From Organism Traits to Ecosystem Processes: Why Size is So Important

Understanding the relationships between organism traits and ecosystem processes is crucial for advancing ecological theory and predicting ecosystem responses to environmental change. Fundamental biological functions—metabolism, growth, reproduction—scale predictably with organism size across diverse taxa. Moreover, scaling relationships are pervasive across organizational levels, governing population density, competitive interactions, and trophic food webs. This review synthesizes theoretical and empirical evidence linking organism size to ecosystem processes, highlighting the significance of allometric scaling laws, including the metabolic scaling theory and the energy equivalence rule. It discusses deviations from these predictions due to environmental heterogeneity, biotic interactions, and evolutionary dynamics. By exploring the role of size in modulating functional traits and ecosystem-level outcomes, we emphasize the need for integrated approaches to refine predictive models. This review underscores the centrality of size as a key driver of ecological processes and its implications for biodiversity conservation.