Patterns and processes in freshwater systems: the social dimension

Abstract

Social interactions within species present an under-appreciated complicating factor in freshwater ecology. Such processes can markedly alter distribution patterns. Odonata are an important group of animals in freshwater systems and have the capacity, under some circumstances, to exclude other organisms (invertebrate and vertebrate) from otherwise suitable habitats. Within the Odonata stylised agonistic behaviours are widespread in larvae of Zygoptera and have important consequences for both the ecology of the species concerned and for the impact of zygopteran larvae within ecosystems. In this paper the diversity of agonistic displays within the Zygoptera is reviewed. On phylogenetic grounds, supported by fossil dates, zygopteran display systems are very ancient (~ 150-200 My). Given the obvious costs in energy, increased exposure to predators, and the real risk of damage during interactions, agonistic behaviours must have considerable adaptive significance. Investigations of the processes involved in social interactions, and how they generate the patterns that are more generally recorded, will probably require a return to large aquarium studies, or to in situ examination of microhabitats using underwater observatories.