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Bacteria and fungi

Filter feeders (midge larvae, clams)

Predators

Figure 15.17 Allochthonous food web with functional groups. (Modified from Horne and Goldman, 1994.)

tions. As streams merge and move farther from their sources, FPOM increases relative to CPOM and the shredders give way to collectors and filterers. Farther downstream the river may acquire an autochthanous character based on attached algae and macrophytes, with grazers and collectors dominating. Finally, the river may become more like a lacustrine environment, dominated by collectors living off phytoplankton. The ratio of production to respiration exceeds 1, whereas respiration dominates at other parts of the river. Diversity is also greatest in this section. Figure 15.18 illustrates these changes with increase in river

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