Tertiary consumers are animals that eat other animals. In order to be a tertiary consumer, an animal must be a carnivore or an omnivore.
In the food chain, tertiary consumers are at the top. Producers are at the beginning of the food chain. Organisms like autotrophs are producers. Primary consumers are the next link in the chain. The secondary consumer eats the primary consumers, and the tertiary consumer eats the secondary consumer. Last on the food chain are the decomposers; these animals feed off the dead and break down the nutrients depositing to the soil.