Task allocation in ant colonies within variable environments (a study of temporal polyethism: Experimental)

We briefly review the literature on the division of labour in ant colonies with monomorphic worker populations, and show that there are anomalies in current theories and in the interpretation of existing data sets. Most ant colonies are likely to be in unstable situations and therefore we doubt if an age-based division of labour can be sufficiently flexible. We present data for a type of small ant colony in a highly seasonal environment, concentrating on individually marked older workers. We show that contrary to expectation such workers undertake a wide variety of tasks and can even retain their ability to reproduce, even whilst younger workers are actively foraging. Our analysis shows that old workers occupy four distinct spatial stations within the nest and that these are related to the tasks they perform. We suggest that correlations between age and task in many ant colonies might simply be based on ants foraging for work, i.e. actively seeking tasks to perform and remaining faithful to these as long as they are profitably employed. For this reason, employed older workers effectively displace unemployed younger workers into other tasks. In a companion paper, Tofts 1993,Bull. math. Biol. develops an algorithm that shows how foraging for work can be an efficient and flexible mechanism for the division of labour in social insects. The algorithm creates a correlation between age and task purely as a by-product of itsmodus operandi.