Balancing nutrients, water and heat in the face of environmental change: a thermodynamic niche framework.

Models of the regulatory behaviour of organisms are fundamental to a strong physiologically-based understanding of species' responses to global environmental change. Biophysical models of heat and water exchange in organisms (biophysical ecology) and nutritionally-explicit models for understanding feeding behaviour and its fitness consequences (the Geometric Framework of nutrition, GF) are providing such an underpinning. However, temperature, water and nutrition interact in fundamental ways in influencing the responses of the organism to their environment, and a priority is to develop an integrated approach for conceptualising and measuring these interactions. Ideally, such an approach would be based on a thermodynamically-formalized energy and mass budgeting approach that is sparsely parameterised and sufficiently general to apply across a range of situations and organisms. Here we illustrate how mass-balance aspects of Dynamic Energy Budget theory can be applied to obtain first-principles estimates of fluxes of O