METABOLISM OF A DESERT LIZARD - THE EFFECTS OF MASS, SEX, POPULATION OF ORIGIN, TEMPERATURE, TIME OF DAY, AND FEEDING ON OXYGEN-CONSUMPTION OF SCELOPORUS-MERRIAMI

Characterization of metabolic rate is critical to constructing daily and seasonal energy budgets, constructing models of individuals for use in individual-based modeling, understanding patterns of resource allocation, and understanding within- and among-population variation in life-history phenotypes. We investigated the effects of mass, ambient temperature, time of day, sex, population of origin, and feeding on O2 consumption of the canyon lizard, Sceloporus merriami. We observed strong effects of mass and ambient temperature and constructed predictive relationships for O2 consumption on the basis of these variables for scotophase and photophase. These fundamental relationships coupled with existing field body temperature data suggest that lizards from populations exhibiting different daily body temperature profiles may significantly differ in maintenance requirement. We observed strong diel cycles in O2 consumption that were correlated with daily activity. No main effects of sex or population of origin were observed. A significant higher-order interaction involving temperature, time of day, sex, and population of origin suggests that ecologically significant variation in metabolic rate may occur between groups defined by sex and population. A plateau in O2 consumption between 32-degrees and 34-degrees-C was observed during scotophase. This plateau is not easily explained as a mechanism of homeostasis because scotophase body temperatures may often fall below this range. Feeding significantly increased O2 consumption in this species; the magnitude of increase was linearly related to meal size. We estimated the total energetic cost of digestion to be between 2.9% and 4.9% of dietary metabolizable energy content.