Figure 4. Comparison of the intraspecific metabolic scaling with body mass in ectothermic vertebrates. Left panels show scaling regressions performed at various temperatures in inactive individuals of water- (A ) and air-breathers (B ). Right panels show regressions for individuals under different activity levels of water- (C ) and air-breathers (D ), adjusted to the approximate mean temperature of each dataset (Appendix S8). Dashed lines denote the upper and lower metabolic scaling slopes (b ) as metabolic level (L ) increases with temperature (A, B) or activity (C, D). These slopes were predicted through model estimates, by using values of the minimal and maximal L values calculated at the geometric mass-midpoint of the range reported for water- and air-breathing species in each dataset. B and C show mean b and L values, as the estimated change in b overlapped 0, indicating no overall effect of L . The explanation proposed here for these changes in b is shown on each panel.