On a sawgrass prairie in the Florida Everglades, an alligator (Alligator mississippiensis) lazes on the bank of a slow-moving water channel. A great egret (Ardea alba) stalks fish in the shallows. A grasshopper (Brachystola magna) chews on an aster leaf. A raccoon (Procyon lotor) digs in the mud for freshwater mussels. These animals are quite different from one another and live in different ways, but they have something in common: In this ecosystem, they are all consumers.

Within every ecosystem, organisms interact to move energy around in predictable ways. These interactions can be represented by what scientists call a trophic pyramid. Primary producers—plants, algae, and bacteria—make up the base of the pyramid, the first trophic level. Through a process called photosynthesis, producers capture energy from the sun and use it to create simple organic molecules, which they use for food.

Consumers constitute the upper trophic levels. Unlike producers, they cannot make their own food. To get energy, they eat plants or other animals, while some eat both.

Scientists distinguish between several kinds of consumers. Primary consumers make up the second trophic level. They are also called herbivores. They eat primary producers—plants or algae—and nothing else. For example, a grasshopper living in the Everglades is a primary consumer. Some other examples of primary consumers are white-tailed deer that forage on prairie grasses, and zooplankton that eat microscopic algae in the water.

Next are the secondary consumers, which eat primary consumers. Secondary consumers are mostly carnivores, from the Latin words meaning “meat eater.” In the Everglades, egrets and alligators are carnivores. They eat only other animals. Most carnivores, called predators, hunt and kill other animals, but not all carnivores are predators. Some, known as scavengers, feed on animals that are already dead.

Some consumers feed on live animals but do not kill them. For example, small arachnids called ticks attach themselves to other animals and feed on their blood, but ticks are not considered predators. They are instead called parasites.

Some secondary consumers eat both plants and animals. They are called omnivores, from the Latin words that mean “eats everything.” A raccoon is an example of an omnivore; it eats plant matter such as berries and acorns, but it also catches crayfish, frogs, fish, and other small animals.

Ecosystems can also have tertiary consumers, carnivores that eat other carnivores. A bald eagle is an example of a tertiary consumer you might see near the coastal mangrove islands of the Everglades. Its diet includes predatory fish that eat algae-eating fish, as well as snakes that feed on grass-eating marsh rabbits. It is considered a “top predator” because no other animals native to the ecosystem hunt or eat it. When a top predator dies, it is consumed by scavengers or decomposers.

In addition to consumers and the producers that support them, ecosystems have decomposers. These organisms get their nourishment from dead organic material, such as decaying plant leaves or dead fish that sink to the bottom of a pond.