The application of mass and energy conservation laws in physiologically structured population models of heterotrophic organisms

Rules for energy uptake, and subsequent utilization, form the basis of popu lation dynamics and, therefore, explain the dynamics of the ecosystem struc ture in terms of changes in standing crops and size distributions of indivi duals. Mass fluxes are concomitant with energy hows and delineate functiona l aspects of ecosystems by defining the roles of individuals and population s. The assumption of homeostasis of body components, and an assumption abou t the general structure of energy budgets, imply that mass fluxes can be wr itten as weighted sums of three organizing energy fluxes with the weight co efficients determined by the conservation law of mass. These energy fluxes an assimilation, maintenance and growth, and provide a theoretical underpin ning of the widely applied empirical method of indirect calorimetry, which relates dissipating heat linearly to three mass fluxes: carbon dioxide prod uction, oxygen consumption and N-waste production. A generic approach to th e stoichiometry of population energetics from the perspective of the indivi dual organism is proposed and illustrated for heterotrophic organisms. This approach indicates that mass transformations can be identified by accounti ng for maintenance requirements and overhead costs for the various metaboli c processes at the population level. The theoretical background for couplin g the dynamics of the structure of communities to nutrient cycles, includin g the water balance, as well as explicit expressions for the dissipating he at at the population level are obtained based on the conservation law of en ergy. Specifications of the general theory employ the Dynamic Energy Budget model for individuals. (C) 1999 Academic Press.