The Advantages of Ectothermy for Tetrapods

Abstract

The way of life of amphibians and reptiles, in contrast to that of birds and mammals, is based on low energy flow. Many of the morphological and physiological characteristics of ectothermal tetrapods that are normally considered to be primitive are in fact adaptations that facilitate a life of low energy demand. Their modest energy requirements allow amphibians and reptiles to exploit various adaptive zones unavailable to birds and mammals. Small body size is the most important of these; 80% of all lizard species and 90% of salamanders have adult body masses less than those of small birds and mammals. An elongate body form, a widespread and successful morphotype among amphibians and reptiles, is energetically unfeasible for endotherms. Amphibians and reptiles also are better suited than birds and mammals to ecological situations characterized by periodic shortages of food, water, or oxygen. At the ecosystem level, the most important consequence of the low energy requirements of amphibians and reptiles is their efficiency of biomass production, which greatly exceeds that of birds and mammals. Their secondary production makes amphibians and reptiles as important as birds or mammals in terrestrial ecosystems.