We present the state of the art of the development of dynamic energy budget theory, and its expected developments in the near future within the molecular, physiological and ecological domains. The degree of formalization in the set-up of the theory, with its roots in chemistry, physics, thermodynamics, evolution and the consistent application of Occam's razor, is discussed. We place the various contributions in the theme issue within this theoretical setting, and sketch the scope of actual and potential applications.Keywords: dynamic energy budget theory; biology; metabolism; ecology; evolution; energetics
REACHING OUT FOR GENERALITYIn physics, there is a quest for a unified theory. Physical theories have a broad spectrum of application, a strong mathematical background and are subject to numerous empirical tests. By contrast, in biology, mathematical theory has played a secondary role because biology is frequently seen as a science of exceptions and particular cases, with little interest in abstraction and generalization. Exceptions are the research being done in the fields of theoretical biology and mathematical biology. However, theoretical and mathematical biology have frequently been carried out without a concern for empirical testing. When this concern appears, models are of narrow application, reducing their theoretical breadth. The dynamic energy budget (DEB) theory starts from the Dutch tradition of theoretical and mathematical biology, but couples it with a fundamental concern in producing general theory that is subjected to careful empirical testing.DEB theory aims to capture the quantitative aspects of metabolism at the individual level for organisms of all species. It builds on the premise that the mechanisms that are responsible for the organization of metabolism are not species-specific (Kooijman 2001(Kooijman , 2010. This hope for generality is supported by (i) the universality of physics and evolution and (ii) the existence of widespread biological empirical patterns among organisms . Table 1 synthesizes the essential criteria for any general model for the metabolism of individuals. We explore the links between DEB theory and each of the proposed criteria in the following paragraphs. DEB theory is explicitly based on the conservation of mass, isotopes, energy and time, including the inherent degradation of energy associated with all processes. So it complies to criteria 1, table 1.The DEB theory is biologically implicit, so it applies to all species. Species-specific restrictions of DEB models are explained and predicted by the theory (criterion 5, table 1). For example, consider the most important difference between DEB models, the number of reserves (biomass components that fuel metabolism) and structures (biomass components that have maintenance needs) that are delineated. This depends on the degree of coupling of the various substrates an organism needs. Animals feed on other organisms, which couples uptake of the various substrates (proteins, carbohydrates, lipids, nutrients) tightly and ex...