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First published online April 26, 2005
Journal of Experimental Biology 208, 1717-1730 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01556

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Body size, energy metabolism and lifespan

John R. Speakman

Aberdeen Centre for Energy regulation and Obesity (ACERO), School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ, Scotland, UK and ACERO, Division of Energy Balance and Obesity, Rowett Research Institute, Bucksburn, Aberdeen, AB21 9SB, Scotland, UK

View larger version (38K): [in a new window]   Fig. 1. Resting (basal) metabolic rates (RMR; logeRMR in kJ day-1) of 639 mammals (A) and 381 birds (D) as a function of body mass (Mb, in g). [Least-squares fit equations: mammals, logeBMR=0.781+0.677logeMb, F=6605.89, P<0.001, r2=0.915, RMA gradient=0.708; birds, logeBMR=1.224+0.671logeMb, F=8574.1, P<0.001, r2=0.958, RMA gradient=0.685.] Lifespans (years) of 249 mammals (B) and 164 birds (E) as a function of body mass. [Least-squares fit equations: mammals, logelifespan=0.85+0.209logeMb, F=157.66, P<0.001, r2=0.390, RMA gradient=0.334; birds, logelifespan=1.514+0.216logeMb, F=134.12, P<0.001, r2=0.458, RMA gradient=0.319] and lifetime expenditure of basal energy per gram of body tissue (kJ g-1 life-1) plotted against Mb (g) for 240 mammals - excluding 9 bat species (C) and 141 birds (F) [least-squares fit equations: mammals, loge(lifetime expenditure per gram)=7.268-0.0734logeMb, F=17.97, P<0.001, r2=0.07, RMA gradient=-0.278; birds, loge(lifetime expenditure per gram)= 8.635-0.109logeMb, F=23.28, P<0.001, r2=0.126, RMA gradient= -0.307].

View larger version (16K): [in a new window]   Fig. 2. Histograms of loge[lifetime expenditures of energy (kJ) per gram of tissue] for (A) mammals (N=249) and (B) birds (N=164).

View larger version (29K): [in a new window]   Fig. 3. Residual loge(lifespan in years) plotted against residual loge(basal metabolism in kJ day-1) for (A) mammals (N=249) and (B) birds (N=164). See text for statistics.

View larger version (15K): [in a new window]   Fig. 4. Loge(daily energy expenditure in kJ day-1) measured using the doubly-labelled water (DLW) technique for free-living animals as a function of logeMb (in g) for (A) 73 small mammals and (B) 90 birds. See text for statistics.

View larger version (15K): [in a new window]   Fig. 5. Lifetime expenditure of energy per gram of body tissue plotted against logeMb for (A) mammals and (B) birds. See text for statistics.

View larger version (21K): [in a new window]   Fig. 6. Residual loge(lifetime expenditure of energy per gram of body tissue) plotted against ambient temperature at which the measurement was made for small mammals.

View larger version (17K): [in a new window]   Fig. 7. Residual logelifespan (years) plotted against residual loge(daily energy expenditure in kJ day-1) measured using the doubly-labelled water method for (A) mammals and (B) birds. See text for statistics.