Larval behaviour of a giant damselfly: territoriality or size-dependent dominance?

Abstract. Behavioural interactions and habitat use by larvae of the giant damselfly, Megaloprepus coerulatus, were studied in Panama. These larvae live in water-filled holes in fallen and living trees. Despite potential advantages for larval territoriality in this species, M. coerulatus did not exhibit exclusive use of resources, probably because their prey were not spatially clumped. Both well-fed and starved larvae initiated agonistic displays typical of other damselfly species, and even small diVerences in relative size aVected their behaviour towards conspecifics. Habitat use in M. coerulatus varied with levels of food and cover. When cover was abundant, as it is in natural holes, larvae were hyper-dispersed. A larva rarely showed exclusive use of a given area from one day to the next, however, even when both cover and motile prey were experimentally limited. The ability of larger individuals to displace smaller ones as they move around the habitat is best described as size-dependent (and site-independent) dominance rather than territoriality. The results suggest that it is premature to characterize an animal as ‘territorial ’ on the basis of its behaviour in the laboratory, unless the abundance and distribution of resources that are provided are realistic, and the experimental design is suYcient to diVerentiate between size-dependent dominance and site-specific exclusion of conspecifics from a critical resource.? 1996 The Association for the Study of Animal Behaviou