Interactions between the Environment and Ectothermy and Herbivory in Reptiles

Herbivorous reptiles are a comparatively rare group of animals, likely in part because of constraints resulting from interactions between ectothermy and herbivory. Herbivorous lizards, as a group, are characterized by a unique set of morphological, anatomical, and physiological properties. Additionally, most herbivorous lizards are found in (and perhaps partially confined to) the tropics. The most northerly distributed herbivorous lizards, the chuckwalla (Sauromalus obsesus) and the desert iguana (Dipsosaurus dorsalis), occur only in very hot regions of the desert southwestern United States. Herbivorous lizards digest their food much less efficiently than nonherbivorous lizards, and digestive efficiency is affected little by body temperature. However, the rate at which food passes through the gut is affected by body temperature in chuckwallas; specifically, food passes through the gut more slowly at lower body temperatures. Throughout the activity season, free-ranging chuckwallas exploit microhabitats allowing them to have high and constant body temperatures for the maximum amount of time during the day. The inefficiency with which chuckwallas extract energy from food may partially explain why this species occurs in hot desert climates. Indeed, this inefficiency may help to explain, inpart, why all herbivorous lizards in the Western Hemisphere occur in warm climates.