Fig. 1. Simplified model of thermal tolerance and eurythermal temperature adaptation in animals (modified after Pörtner, 2001a) considering (A) contributions to metabolic heat production () by oxygen consumption (_O2) and anaerobic metabolism (_anae). The model is based predominantly on data for water-breathers. Mechanisms shifting the respective tolerance thresholds include a change in overall mitochondrial functional capacity (B), which causes a shift in both lower (I) and upper (II) pejus temperature (T_p, the onset of a decrease in aerobic scope) and critical temperature (T_c, the onset of anaerobic metabolism). Reductions in oxygen demand and anaerobic heat production are expected to result from a decrease in mitochondrial densities and capacities during warming (indicated by arrows in A).

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