Functional feeding groups are a classification approach that is based on behavioral mechanisms of food
acquisition rather than taxonomic group. The same general behavioral mechanisms in different species can
result in the ingestion of a wide range of food items. The benefit of this method is that instead of
hundreds of different taxa to be studied, a small number of groups of organisms can be studied collectively
based on the way they function and process energy in the stream ecosystem. Individuals are categorized based
on their mechanisms for obtaining food and the particle size of the food, and not specifically on what they
are eating.
This method of analysis avoids the relatively non-informative necessity to classify the majority of aquatic
insect taxa as omnivores and it establishes linkages to basic aquatic food resource categories, coarse
particulate organic matter (CPOM), and fine particulate organic matter (FPOM), which require different
adaptations for their exploitation. The major functional feeding groups are: scrapers (grazers), which
consume algae and associated material; shredders, which consume leaf litter or other CPOM, including wood;
collectors (gatherers), which collect FPOM from the stream bottom; filterers, which collect FPOM from the
water column using a variety of filters; and predators, which feed on other consumers. A sixth category
includes species that do not fit neatly into the other categories such as parasites. It is important to keep
in mind, however, that many kinds of invertebrates use a variety of food acquisition methods.