Organism-substrate relationships in lowland streams

A field and laboratory study on the microdistribution of bottom dwelling macroinvertebrates to investigate the role of the stream substrate In the development and preservation of the macroinvertebrate communities in natural, undisturbed lowland streams is described. Field data on bottom substrates and fauna wore collected between 1975 and 1978 from two Dutch lowland streams. Substrates were characterized by the nature and the amount of organic detritus and the mineral particle sizes: in a field classification on the basis of the visually dominant particle sizes; in a grain-size classification on the basis of exact particle-size analysis in the laboratory. Substrate preference for 84 macroinvertebrate species was demonstrated using the Index of Representation.Substrate-selection experiments were conducted in a laboratory stream for three Trichoptera species (Micropterna sequax, Chaetopteryx Villosa and Sericostoma personatum) and one Ephemeroptera species (Ephemera danica). An experiment on the colonization of artificial substrates in the field was also conducted.Prom the field data, several faunal groups could be distinguished, each group made up of species with similar substrate preferences. Detailed data on the microdistribution in relation to substrate particle size are given for 26 species, which represent the various taxonomical units that compose the faunal groups: Trichoptera (5 species), Ephemeroptera (1 species), Plecoptera (1 species), Coleoptera (3 species), Amphipoda (1 species), Diptera (15 species, among which 13 species of Chironomidae). The microdistribution is discussed in relation to case-building behaviour, life cycle and food preferences. For several species substrate preferences may be different for different development stages or in different seasons.It is concluded that most species show distinct preferences for a specific substrate. The small scale spatial variation in substrate composition of the stream bed is essential for the existence of many lowland stream macroinvertebrate species.