The Golden Mouse: A Model of Energetic Efficiency

Patterns of energy acquisition and use (i.e., bioenergetics) by mammals have important consequences for the ecology of the individual organism as well as the populations, communities, ecosystems, and landscapes in which they live (Ernest 2005, Grodzinski and Wunder 1975, McNab 1980, 2002). A bioenergetic pathway for a typical mammal is depicted in Figure 8.1 and can be summarized in the form of three equations: (1) I = E + A, where I is ingested energy, E is energy lost by the egestion of nondigestable material in the form of feces, and A is assimilated energy that is available to the organism following digestion and absorption; (2) A = U + M + G + R represents the energy budget of the organism (McNab 2002), where U is energy lost through the excretion of nitrogenous waste products in urine and M, G, and R represent energy allocated for metabolism, growth, and reproduction, respectively; (3) M = h + m + t + a, where h is energy lost to the organism in the form of heat during cellular respiration, m is energy needed for the maintenance of basal metabolic rate, t is energy used for thermoregulation, and a is energy used for activities such as foraging, predator avoidance, and dispersal.