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The Distribution of Benthic Invertebrates on Substrata in Fast-Flowing Streams

Henry J. Egglishaw
Journal of Animal Ecology
Vol. 38, No. 1 (Feb., 1969), pp. 19-33
DOI: 10.2307/2738
Stable URL: http://www.jstor.org/stable/2738
Page Count: 15
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The Distribution of Benthic Invertebrates on Substrata in Fast-Flowing Streams
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Abstract

1. The paper deals with the distribution of benthic invertebrates in stream riffles, with particular reference to the three main sources of plant food--plant detritus under stones in the bed of streams, clumps of moss growing on stones and the algal covering on the upper surface of stones. 2. The frequency distributions of the numbers of the commonest invertebrate species collected with plant detritus in samples from the stony beds of two streams of different character (Shelligan Burn and River Almond) were positively skewed. A logarithmic transformation made the distributions more normal. The ranked variances on the log scale of the commonest species present in both streams were significantly correlated. In the River Almond, where the samples were taken systematically, the populations of certain organisms (Isoperla grammatica, Rhithrogena semicolorata and Leuctra inermis) were fairly evenly distributed across the width of the stream, whilst others (Latelmis volkmari larvae, Esolus parallelopipedus larvae, Hydroptila spp. and Perla bipunctata) were clearly more dense in the centre of the stream. The numbers of twelve species in the Shelligan Burn and six in the River Almond increased with increase in the amount of detritus at sampling sites, and the numbers of two species in the Shelligan Burn and five in the River Almond increased with increase in the size of the largest stones at the sites. Of twenty-nine significant associations between different species and the environmental factors measured only one was negative. Since different species of bottom fauna had different quantitative relationships with plant detritus, the structure of the community at a site depended to a large extent on the amount of detritus present there. With increase in plant detritus there was also an increase in the variety of bottom fauna. 3. The populations of most species of bottom fauna were less aggregated in clumps of moss growing on stones than were populations in the under-stone habitat. There were differences in the species composition and in the length-frequency distributions of certain species of the fauna from both habitats. The numbers of no species living on the upper surface of stones and only the weight of bottom fauna in one of three streams examined was found to be significantly associated with the amount of algae present. 4. The bearing of the results on future work in stream ecology is discussed.

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