Re-examination of the 993/4-law:: of Metabolism

We examine the scaling law BJMa which connects organismal resting metabolic rate B with organismal mass M, where a is commonly held to be 3/4. Since simple dimensional analysis suggests a"2/3, we consider this to be a null hypothesis testable by empirical studies. We re-analyse data sets for mammals and birds compiled by Heusner, Bennett and Harvey, Bartels, Hemmingsen, Brody, and Kleiber, and "nd little evidence for rejecting a"2/3 in favor of a"3/4. For mammals, we "nd a possible breakdown in scaling for larger masses re#ected in a systematic increase in a. We also review theoretical justi"cations of a"3/4 based on dimensional analysis, nutrient-supply networks, and four-dimensional biology. We "nd that present theories for a"3/4 require assumptions that render them unconvincing for rejecting the null hypothesis that a"2/3. ( 2001 Academic Press