Animals in a Food Web

Students should understand that animals eat other animals, plants or both to obtain energy. Animals that eat only plants are called herbivores, and those that eat other animals are called carnivores.

All of these organisms are connected and depend on one another in a food chain. Animals at the top of a food chain are called apex predators.


A food web shows the feeding relationships among species in a biological ecosystem. Living organisms that make their own food by a process known as photosynthesis are called autotrophs. These include plants such as grass, moss and lichen, and algae. Other organisms that can’t make their own food and get it by eating other living organisms are called heterotrophs. Heterotrophs include animals, including humans, and other invertebrates, such as earthworms and mushrooms.

In a food chain diagram, arrows point from an organism to the animal that eats it. The organisms at the bottom of the pyramid are the producers, and the consumers that eat them are shown as dots connected by lines. The color of the dots indicates whether they are herbivores, carnivores or omnivores.

Sometimes, a keystone species in an ecosystem supports the entire food web. For example, a lynx keeps the population of mice in check, which in turn maintains healthy numbers of green plants. If a lynx were to disappear, however, the whole system would change.

Primary Consumers

Plants are referred to as autotrophs and they take in energy from the Sun through photosynthesis. This gives them organic molecules which they release into the environment as sugars and oxygen. Animals that consume these plants are heterotrophs, or consumers. They may be herbivores, carnivores or omnivores. They obtain the organic molecules they need by eating other living creatures, or by scavenging from dead organisms.

Primary consumers are the first link in a food chain. They eat the photosynthetic algae and other producers in their biome. In the desert, this might include butterflies that feed on cactus flowers and other primary producers. Primary consumers in the ocean are mollusks that eat phytoplankton and other primary producers. These organisms are then eaten by a yellow perch, a secondary consumer. The yellow perch eats other fish, and the top predator in the ecosystem, the sea lamprey, is a tertiary consumer.

In a healthy food web there are many herbivores and some carnivores or omnivores. This helps to ensure that the ecosystem has a balanced supply of nutrients and oxygen.

Secondary Consumers

Secondary consumers are found in many of the Earth’s ecosystems, from arid savannahs to the icy waters of the Arctic. They are omnivorous or carnivorous, but the one thing they all have in common is that they consume animals at the first and second trophic levels.

In a terrestrial ecosystem, squirrels who eat nuts and fruits are secondary consumers, as do foxes, cats, dogs, owls, and birds that hunt and prey on other creatures. Secondary consumers in aquatic ecosystems include sea otters that hunt sea urchins.

Scientists group animals into trophic levels to help them understand the relationships between them. Animals at higher trophic levels, like lions that eat grass and zebras that eat grazing antelope, depend on the lower links in the food chain to survive. For example, if there were no antelope, the zebras would have nothing to eat and they too would die out. The same is true if the lions did not eat grass, and so on. This is why it’s important to maintain healthy populations of the lower level species.

Tertiary Consumers

Animals that prey on both primary and secondary consumers are called tertiary consumers. They are the fourth level of a food chain, or trophic pyramid. They can also be called apex predators. These organisms consume other animals for their energy and are a vital part of every ecosystem. As they feed, they also contribute to the decomposition process by breaking down their bodies.

Terrestrial tertiary consumers include foxes and snake hunters like the venomous secretary bird. They are opportunistic and will eat anything that will sustain them, including plants like berries. They can be found in rainforests, deserts, and even snow and ice. They may be eaten after they die by scavengers and decomposers, but while alive tertiary consumers are not preyed upon by any other animals. These apex predators are important for keeping populations of the lower levels under control and preventing a trophic cascade from getting out of hand. This is why we should never hunt or poach these magnificent beasts. They are not only beautiful but they are essential to our planet.


A food web is a network of organisms that share the same food sources. Organisms are grouped into different categories depending on their place in the food chain. The categories are called trophic levels. Each level explains what kind of organism eats what and how much.

Each trophic level contains organisms that can make their own food. The organisms that can make their own food are called producers. They are the base of the food chain. They make the oxygen, carbon dioxide, and other nutrients that all living things need.

The next trophic level includes consumers that eat plants or other animals. Some consumers can eat organisms at more than one level, such as a sparrow that eats both worms and caterpillars.

Food chains often do not show decomposers. But without them, dead plants and animals would keep piling up with the nutrients the soil needs trapped inside. Then the ecosystem would be out of balance.