Key Concepts

CONCEPT 21.1 Trophic levels describe the feeding positions of groups of organisms in ecosystems.

CONCEPT 21.2 The amount of energy transferred from one trophic level to the next depends on food quality and on consumer abundance and physiology.

CONCEPT 21.3 Changes in the abundances of organisms at one trophic level can influence energy flow at multiple trophic levels.

CONCEPT 21.4 Food webs are conceptual models of the trophic interactions of organisms in an ecosystem.