Intrageneric habitat segregations among chironomid species of several genera in river environments

With a view to clarifying intrageneric habitat segregations with respect to various environmental factors among species of four genera, Cricotopus, Polypedilum, Rheotanytarsus and Tanytarsus, compositions of adult males belonging to these genera were examined. The adult males emerged from materials attached to artificial substrates submerged at rapids or at pools of different sites in altitude, topographic type and electric conductivity in the Ohta River, Hiroshima Prefecture. Each environmental factor was categorized into three ranges and the range in which a species occurred in a significantly large number was regarded as the one the species requires. Thereafter, the differences in requirements between the congeneric species were examined. As a result, with respect to altitude, Polypedilum hiroshimaense was considered to require high altitude, whereas P. asakawaense and P. convictum; and P. japonicum and P. nubifer, were considered to require middle and low altitude, respectively. R. tamaquintus, R. tamasecundus and R. tamatertius all required high altitude. As regards topographic type, Tanytarsus tamakutibasi required Aa, whereas T. tamaoctavus; and T. oyamai, T. takahashii, T. tamagotoi and T. unagiseptimus required Aa-Bb and Bb/Bc, respectively. For the riverbed type, Cricotopus metatibialis and C. triannulatus; and C. bimaculatus required rapids and pools, respectively. Among the Tanytarsus species, only T. arduennensis required rapids. For electric conductivity, Rheotanytarsus tamaquintus and R. tamatertius required low conductivity. R. tamasecundus and R. fluminis required a middle and high level of conductivity, respectively.