a test of some hypotheses concerning life history evolution. Journal of Evolutionary Biology 11:329-364.
We analyze, with an augmented data base, patterns
of covariation of the three primary demographic parameters (age at maturity,
fecundity, 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 framework
of recent theories on life history evolution (Ferrière and Clobert
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 phylogenetically based statistical
method (independent contrasts), the allometric (log-log) relationship of
fecundity (and of clutch size) in relation to snout-vent length was found
to differ significantly between the two major clades of extant lizards,
Iguania (43 species in our data set) and Scleroglossa (47 species). We
therefore emphasize analyses done separately for the two clades. Without
removing correlations with body size, the relationships between fecundity
and survival, and between fecundity and age at maturity, were also found
to differ between clades, which differs from Charnov's (1993) predictions.
When correlations with body size were removed statistically, however, the
two clades did not differ significantly in these relationships. In a principal
components 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
(from log-log regressions on snout-vent length), the first axis explained
66-68% of the variation and was clearly interpretable as the classical
"slow-fast" continuum, which has been described in birds and mammals. The
PCA of residuals did not provide clear evidence of additional significant
patterns of covariation. However, the rate of evolution of mortality (size-corrected),
but not of fecundity or age at maturity, differed significantly between
clades. Furthermore, fecundity and age at maturity, both corrected for
variation in adult mortality (in addition to body size), were still significantly
related, indicating the existence of other patterns of variation in these
life history traits. In other words, the ratios between age at maturity
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 variable.
This result contradicts the prediction of Charnov (1993), and suggests
the existence of other directions of evolution in these life history traits.