川の底棲動物の現存量をめぐる諸問題 特に造網型昆虫の重要性について

Abstract

Some problems on the standing crop of Japanese streams are discussed.(1) Except the extreme examples, which may have the weight of 20 gr to 30 gr, the quadrate (50 cm × 50 cm) samples of more than 5 gr in weight show very rich fauna.(2) In general the standing crop of “Hayase” -rapids is more than that of “Hirase” -rapids, and the standing crop of rapids is more than that of pools.(3) Among the life forms, such as crawling form, net-spinning form, casebearing form, swimming form, etc. (TSUDA et al., 1953), the net-spinning form is, with a few exceptions, the dominant life form, when the samples are of more than 5 gr.(4) When the weight of quadrate samples is more than 5 gr, the rate of netspinners to the total benthic animals (net-spinner's percentage, or net-spinner's coefficient) is, with only a few exceptions, more than 80 %. And, when the weight of quadrate samples is less than 5 gr, the net-spinner's percentage is diverse.(5) When the weight of quadrate samples is more then 5 gr, the rate of the second consumers to the total benthic animals (second consumer's percentage, or second consumer's coefficient) is usually less than 20%. And, when the weight of samples is less than 5 gr, the second consumer's percentage is diverse, though less than 40% in most cases.(6) As for the insect production of Japanese streams, the net-spinners, especially the Stenopsychid-larvae, appear to play a very important role.