Allometric Patterns in the Ecology of Australian Snakes

Abstract

This paper summarizes published and original data on ecological characteristics of 103 species of Australian snakes, based on dissection of > 22,000 specimens in museum collections. Principal Component Analyses suggest that much of the interspecific variance in ecology is the result of differences in mean adult body sizes. Thus, I examine the degree to which absolute body size is correlated with other ecological variables in interspecific comparisons and investigate interspecific associations between ecological traits after the confounding effect of absolute body size is removed from the analysis. Mean adult body size is significantly correlated with measures of population structure (adult sex ratio), growth trajectories (size at maturation relative to mean adult size, and sexual size dimorphism), mating systems (presence or absence of male-male combat), reproductive biology (offspring size, clutch size, reproductive mode, and reproductive frequency in females), and food habits (proportional composition of major prey types). Phylogenetically based analyses show that some of these interspecific correlations are the result of phylogenetic conservatism, whereas others reflect underlying functional relationships. When these kinds of allometric effects are taken into account, clear patterns in interspecific variation in life-history attributes are revealed. For example, a trade-off is apparent between clutch size and offspring size: species with relatively large clutches produce relatively small offspring. Offspring size is unaffected by shifts in reproductive mode (oviparity/viviparity) but is correlated with the extent of postmaturational growth by females (in species with relatively large offspring, females delay maturation until they reach a large size). The presence or absence of male-male combat in a species affects adult sex ratio in collections (probably via sex biases in catchability), growth trajectories in males, and the degree of sexual size dimorphism.