Trophic Relationships

Abstract

The trophic categories of riverine food webs reflect the basal resources available to consumers, including benthic and planktonic algae, detritus with its associated microbial assemblage, higher plants, and other animals. Invertebrates typically are divided into functional feeding groups and fishes into guilds. Among the invertebrates, grazers ingest periphyton, shredders feed on large particles of organic matter such as leaves, collectors feed on small organic particles either from suspension or the streambed, and predators feed on other animals. Fish trophic categories rely primarily on what resources is consumed, but also may consider feeding location and morphology. Commonly used categories include herbivores, detritivores, planktivores, omnivores, benthic invertivores, midwater-surface feeders, and piscivores. Amphibians, reptiles, birds, and mammals also can be important in riverine food webs. Many consumers are generalist feeders, however, and so trophic organization in river ecosystems can be complex and indistinct. Studies often refer to the high frequency of dietary plasticity, or characterize many of the species present as omnivorous, generalists, or opportunists. Even in the tropics, where some wonderful examples of ecological specialization can be found, many observers have opined that a generalist or opportunistic feeding strategy seems to characterize most species.