Integrating nutrition: a geometrical approach

We present and illustrate using data from insects an integrative approach t o modelling animal nutrition. This framework enables the unification within simple geometrical models of several nutritionally relevant measures. Thes e include: the optimal balance and amounts of nutrients required to be inge sted and allocated to growth by an animal over a given time period (the int ake and growth targets, respectively); the animal's current state in relati on to these requirements; available foods and the consequences for the anim al's state of ingesting them; the amounts of ingested nutrients that are re tained and eliminated; and animal performance. Data are presented on intake targets in insects, illustrating how they change over various time-scales (physiological, developmental, and evolutionary). Most importantly, the geo metrical approach enables a clear description to be made of the trade-offs reached by animals in regulating their nutritional balance. Animals given a nutritionally balanced food, or two or more imbalanced but complementary f oods, can satisfy their nutrient requirements. However, those eating non-co mplementary imbalanced foods must reach a suitable compromise between over- ingesting some nutrients and under-ingesting others. Data are presented com paring the rules of compromise for protein and carbohydrate ingestion in gr ass-feeding (Locusta migratoria) and polyphagous (Schistocerca gregaria) lo custs.