Spatial relationships within nests of the ant Leptothorax unifasciatus(Latr.) and their implications for the division of labour

Abstract

This paper investigates how the movement zones of all the ants in a colony are organized inside the nest. The workers in nine colonies of the ant Leptothorax unifasciatus(Latr.) were marked individually and their positions in the nest were recorded over 33 periods of observation spread throughout the year. Results from randomization tests demonstrated that the individual workers in L. unifasciatus colonies had movement zones of limited area. These are termed spatial fidelity zones (SFZs). SFZs were specific to individuals. They occurred with partial overlap, in a sequence from the colony centre to the colony periphery. The size of SFZs increased from the centre of the colony towards the periphery. The median size of SFZ in a colony varied with the time of year; they expanded gradually after hibernation with a peak in May and then contracted gradually until the following hibernation. The frequency of a worker's brood care behaviour was related to the amount of overlap between her SFZ and the spatial distribution of the brood. Individuals on the periphery of the colony were most likely to leave the nest. No clear segregation on the basis of age was observed. The division of labour in L. unifasciatus was flexibly organized along the continuum of SFZs where each worker performed the tasks within her spatial fidelity zone.