A heat transfer analysis of animals: Unifying concepts and the application of metabolism chamber data to field ecology

Abstract

This paper presents a heat transfer analysis of animals which lies between detailed thermal energy budget analysis and the simplified “Newton's Law of cooling” approach. The analysis considers the animal to be composed of two or three thermal layers. Heat transfer by conduction, convection, and thermal radiation are included separately in linearized form. Solar and thermal radiation from the environment and heat production and loss by metabolism and evaporation are included as rates. The solution for body temperature, T b , is arranged into three parameters: (1) The operative environmental temperature, T e , the effective temperature of the environment for a specific animal, combining conduction, convection, and radiation; (2) the overall thermal conductance, K 0, giving the thermal insulation of the animal; (3) the effective dry metabolic heat production, M∗, the algebraic sum of the metabolic heat production and evaporative cooling, corrected for the partitioning of evaporative cooling between the body core and the environment. For T b constant, T e , and K 0 are combined into a fourth parameter, the standard operative environmental temperature, T es , This parameter is a measure of the value of M∗ required to maintain T b constant, and allows the sensible thermal stress of different environments (e.g. a metabolism chamber and an outdoor habitat) to be compared. The parameters T e , K 0, and M∗ are functionally equivalent to the corresponding parameters in “Newton's Law”. However, this should not be construed to justify the use of “Newton's Law”, since the parameters are not measured correctly by traditional procedures. However, it is possible to make direct measurements of T e , K 0, T es , and M∗ with taxidermic models of the animal. These direct measurements allow a simplified approach to many descriptive problems in thermal physiology and ecology, while obtaining results which may be related to detailed energy budget analysis.