METABOLIC AND WATER-FLUX RATES OF FREE-RANGING TROPICAL LIZARDS SCELOPORUS-VARIABILIS

Daily activity periods, thermal profiles, and stomach contents of Sceloporus variabilis (7.7 g mean body mass) were studied at Bastonal (1,000 m elevation) and Monte Pio (45 m elevation) in southern Veracruz, Mexico. Metabolic rates of free-ranging lizards were measured during late summer using doubly labeled water and were compared to values for temperate sceloporine lizards. Lizards were active from about 0800 hours to 1800 hours. Mean body temperatures of lizards averaged 28.9-degrees-C at Bastonal and 32.4-degrees-C at Monte Pio. Water-influx rates averaged 132 and 108 mL CO2 (kg d)-1 at Bastonal and Monte Pio, respectively. Metabolic rates measured in the field were not different at the two sites and when combined averaged 0.40 mL (g h)-1 or 240 J (g d)-1. Metabolic rates averaged about 6.5 times estimated resting metabolic rate, and activity metabolism accounted for 73% of total respiration. Water-influx rates of S. variabilis are about 4.5 times higher and field metabolic rates are about 1.6 times higher than similar values reported for temperate sceloporine lizards. The increased metabolic and water-influx rates in S. variabilis are apparently due to a combination of greater availability of food and water, favourable thermal conditions, and a higher level of foraging activity and movements than those of temperate sceloporine lizards.