Meeting Abstract
In many complex systems, individual units show diversity in form and function. Often this is in the service of division of labor, such that specialized units perform particularly well in their tasks; in other cases, variation among individuals seems like random noise. Here we introduce another group-level benefit of diversity coupled with division of labor, based on the trade-off between unit costs and output. In social insect colonies, individual workers perform different tasks such as brood care, foraging, and others. Workers often differ in many traits, including body size. In bumble bees, worker body size variation is substantial (3-10fold within colonies). Overall, we show that smaller workers, while specializing on brood care over foraging, do not perform either task particularly well, and specifically are worse than larger workers. However, the optimal body size, taking into account production costs for workers, is different for brood care and foraging. Smaller workers perform less badly at brood care than they do at foraging, giving them a comparative advantage in this task, and generating a colony-level benefit of producing workers that differ in body size. We demonstrate theoretically that given a certain amount of resources to invest in producing workers, colonies do better by investing in a diversity of worker sizes, and that colony performance is driven more by the size of the largest workers than the average body size. We also show that how bumble bee colonies make these investment decisions under high or low food availability is consistent with this hypothesis. Our results indicate that benefits of worker diversity are varied and not restricted to producing highly efficient but narrow specialists.
