Ecological stoichiometry: Overview

Ecological stoichiometry is the study of the balance of energy and multiple chemical elements in ecological interactions. Organisms exhibit considerable variation in their chemical composition but this variation occurs within important biological limits set by the chemical composition of the major biological molecules used by living things. Organisms differ in the degree to which they homeostatically regulate their chemical composition. Photoautotrophic organisms (cyanobacteria, algae, vascular plants) appear to be plastic in adjusting their elemental composition according to growth conditions while animals more tightly regulate their chemical composition around species- or stage-specific values. This contrast in stoichiometric homeostasis imposes important stoichiometric constraints on food webs due to food-quality constraints and results in large-scale feedbacks via differential nutrient recycling by consumers. Recent work has identified determinants of variation in stoichiometric constraints in ecosystems due to variations in light:nutrient ratios and in the C:N:P ratios of diverse biota due to differences in patterns of allocation to P-rich RNA associated with variation in growth rate. Thus, ecological stoichiometry connects evolutionary patterns affecting organismal elemental composition to large-scale consequences and constraints associated with energy and material flows in ecosystems.