Fig. 2.

The observed body mass dependence of oxygen consumption and the predicted body mass dependence of oxygen diffusion for (A) endotherms at rest (birds and mammals; n = 580) and (B) ectotherms at rest (reptiles, fishes, and amphibians; n = 249). Dashed lines are fitted to the oxygen consumption rate data using PGLS regression (Table 1). Solid lines are the predicted relationships of oxygen diffusion (milliliters of O₂ per hour) to body mass (grams) following Eq. 1. Data and sources are listed in SI Appendix, Appendixes 1–3.