Hierarchy and Its Relation To Territory in the Cockroach Nauphoeta Cinerea

Abstract

Abstract(I) The first aim of the study was to determine the role of the hierarchy in the social organisation of a group of male cockroaches and specifically to determine the advantages of high rank. The second aim was to see if social structure could be altered by changing the density. (2) On the basis of rank three classes of males can be distinguished. The characteristics of these three classes are described. (3) The main outcome of the hierarchy is that it determines a class of territorial males. Only top-dominant (alpha) males have absolute territorial rights. Bottom-ranking (gamma) males have none. The main evidence that territory holding itself does not confer dominance is that any change in the hierarchy is followed, rather than preceded by, a change in the animals holding territories. This type of organisation can be called territorial/hierarchical. (4) Gamma males are at a disadvantage only with respect to territory unless the group is very crowded (see below). They compete just as successfully as other males for food and water and also for females in non-territorial situation. (5) The hierarchy is stable for long periods and while it is stable the behaviour is predominantly territorial. Eventually changes in rank order do occur and possible explanations for this are discussed. (6) Groups of three densities were observed. Different social organisation is found with different degrees of crowding. At low density the society is territorial/hierarchical as described above. As the density increases so the number of territorial animals declines. At high density there is a marked change in the resting pattern. Most males clump together leaving wide unoccupied spaces. Only one male, the owner of the food territory, occupies the same site consistently. This male is not the top-dominant animal. Aggressive behaviour in middle-ranking males is inhibited and some bottom-ranking males show elements of the stress syndrome. There is a more rapid turn-over of top-ranking animals with increasing density. (7) When receptive females are introduced into a relatively stable group of males in a non-territorial situation, the level of aggression is raised and total disruption of the hierarchy follows. The implication of this observation is discussed. There was no correlation between rank and mating success.