THE EFFECTS OF CONSUMPTION RATE AND TEMPERATURE ON APPARENT DIGESTIBILITY COEFFICIENT, URATE PRODUCTION, METABOLIZABLE ENERGY COEFFICIENT AND PASSAGE TIME IN CANYON LIZARDS (SCELOPORUS-MERRIAMI) FROM 2 POPULATIONS

1. Detailed understanding of the factors that influence digestion is r equired for studies of ecological energetics and individual-based popu lation modelling. With feeding trials, we quantified the effects of te mperature, population of origin, lizard mass and consumption rate on a pparent digestibility coefficient (ADC), urate production, metabolizab le energy coefficient (MEC), and passage time in canyon lizards (Scelo porus merriami) from two populations. 2. ADC was insensitive to temper ature, averaged 0.90 and was significantly affected by consumption rat e only. 3. As expected, urate production was significantly affected by consumption rate, lizard mass and temperature. 4. MEC was significant ly affected by consumption rate, temperature and population of origin. 5. Total passage time of marked food items was lowest at 34-degrees-C and significantly increased with increase or decrease in temperature. 6. We present linear regression models describing ADC, urate producti on and MEC in lizards from these populations. 7. Highest rates of ener gy extraction were achieved at 34-degrees-C which is the average field active body temperature of these lizards. 8. We suggest that the ecol ogical relevance of studies concerned with environmental effects on en ergy extraction rate could be enhanced by integrated study of the comp lete digestive process and by shifting focus from ADC to MEC.