Metabolic scaling, life history, and the equal fitness paradigm

TL;DR

This paper reviews the metabolic theory of ecology's predictions on biological scaling, discusses mixed empirical support, and introduces the Equal Fitness Paradigm as a unifying framework for bioenergetics and life history.

Contribution

It synthesizes existing evidence on metabolic scaling, critiques the theory, and presents the EFP as a comprehensive alternative framework for understanding biological diversity.

Findings

Mixed support for quarter-power scaling exponents.

Natural selection influences scaling patterns across taxa.

The EFP unifies bioenergetics and life history theories.

Abstract

Natural selection has produced an extraordinary diversity of life histories spanning many orders of magnitude in body size, vital rates, and biological times. In general, big and cold organisms grow and reproduce slowly and live long lives; small and warm organisms grow and reproduce quickly and live short lives. The Metabolic Theory of Ecology (MTE) predicts equal and opposite scaling exponents of mass-specific biological rates (e.g., respiration, growth, and reproduction) and times (e.g., development, lifespan, and generation) as a function of size. However, empirical support for these predictions varies depending on trait and taxon. Here I: 1) provide background and mixed support for the quarter-power scaling exponents for life history rates and times predicted by MTE, 2) discuss possible explanations, including effects of natural selection on taxonomic and functional groups, and inadequate data for life history traits, 3) briefly summarize the Equal Fitness Paradigm (EFP) as a unifying theory of bioenergetics, life history and demography that does not depend on any particular allometric scalings, and 4) discuss ramifications of the EFP for other biological phenomena, including physiological performance metrics and trophic energetics of ecosystems. I draw mostly from my knowledge of mammals, yet in many cases the mammalian examples can be generalized to other organisms. I end with prospects for further evaluating and extending the EFP.