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 species-specific 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.