A survey of the bottom fauna of streams in the Scottish Highlands part III seasonal changes in the fauna of three streams

摘要: 1. The paper deals with seasonal changes in the composition and amount, by number weight, of benthic organisms riffles three streams different character (Shelligan Burn, River Almond, Allt dos Mhuicarain). Of Shelligan Burn has richest, Mhuicarain poorest, chemical surrounding vegetation. The Almond similar surroundings to but contains a much greater concentration dissolved ions. 2. The technique used sample bottom fauna is critically examined compared that using Surber sampler. 3. The mean standing stocks fauna, as dry weight per m2, were 2.88 g for 0.93 0.70 Mhuicarain. greatest occurred May, April when high proportion large size prior emergence. After their emergence numbers animals fell 1/4 present 1/2. largest July February. 4. The collected from separated into 67 taxonomic categories, 37 which species. Fifty-three categories represented 45 49 Thirty-four 17 species, common all streams. The was quantitatively less than Burn. usually had dense populations species Almond. Some differences between faunas can be attributed special features Mhuicarain. 5. Details ofLeuctra inermis, Amphinemura sulcicollis, Isoperla grammatica, Ephemerella ignita andRhithrogena semicolorata caught streams, biomass size-frequency distribution are given. sampling programme extended over winters differing severity, no found sizes attained mid-February each year, considered grow during winter months. 6. Riffle stretches make up part examined, there pools slower flowing water and, they constitute about 10% surface area. Riffles sampled September. contained higher numerical density spring autumn. There significant difference densities two habitats.Leuctra spp. andBaetis several times more pools.Ecdyonurus April, concentrated heavier, burrowing such asDicranota spp., other Tipulidae andEiseniella densely distributed riffles.Chloroperla torrentium equal pools.