Trophic relationships

Abstract

Trophic organization in river ecosystems can be both complex and indistinct. Many consumers are polyphagous rather than monophagous, and exhibit considerable overlap with one another in their diets. The gut contents of invertebrates usually are difficult to distinguish, so these consumers are often characterized by the unspecific term of herbivore-detritivore. At least in temperate waters, the vast majority of fishes eat invertebrates. As a consequence, while a particular species may be classified solely on the basis of what it eats (herbivore, carnivore, detritivore and so on) the resulting categories are of limited usefulness because they offer too few distinctions among feeding roles. Some improvement may occur as advances are made in the characterization of food sources. However, it has proved more useful to distinguish among feeding roles on the basis of how the food is obtained, rather than solely in terms of what food is eaten. When several species consume a common resource and acquire it in a similar fashion, they are considered members of the same guild. Thus, a fish species that captures invertebrate prey directly from the bottom would occupy a different guild from another species that consumes the same prey, but captures it from the water column.