Fig. 5. The interaction of ATP turnover rate, diffusion distance and the effectiveness factor (), which is the ratio of the reaction rate in the presence of diffusion to the rate if diffusion were not limiting. The surface was generated from a Loess fit to output from a simplified reaction–diffusion model with linear expressions for ATP production (mitochondria), ATP consumption (ATPases) and diffusion (see text for additional details). The symbols represent the positions on the surface of a variety of anaerobic (white) and aerobic (red) muscle fibers from insects (bee flight muscle) (diamonds), crustaceans (circles), fishes (squares), amphibians (frog lumbrical muscle) (inverted triangle), reptiles (including rattlesnake tailshaker muscle) (crosses), bird (hummingbird flight muscle) (triangle), and mammals (pentagons). The white lines are developmental trajectories from individual species for white muscle fibers that grow hypertrophically (muscles are, in order from low to high ATP turnover rate: blue crab light levator, black sea bass white epaxial muscle, pink shrimp abdominal flexor and grass shrimp abdominal flexor). The black arrow indicates the impact of subdividing the large aerobic fibers of blue crabs, which greatly reduces the intracellular diffusion distances and alleviates diffusion limitation associated with the hypothetical, non-subdivided case (value with a low ) (see text for additional details). Diffusion distances were taken from direct measurements or calculated as in Tyler and Sidell (Tyler and Sidell, 1984) from the mitochondrial volume density and mitochondrial surface density [the latter was calculated assuming a mitochondrial surface area to volume ratio of 6 if not directly measured (Tyler and Sidell, 1984)]. ATP turnover rates per volume of muscle fiber were determined from direct measurements of O₂ consumption in tissue, isolated fibers, or isolated mitochondria assuming 22.4 l O₂ mol^–1 O₂, an ATP/O₂ ratio of 6, and an intracellular water content that was 70% of wet mass. For cases where measurements of O₂ consumption were unavailable, ATP turnover rate was estimated from mitochondrial volume density assuming a sustainable rate of O₂ consumption of 3 ml min^–1 cm^–3 of mitochondrial volume [(Schwerzmann et al., 1989); this value was not applied to mitochondria with known high cristae surface densities]. Data are from the published literature (Tyler and Sidell, 1984; Andersen and Saltin, 1985; Egginton and Sidell, 1989; Schwerzmann et al., 1989; Stokes and Josephson, 1992; Curtin et al., 1997; Conley and Lindstedt, 1998; Johnston et al., 1998; Suarez, 1998; Egginton et al., 2000; Vicini and Kushmerick, 2000; Kanatous et al., 2002; Boyle et al., 2003; Kindig et al., 2003; Johnson et al., 2004; Stary et al., 2004; Kinsey et al., 2005; Hardy et al., 2006; Nyack et al., 2007) and personal observations (S.T.K., unpublished results). In studies of ectotherms from different temperature regimes, only data from the warm acclimated or adapted groups were included.