Fig. 3. The regression line for mass-specific rate of oxygen consumption (s_O2) plotted against heart rate (fH) for seven marine iguanas from Santa Cruz Island, Galapagos, at 36 °C (see Fig. 2) together with the 95 % prediction intervals when s_O2 is estimated from four measurements of fH from four animals. Also included are the values (mean ± S.D.) for s_O2 and fH from four marine iguanas from the island of Santa Fé, Galapagos, during the pre-exercise period (filled circle) and at maximum exercise (open circle) at 36 °C.