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Life of a River - Biology
River Continuum Concept: Midstream (pg 5 of 7)

As a result of this changing food base, relatively few shredders live in this stretch. Far more aquatic insects are collectors, eating phytoplankton as well as drifting bits of detritus. Many species are also grazers (also known as scrapers), gathering up attached periphyton. Among these grazers are various caddisflies, mayflies, riffle beetles, and aquatic snails.

The tiny but abundant midges collect food by all of these methods: shredding, collecting, scraping, eating other animals and even feeding directly on wood. The complexity of the physical environment-rocks, woody debris, rooted vegetation, soft sediment-as well as the varied food sources are important factors in the increase in numbers and diversity of the invertebrate community.

By now, the stream is getting warmer and is suitable to more species but may be too warm to support some, such as trout. This wider range of species finds shelter and food in the ever-increasing variety of habitats.

Most likely, the stream is deeper, with a regular pattern of riffles, runs, and pools. These provide critical habitat for minnows, darters, bass, sunfish, walleyes, bullheads and suckers. These fish, depending on the size and species, may feed at various times at all levels of the food chain, from phytoplankton, to aquatic insects, to other fish.

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Introduction
Flow
Shape
Connections
Quality
Life
Description
Terrestrial plants
Terrestrial animals
Life cycles
Corridors
Refuges
Aquatic habitats
Adaptations
Continuum concept
Relationships
Consequences
Stories
Summary
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