Holistic system analysis of the energetic power and efficiency of animal production

Major features of living systems are the rates (power) and ratios (efficiency) of their energy uptake and use, whose relationships are not entirely predictable from those seen in nonliving physical systems. Although the energetic power and efficiency of production (growth and reproduction) are known to respond to differences in ration level, diet, and other intrinsic and extrinsic factors, why these responses vary considerably among animals is little understood and often ignored in theoretical models. In this exploratory study I show that a holistic analysis of how the different responses of the efficiencies of resource uptake and use systems to variation in food levels and associated rates of energy flow (power) helps one predict the ration-dependent efficiency of conversion of ingested energy into growth and reproduction. When the relative influence of the efficiency of assimilation (resource supply) predominates (as in many herbivores), the efficiency of converting ingested energy into production tends to vary negatively with ration level and production power, whereas when the relative influence of the efficiency of converting assimilated energy into biological tissues (resource use) predominates (as in carnivores), the ingestive production efficiency tends to vary positively with ration level and production power. I also extend this analysis by showing how studies at multiple hierarchical levels of biological organization, from cells to ecosystems, may improve our understanding of the covariation of production efficiency with ration level or overall rate of energy flow (power). A new comprehensive theory of the power and efficiency of living systems is advocated.