done s eparately for the two clades. Without removing correlations with body size, the relationships between fecundity and survival, and between fe cundity and age at maturity, were also found to differ between clades, which differs from Charnov's (1993) predictions. When correlations wi th body size were removed statistically, however, the two clades did n ot differ significantly in these relationships. In a principal compone nts analysis (PCA) of the three demographic variables plus snout-vent length, the first axis explained the majority (53-57%) of variation in both clades, while the second axis explained 27-31% of the variation and loaded mainly on fecundity. In a PCA of size-adjusted demographic variables residuals (from log-log regressions on snout-vent length), t he first axis explained 66-68% of the variation and was clearly interp retable as the classical ''slow-fast'' continuum, which has been descr ibed in birds and mammals. The PCA of residuals did not provide clear evidence of additional significant patterns of covariation. However, t he rate of evolution of mortality (size-corrected), but not of fecundi ty or age at maturity, differed significantly between clades. Furtherm ore, fecundity and age at maturity, both corrected for variation in ad ult mortality (in addition to body size), were still significantly rel ated, indicating the existence of other patterns of variation in these life history traits. In other words, the ratios between age at maturi ty and adult mortality, or between fecundity and adult mortality, were not found to be invariant, because the variation not accounted for by these ratios was significantly associated with variation in another v ariable. This result contradicts the prediction of Charnov (1993), and suggests the existence of other directions of evolution in these life history traits.