Scaling of work and energy use in social insect colonies

Abstract

Group size has profound effects on the organization of work. In the social insects, larger colony size is consistently associated with lower mass-specific energy use; similar hypometric relationships between group size and per-gram energy use may extend across other social taxa. The specific mechanisms driving social metabolic scaling vary among species, but evidence suggests that it can be associated with organizational changes in work (task) performance that allow more efficient energy use by larger groups. In social insect colonies, larger group size allows stronger individual specialization, greater diversity in task performance, and likely gives improved resilience to stochastic events. Larger colonies often also allocate a larger proportion of workers to maintenance and reserve rather than to foraging and brood care tasks, potentially reducing costs. For the few species examined, these organizational changes seem to be associated with lower mean but higher variance in movement rates, providing a concrete connection to metabolic use. Interestingly, colony group size is not generally associated with changes in the proportional number of colony workers resting versus doing work, but this may vary across social systems. Colonies with hypometric metabolic scaling tend to show constant or greater efficiency of brood production, consistent with efficiency rather than constraint-based scaling models. These patterns of work and energetics in social groups show distinct parallels with organismal scaling. Investigation into social metabolic scaling could contribute to identifying unifying scaling theories for the disparate fields of animal behavior, physiology, and human sociology.