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Grazing Insects Mediate Algal Interactions in a Stream Benthic Community

David D. Hart
Oikos
Vol. 44, No. 1, Plant-Animal Interactions. Proceedings of the Third European Ecological Symposium. Lund, 22-26, August 1983 (Mar., 1985), pp. 40-46
Published by: Wiley on behalf of Nordic Society Oikos
DOI: 10.2307/3544041
Stable URL: http://www.jstor.org/stable/3544041
Page Count: 7
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Grazing Insects Mediate Algal Interactions in a Stream Benthic Community
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Abstract

Descriptive and experimental field studies were conducted to assess the ability of the grazing caddisfly larva Leucotrichia pictipes (Trichoptera: Hydroptilidae) to mediate interactions between algal populations living in a stream benthic community. Patches of low-growing algae (especially diatoms and Schizothrix calcicola) are sometimes interspersed among much thicker mats of the filamentous blue-green alga Microcoleus vaginatus in Augusta Creek, Michigan (USA). Within Leucotrichia's foraging area, Microcoleus is rare, whereas the alga's abundance increases dramatically outside the limits of the insect's foraging area. Experimental removal of Leucotrichia larvae from their diatom-Schizothrix covered foraging areas resulted in the rapid overgrowth of these areas by Microcoleus. Because Microcoleus filaments were not found in the guts of Leucotrichia larvae living in Microcoleus-fringed foraging areas, I suggest that these insects remove but do not ingest the blue-green alga, to prevent it from encroaching on preferred algal types. Regardless of the precise mechanism(s) by which Leucotrichia maintain their diatom-Schizothrix "lawns", the data demonstrate that the presence of this grazing insect has a pronounced effect on the local abundance and species composition of the algal community.

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