Effect of a Caddisfly on Black Fly Density: Interspecific Interactions Limit Black Flies in an Arctic River

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TitleEffect of a Caddisfly on Black Fly Density: Interspecific Interactions Limit Black Flies in an Arctic River
Publication TypeJournal Article
Year of Publication1988
AuthorsHershey, AE, Hiltner, AL
JournalJournal of the North American Benthological Society
Accession NumberARC31

In a whole-river fertilization experiment, density of the dominant caddisfly, Brachycentrus americanus, was significantly higher downstream of fertilizer addition, while black fly density was significantly lower. In a caging experiment where Brachycentrus density was manipulated, black flies were significantly less abundant in high-density Brachycentrus cages than in ambient- and low-density Brachycentrus cages. Microcosm experiments and gut analyses showed that Brachycentrus--black fly encounters did not result in predation, but sometimes resulted in black fly drift. Black flies were more abundant on river rocks without conspicuous periphyton cover, but in microcosms they preferred periphyton-covered rocks. In microcosms the presence of periphyton resulted in a shift in black fly distribution from the tops of rocks to the bottoms and sides of rocks, the preferred microhabitat of Brachycentrus. Brachycentrus in microcosms did not affect black fly microhabitat preference. Increased periphyton abundance in the fertilized river probably did not reduce black fly abundance directly, but may have caused black flies to occupy a different microhabitat on the rocks, where they were more likely to encounter caddisflies. Results from the stream caging experiment and the microcosm experiments combined suggest that caddisfly dislodgement of black flies accounted for the observed lower density of black flies in the fertilized river.

Short TitleEffects of caddisfly activity on black fly density: Interspecific interactions outweigh food limitation