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River as a Continuum
The river continuum concept, first proposed by Vannote and others in 1980, provides a model of changes that might take place as water travels from headwater streams to larger rivers. As stream size increases, the influence of the surrounding forest decreases. The river continuum concept provides predictions of the way that biological communities might change from headwater streams to larger rivers.

If small headwater streams depend on the surrounding forest for energy and nutrients, then leaf-shredding macroinvertebrates should constitute a large portion of the macroinvertebrate population. Grazers, those that scrape algae from rock surfaces, should be nearly absent from small streams, because these streams are well-shaded from sunlight by the surrounding forest. Collectors filter or gather fine particles from the stream and should be increasingly important in larger streams, where they take advantage of the fine fragments that are washed downstream from the headwaters. Predators should be common throughout the river system.

Compare the model below with the physical, chemical, and biological data from the Wheeling Creek watershed. Are macroinvertebrate roles in the Wheeling Creek ecosystem organized in a manner similar to that predicted by the river continuum concept?

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Shredders 1] [ Predators 1 ] [ Collectors 1] [ Grazers 1 ]
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