Interhabitat Differences in Energy Acquisition and Expenditure in a Lizard

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Abstract
Cnemidophorus hyperythrus, a small (°4—g) teiid lizard, occurs along an elevational thorn scrub–thorn woodland–thorn forest habitat gradient in the cape region of Baja California. We compared body size, daily energy expenditure (DEE, measured with doubly labeled water), relative feeding rate (as reflected by H2O influx rate), behavior, and abundance of this species at two sites along the gradient. At the inland thorn woodland site C. hyperythrus were more abundant (°100 lizards/ha) than at the thorn scrub site near the ocean (°50 lizards/ha). Mean body mass of woodland site lizards was 13% greater than that of scrub lizards. The DEE of the thorn woodland lizards, 330 J°g—1 d—1 , and their H2O influx, 99 mm3°g—1°d—1 , were also higher than the thorn scrub lizards', 219 J°g—1°d—1 and 52 mm3°g—1°d—1. Diets at the two sites were similar. There were no differences between sexes in diet, DEE, or H2O influx. Daily maintenance energy costs were calculated based upon laboratory measures of O2 consumption of resting lizards at a series of temperatures that represented the daily range of body temperatures experienced by lizards in the field. Activity costs (=DEE minus maintenance) were three times higher in the woodland lizards. Behavioral observations showed that the woodland lizards were active most of the day (°9 h/d) whereas scrub lizards were active primarily in the morning (°3.5 h/d). Thus, the higher activity cost, DEE, and feeding rate of woodland lizards can be explained by their longer daily activity period. We suggest casual factors for the difference in daily activity period, and discuss implications of length of daily foraging period for adult body size, population density, and various life history parameters of lizards.