On the evolutionary physiology of metabolic allometry

Abstract

All organisms rely on metabolisma complex system of biochemical reactions that either release or absorb energyto sustain life. Organisms expend energy to develop, grow, survive and reproduce. The total energy expenditure of an animal, as indicated by their metabolic rate, increases as organisms get larger. Metabolic rate, however, scales disproportionately (allometrically) with body mass, such thaton a gram for gram basissmaller organisms have a higher mass-specific metabolic rate than larger organisms. This observation has puzzled biologists for over 150 years, but progress has been made in the past few decades in explaining the origin and maintenance of metabolic allometry. The scaling relationship between mass and metabolic rate can be observed at different levels of biological organisation including over development (ontogenetic scaling), among individuals of the same developmental stage (static scaling), and among species (interspecific scaling). Importantly, there is variation in the scaling relationship between and within each of these levels and this variation has implications for the way energy flows through organisms and ecosystems, as described by metabolic theories of ecology, and for the evolution of metabolic rate and body size across the tree of life. Existing hypotheses for the variation in metabolic scaling revolve around the idea that there are universal physical constraints on the transport of metabolic inputs and outputs through circulatory networks and across tissue surfaces. The contention is that these physical constraints are I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis and have sought permission from co-authors for any jointly authored works included in the thesis.