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Cooperation in contention : the evolution of ASEAN norms Poole, Avery Dorothy Howard

Abstract

There are a number of methods commonly used to estimate metabolic rate in animals, one of which is the Heart Rate Method. Heart rate (f[sub H]) can theoretically be used as a direct proxy for O₂ consumption (V[sub O]) according to Fick's equation (V[sub O] = f[sub H] x O₂ pulse) as long as the O₂ pulse varies in a predictable manner. The benefit of this method is that heart rate is easily monitored both in the lab and in the field, is sensitive to short-term changes in activity, and can be monitored continuously on the order of weeks or months. Studies have confirmed that in some birds, mammals, and at least one species of reptile, the accuracy of this method is at least as great as that of the doubly-labelled water method. My goal was to determine if heart rate can be used as a reliable estimate of metabolic rate in tegu lizards. To this end, f[sub H] and V[sub O] were measured simultaneously in fasting lizards at 17°C, 27°C and 37°C, and in digesting lizards at 37°C. Regression analysis showed that, at any given temperature or digestive state, the relationship between f[sub H] and V[sub O] was highly variable between individuals (as indicated by different slopes and intercepts) as well as within individuals (as indicated by low r² values). Regression analysis on data pooled within each treatment failed to account for this variability. However, regression analysis of the dataset in its entirety accounted for 740/0 of the variability. The equation which best described the relationship in unstressed animals was lnsV[sub O] = —3.441 + 0.679 InF[sub R]. Predictions of total metabolic rate calculated from this general calibration equation were typically more accurate than predictions based on the Time Energy Budget method.

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