Constructing nutrient budgets

We present a formalised, yet flexible, scheme for classifying and symbolising the components of nutrient budgets. The scheme distinguishes hierarchically both among components of the ingesta and among the various sinks to which they are allocated. The primary terms in the budget are distinguished according to either methodological criteria (whether in a given time period they are retained by the animal or dissociated from the body) or functional criteria (whether they contribute to fitness). In both methodological and functional classifications, the primary terms of the budget may be progressively expanded to represent with increasing resolution nutrient allocation. The interplay between the various components of the ingesta and their subsequent allocation may be considered simultaneously using a two-dimensional nutritional matrix.