A new flexible model for maintenance and feeding expenses that improves description of individual growth in insects

Metabolic theories in ecology interpret ecological patterns at different levels through the lens of metabolism, typically applying allometric scaling to describe energy use. This requires a sound theory for individual metabolism. Common mechanistic growth models, such as ‘von Bertalanffy’, ‘dynamic energy budgets’ and the ‘ontogenetic growth model’ lack some potentially important aspects, especially regarding regulation of somatic maintenance. We develop a model for ontogenetic growth of animals, applicable to ad libitum and food limited conditions, based on an energy balance that expresses growth as the net result of assimilation and metabolic costs for maintenance, feeding and food processing. The most important contribution is the division of maintenance into a ‘non-negotiable’ and a ‘negotiable’ part, potentially resulting in hyperallometric scaling of maintenance and lowered maintenance under food restriction. Furthermore, the model may account for effects of body composition and type of growth at the cellular level, and is unique in its ability to capture the unusual pattern of increased growth rate under food restriction observed in some insects. Our model is evaluated by comparing its fit to data for house crickets with that of common mechanistic growth models. Unlike the latter, our model was able to capture the empirical growth patterns.