The influence of the cost of growth on ectotherm metabolism

A new model of ectothermic growth and metabolism is proposed. This model differs from most earlier models in representing explicitly the contribution of the “cost of growth” to ectotherm metabolism. It is shown that the cost of growth may constitute between 17 and 29% of the metabolism of an “average” ectotherm population. Furthermore, the metabolism of an “average” growing ectotherm may be between 40 and 79% greater than that of a non-growing ectotherm. As many environmental factors induce changes in metabolic rates of this magnitude, it is suggested that many factors which cause changes in metabolic rates do so indirectly by altering growth rates. In particular, it is suggested that body size, food availability and temperature often indirectly influence metabolic rates through their effects on growth rates, rather than by directly determining metabolic rates as has usually been assumed.