Biomass competition unifies individual and community scaling patterns

Both metabolism and growth scale sublinearly with body mass for most species. Ecosystems show the same sublinear scaling between production and total biomass but ecological theory cannot reconcile the existence of these nearly identical scalings at different levels of biological organization. We solve this paradox using marine phytoplankton to connect individual and ecosystem scalings across three orders of magnitude in body size and biomass. Competitive interactions determined by biomass, rather than differences in species size, slow metabolism in a consistent fashion across species that dominates over species-specific peculiarities, resulting in a unique behavior across community compositions. The allometry of ecosystem production thus emerges from this metabolic density-dependence, independently of the equilibrium state or resource regime of the system. Our findings demonstrate the mechanistic basis of ecosystem allometries, unifying aspects of physiology and ecology to explain why growth patterns are so strikingly similar across scales.