Food Chains and Food Webs

How does energy flow through ecosystems?

In every ecosystem, primary producers and consumers are linked through feeding relationships. Despite the great variety of feeding relationships in different ecosystems, energy always flows in similar ways. Energy flows through an ecosystem in a one-way stream, from primary producers to various consumers.

Food Chains You can think of energy as passing through an ecosystem along a food chain. A food chain is a series of steps in which organisms transfer energy by eating and being eaten. Food chains can vary in length. For example, in a prairie ecosystem, a primary producer, such as grass, is eaten by an herbivore, such as a grazing antelope. A carnivore, such as a coyote, in turn feeds upon the antelope. In this two-step chain, the carnivore is just two steps removed from the primary producer.

In some aquatic food chains, primary producers are a mixture of floating algae called phytoplankton and attached algae. As shown in Figure 3–7, these primary producers may be eaten by small fishes, such as flagfish. Larger fishes, like the largemouth bass, eat the small fishes. The bass are preyed upon by large wading birds, such as the anhinga, which may ultimately be eaten by an alligator. There are four steps in this food chain. The top carnivore is therefore four steps removed from the primary producer.

Figure 3–7 Food Chains Food chains show the one-way flow of energy in an ecosystem.

Apply Concepts What is the ultimate source of energy for this food chain?

d