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Macroinvertebrates can be grouped according to their primary food resource.

Macroinvertebrates are often grouped into functional feeding groups. A functional feeding group refers to the type of food resource that a particular species utilizes in the stream. The four major functional groups are:

  • Collectors (filtering and gathering) – This group includes organisms that filter small particulate organic matter from the water column. Small particulate matter is present in nearly all streams, including those in poor condition. This type of organic material is usually the result of degradation of algae, etc. from within the stream or the “leftovers” of larger pieces of organic matter that have been added to the stream. This material, which is generated within the stream itself, is an example of autochthonous material (auto- = self)
    • Examples: black fly larvae, riffle beetles, bivalves (clams), planaria
  • Scrapers – This group includes organisms that scrape algae from the surface of rocks and stream plants. Like collectors, scrapers utilize organic matter that is derived from the stream itself. Scrapers would dominate in a steam that lacks shading from the surrounding riparian zone, as long as there is sufficient substrate (rocks, etc) for algae to grow on.
    • Examples: mayfly nymph, snails
  •  Shredders – Shredders are organisms that feed on larger pieces of organic matter, such as leaves. The presence of these organisms indicates that there is sufficient input of larger pieces of organic matter into the stream from the surrounding riparian zone. This input of material from outside the stream is referred to as allochthonous material (allo- = other).
    •  Examples: sowbug and scuds (crustaceans), cranefly larvae
  • Predators – Predators are species that feed on other stream invertebrate species. The presence of predators in the stream indicates that there are sufficient resources available to support a stable, multilevel food web.
    • Examples: dobsonfly larvae, damselfly nymph, dragonfly nymph

Watch some amazing underwater footage of these different types of stream invertebrates in action:

Concept Check Question:

Which of the following statements about functional feeding groups is FALSE?:

A. Invertebrates are grouped according to food source.

B. Shredders require allochthonous input from the riparian zone.

C. Collectors would be the dominant group in a stream that is in excellent physical condition.

D. Scrapers feed on algae found on rocks and plants in the stream.


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