Energy Utilization by Free‐Ranging Sceloporus Virgatus Lizards

Abstract

Seasonal and sexual differences in daily energy allocation were evaluated for the striped plateau lizard (Sceloporus virgatus, Sauria: Iguanidae) from field measurements of metabolic rates (doubly labeled water), time—activity budgets, body temperatures, and energy storage rates, along with laboratory measurements of resting metabolism (gas exchange) and food utilization efficiency. In spring, males had higher field metabolic rates (FMRs) than females, but females consumed food factor while abroad and used the extra energy for producing eggs. Females were abroad about half as long as males (3.6 vs. 7.6 h/d) but an estimate of their energy metabolism while abroad was much higher than that of males (8.3 vs. 3.6 times resting metabolic rate). Males did not eat enough food to satisfy their energy and they lost body mass in spring. During summer, both sexes maintained constant body masses and steady—state energy budgets, but females had much higher FMRs and feeding rates than mules because females were abroad and active longer than males. Daily energy expenditure was positively correlated with duration of daily activity period. A lizard that was active 8 h/d had an FMR about 8 times higher than if it had remained inactive in a retreat all day. Thus S. virgatus can change its daily cost of living by nearly an order of magnitude by varying the time it spends abroad. Field behavior patterns are consistent with the hypothesis that these lizards regulate their activity in a manner that enhances survival and reproduction.