8. Figures
Figure 1. Graphical model of the expected relationship between the metabolic scaling slope (b ) and the metabolic level (L , the mass-specific metabolic rate at the geometric mass-midpoint of the scaling regression), according to the ‘Metabolic-Level Boundaries Hypothesis’ (Glazier 2010, 2014). Over the range of metabolic states, bvaries with L following a convex relation viewed from below within the limits set by volume-related (V ~m1 ) and surface-area related (SA ~ m2/3 ) resource demand, denoted here by dashed horizontal lines. In cold temperatures (deep blue), the energy demand of resting organisms is low and sufficiently met by SA-related processes (minimal L ), so body maintenance dictates metabolic rate (b ≈ 1). As temperature rises (from blue to red), resting metabolic rates relatively increase and so L , becoming more influenced by fluxes through exchange surfaces, which causes b to approach 2/3. Activity, conversely, leads b to increase and ultimately approach 1 during strenuous exercise (maximalL ), since metabolism is driven temporarily by demands of muscular mass, proportional to body mass (m1 ) when growth is isomorphic. Note that L increases here exponentially (or linearly if log-transformed) with temperature and activity. The shape of the relationship between b and log L will depend on the predominant influence of each contributing process under specific temperatures and activity levels.