THE RUNNING-WATER BEETLES (COLEOPTERA) OF A RIVER CATCHMENT IN NORTHERN ENGLAND

202 running-water sites in the catchment of the River Rede, a tributar y of the River Tyne in northern England, were sampled for invertebrate s in 1990. The distributions of water beetle species were investigated using logistic regression with several environmental factors. A numbe r of site structure characteristics were assessed and the presence or absence of silt (as peat or clay) was found to be the most important s ingle variable. Shingle, pebbles, cobbles, boulders and the amount of vegetation present were less important substrate variables. The distan ce from stream source reflected substrate structure and site gradient was a poor determinant of species distribution. A composite variable, termed the exposure index, was derived from all the site structure cha racteristics using an ordination and was found to be useful in explain ing species distribution. Water pH also affected distributions conside rably. Two variable analyses using the exposure index and water pH gav e the best explanation of species distribution. The two variables used together were a reflection of productivity and disturbance, the two m ain components of habitat templates and strategy theory. The distribut ion of water beetle species in the Rede catchment was a product of the se factors, which, in turn, were a product of the geography of the cat chment.