Food Chain

A food chain is the linear path along which energy moves from producers all the way up to the top carnivores — from producers to primary consumers, then to secondary consumers, and finally to tertiary consumers — forming a simple, linked, one-directional network. Two basic types occur in every ecosystem. The grazing food chain draws its energy ultimately from the sun and begins with living green-plant producers (its first link); the second link is a primary consumer such as a mouse feeding directly on the producer; the third link is a secondary consumer such as a snake preying on the primary consumer; and the fourth link is a tertiary consumer such as an eagle preying on the secondary consumer. The detritus food chain, by contrast, begins not with living producers but with dead organic matter (detritus) — a large and constant source of energy derived from dead plants, animals and their excreta, present in every ecosystem. Energy here passes through a chain of detritus consumers (detritivores, such as an earthworm) on to small carnivores (such as a blackbird) and finally to top carnivores (such as a hawk), with repeated eating-and-being-eate …