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 required for studies of ecological energetics and individual-based population modelling. With feeding trials, we quantified the effects of temperature, population of origin, lizard mass and consumption rate on apparent digestibility coefficient (ADC), urate production, metabolizable energy coefficient (MEC), and passage time in canyon lizards (Sceloporus merriami) from two populations. 2. ADC was insensitive to temperature, averaged 0.90 and was significantly affected by consumption rate only. 3. As expected, urate production was significantly affected by consumption rate, lizard mass and temperature. 4. MEC was significantly 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 production and MEC in lizards from these populations. 7. Highest rates of energy extraction were achieved at 34-degrees-C which is the average field active body temperature of these lizards. 8. We suggest that the ecological relevance of studies concerned with environmental effects on energy extraction rate could be enhanced by integrated study of the complete digestive process and by shifting focus from ADC to MEC.