Mean mass-specific metabolic rates are strikingly similar across life's major domains: Evidence for life's metabolic optimum

TLDR

The fundamental question of how much energy life expends per unit mass per unit time remains unanswered. The study aims to determine whether metabolic rates are homeostatic across diverse life forms. The authors analyze a database of 3,006 species spanning bacteria to elephants, algae to sapling trees. Across 3,006 species, mean resting metabolic rates converge to a narrow 0.3–9 W kg⁻¹ range, a 30‑fold variation far smaller than the 4,000–65,000‑fold spread expected from universal scaling, indicating that natural selection favors organisms within this optimal physiological window.

Abstract

A fundamental but unanswered biological question asks how much energy, on average, Earth's different life forms spend per unit mass per unit time to remain alive. Here, using the largest database to date, for 3,006 species that includes most of the range of biological diversity on the planet—from bacteria to elephants, and algae to sapling trees—we show that metabolism displays a striking degree of homeostasis across all of life. We demonstrate that, despite the enormous biochemical, physiological, and ecological differences between the surveyed species that vary over 10 20 -fold in body mass, mean metabolic rates of major taxonomic groups displayed at physiological rest converge on a narrow range from 0.3 to 9 W kg −1 . This 30-fold variation among life's disparate forms represents a remarkably small range compared with the 4,000- to 65,000-fold difference between the mean metabolic rates of the smallest and largest organisms that would be observed if life as a whole conformed to universal quarter-power or third-power allometric scaling laws. The observed broad convergence on a narrow range of basal metabolic rates suggests that organismal designs that fit in this physiological window have been favored by natural selection across all of life's major kingdoms, and that this range might therefore be considered as optimal for living matter as a whole.