In 1942, American ecologist Raymond Lindeman (1915–1942) was one of the first ecologists to refer to the “trophic dynamics” of ecosystems. Today, scientists use the term trophic level to represent a step in the dynamics of energy flow through an ecosystem. The first trophic level is made up of the producers, or those within an ecosystem that harvest energy from an outside source (like the Sun or deep-sea thermal vents), and stabilize or “fix” it so that it remains in the system. The second level would be those who consume the producers, also known as the primary consumers; the next level would be the secondary consumers (those who consume the primary consumers), and so on. Because of the limited amount of energy available to each level, these trophic pyramids rarely rise above a third or fourth level of structure.
Large predators like this wolf were once thought to be keystone species that were essential to the health of an ecosystem because of their role in controlling populations. Now scientists know many less conspicuous species are vital, too.