This chapter discusses the mechanistic basis of different processes which together constitute the Dynamic Energy Budget (DEB) model. Further chapters evaluate consequences at the individual level. Tests against experimental data are presented during the discussion to examine the realism of the model formulations, and also to develop a feeling for the numerical behaviour of the model elements. The next chapter presents additional tests that involve combinations of processes. The sequential nature of human language does not do justice to the many interrelationships of the processes. These interrelationships are what makes the DEB model more than just a collection of independent submodels. I have chosen here to follow the fate of food, ending up with production processes. This order fits ‘supply’ systems, but for ‘demand’ systems another order may be more natural. The relationships between the different processes is schematically summarized in Figure 3.1.

The details and logic of the energy flows will be discussed in this chapter; a brief introduction will be given in this introductory section.

Food is ingested by an animal, transformed into faeces and egested. Energy derived from food is taken up via the blood, which has a low capacity for energy but a high transportation rate. Blood exchanges energy with the storage, and delivers energy to somatic and reproductive tissues. A fixed part, k, of the catabolic flux, i.e. the energy delivered by the blood, is used for (somatic) maintenance plus growth, the rest for development and/or reproduction. The decision rule for this fork is called the k-rule.