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Habitat Preferences in Net-Spinning Caddis Larvae with Special Reference to the Influence of Water Velocity

J. M. Edington
Journal of Animal Ecology
Vol. 37, No. 3 (Oct., 1968), pp. 675-692
DOI: 10.2307/3081
Stable URL: http://www.jstor.org/stable/3081
Page Count: 18
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Habitat Preferences in Net-Spinning Caddis Larvae with Special Reference to the Influence of Water Velocity
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Abstract

1. Recent taxonomic work on net-spinning caddis larvae has made it possible to investigate them from an ecological point of view. 2. The taxonomic background is outlined for each family and descriptions are given of the various types of feeding nets constructed by the larvae. 3. The present work is concerned with the habitat preferences shown by the larvae, and especially the possibility that some species are `slow flow' specialists and others `fast flow' specialists. 4. A sampling programme was carried out on two stream systems at Rothbury in Northumberland. This revealed that the dominant species in rapids were different from those in pools. It also showed that there was a sequential replacement of species down the length of each stream system. 5. The association of species with either rapids or pools was found to be based on water velocity preferences. Using a miniature flow meter it was possible to measure the velocity ranges occupied by different species. For Hydropsyche instabilis, a rapids species, the range is 15-100+ cm/sec, for Plectrocnemia conspersa, a pools species 0-20 cm/sec. 6. An attempt is made to correlate this difference in distribution with structural and behavioural attributes of the two species. 7. In both species the structure of the net appears to limit the range of water velocity at which it can be used. 8. In two field experiments the flow patterns in a stream were altered. The behaviour of Hydropsyche instabilis larvae allowed them to maintain contact with areas of high velocity. 9. Using a flowing water tank, observations were made on the ability of the two species to spin nets at various water velocities. For each species net-spinning activity was greatly reduced in velocities outside those occupied in the field. 10. The evidence is discussed for respiratory differences between slow flow and fast flow species. 11. It is argued that the foregoing demonstration of specialization to particular water velocities provides an explanation for the distribution of the larvae between rapids and pools. 12. A similar approach is advocated in the study of other discontinuities of distribution shown by stream animals.

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