Ant stoichiometry: elemental homeostasis in stage-structured colonies

1. Organisms facing variation in food quality maintain elemental composition within limited bounds. Such stoichiometric homeostasis has often been considered a speciesspecific parameter, but stoichiometry can also vary intraspecifically across life stages, sexes and sizes. In colonial organisms with overlapping generations, stoichiometric variation among stages could lead to flexibility in colony-level elemental composition due to changes in internal demography. 2. We examine how the balance of energy (sucrose) and nutrients (prey) affects growth rate and carbon : nitrogen : phosphorus (C : N : P) homeostasis in a eusocial insect, the pavement ant Tetramorium caespitum . 3. Colony growth depended heavily on prey availability. However, sucrose scarcity led to higher worker mortality and production of smaller workers, suggesting sucrose availability will affect colony-level performance in a competitive environment. 4. In contrast, C : N : P stoichiometry of larvae, pupae, and workers varied mostly with sucrose availability. Biomass P content within life stages was lower in colonies receiving less access to sucrose. We suggest this difference arose primarily from shifts in individual ant mass coupled with negative P-body mass relationships. 5. Life stages differed considerably in elemental composition, and resource conditions affected colony stage structure. Nevertheless, variation in colony-level stoichiometry primarily reflected compositional differences within stages rather than shifts in internal demography.