Environmental Constraints in Temporary Fresh Waters and Their Consequences for the Insect Fauna

Temporary fresh waters are defined as bodies of fresh water that experience a recurrent dry phase of varying length that is sometimes predictable in both its time of onset and duration. The aquatic insects that live in these habitats are strongly influenced by 2 main groups of constraints, physicochemical and biological factors. Taxa particularly well-represented in temporary running waters are the Ephemeroptera, Hemiptera, Coleoptera, Trichoptera, and tipulid and chironomid Diptera. With the exception of Ephemeroptera, all these groups are common also in temporary lentic waters, but the latter also support many species of Odonata, together with culicid, ceratopogonid and ephydrid Diptera. In general, however, the diversity of aquatic insects is lower in temporary than in permanent waters. Seasonal succession of species is commonplace in temporary waters, affecting food web structure. Adaptations to drought are reviewed, and traits common to the most successful taxa include a highly flexible life cycle, temperature-linked development, possession of a diapausing or otherwise protected egg, and high powers of dispersal. A trend towards terrestrialisation of immature stages is noted amongst at least some members of even strongly aquatic taxa. Several directions for future research are discussed including study of the controlling influence of the biological environment on the fauna and the former's interaction with physicochemical influences, temporal variation in the structure of food webs, and genetic analyses of populations. A recommendation is made for greater quantification in data collection, particularly on seasonal changes in species abundance, their life histories, and trophic relationships, as this will allow greater opportunity for modelling the community dynamics of these ecologically distinct habitats. Finally, the concept that temporary waters constrain their faunas is exposed as being based more on human perception than on fact.