Body mass scaling of passive oxygen diffusion in endotherms and ectotherms.
The area and thickness of respiratory surfaces, and the constraints they impose on passive oxygen diffusion, have been linked to differences in oxygen consumption rates and/or aerobic activity levels in vertebrates. However, it remains unclear how respiratory surfaces and associated diffusion rates vary with body mass across vertebrates, particularly in relation to the body mass scaling of oxygen consumption rates. Here we address these issues by first quantifying the body mass dependence of respiratory surface area and respiratory barrier thickness for a diversity of endotherms (birds and mammals) and ectotherms (fishes, amphibians, and reptiles). Based on these findings, we then use Fick's law to predict the body mass scaling of oxygen diffusion for each group. Finally, we compare the predicted body mass dependence of oxygen diffusion to that of oxygen consumption in endotherms and ectotherms. We find that the slopes and intercepts of the relationships describing the body mass dependence of passive oxygen diffusion in these two groups are statistically indistinguishable from those describing the body mass dependence of oxygen consumption. Thus, the area and thickness of respiratory surfaces combine to match oxygen diffusion capacity to oxygen consumption rates in both air- and water-breathing vertebrates. In particular, the substantially lower oxygen consumption rates of ectotherms of a given body mass relative to those of endotherms correspond to differences in oxygen diffusion capacity. These results provide insights into the long-standing effort to understand the structural attributes of organisms that underlie the body mass scaling of oxygen consumption.
Department of Biology, University of Florida, Gainesville, FL 32611; gillooly@ufl.edu.
James F
JF
Gillooly
Department of Biology, University of Florida, Gainesville, FL 32611; Florida Museum of Natural History, University of Florida, Gainesville, FL 32611;
Juan Pablo
JP
Gomez
Florida Museum of Natural History, University of Florida, Gainesville, FL 32611;
Evgeny V
EV
Mavrodiev
Department of Agricultural and Biological Engineering, University of Florida, Gainesville, FL 32611.
Yue
Y
Rong
Department of Agricultural and Biological Engineering, University of Florida, Gainesville, FL 32611.
Eric S
ES
McLamore
D000818:Animals; D001481:Basal Metabolism / Q000502:physiology; D015992:Body Mass Index; D001833:Body Temperature Regulation / Q000502:physiology; D001835:Body Weight / Q000502:physiology*; D003198:Computer Simulation; D004058:Diffusion; D005399:Fishes; D006801:Humans; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D013045:Species Specificity
D010100:Oxygen
allometry; metabolic theory; metabolism; oxygen consumption; respiration rate