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.