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Interdependence of food chains

Posted about 10 months ago by adumbperson


Producers, also called autotrophs, can make their own food. They form the first feeding or trophic level of all food chains and food webs and are the source of all of the food energy available in an ecosystem. In terrestrial (land) ecosystems, the primary producers are green plants. In aquatic ecosystems, various species of bacteria and protists called phytoplankton are the primary producers.

Most primary producers use the process of photosynthesis to trap energy from sunlight and convert carbon dioxide and water into food (glucose). A small number of producer organisms, such as bacteria living in underground hot springs or near deep ocean vents, do not have access to sunlight as an energy source for food production. Instead, they use the energy in gases like hydrogen sulfide to convert chemical compounds into food through a process called chemosynthesis. However, the vast majority of energy for all life on Earth ultimately comes from the Sun. Without light energy from the Sun, food production would not be possible and life on Earth could not exist.


All other organisms in ecosystems are either consumers or decomposers. Consumers, or heterotrophs, cannot manufacture their own food. They must consume the tissues of other organisms in order to get the energy they need to survive. Consumers that eat only plants are called herbivores. They form the second feeding, or trophic level, of all food chains and webs.

Organisms in this second trophic level are called primary consumers.

Sun - producers (green plants, phytoplankton)/ primary consumers (herbivores)

Consumers that eat only animal matter are carnivores. They form the third and fourth trophic levels of food chains and webs and are called secondary and tertiary consumers. Secondary consumers eat animals that eat plants while tertiary consumers eat animals that eat other animals. Tertiary consumers are sometimes called top carnivores because they are at the top, or apex, of a food chain or web and are not normally preyed upon by any other carnivore.

More producers and consumers

Which organisms in the field ecosystem below are primary and secondary consumers?

primary and secondary consumers

The cottontail rabbit eating the grass is a primary consumer while the red fox, which eats the rabbit, is a secondary consumer.

An organism that might consume the red fox, such as a cougar, would be a tertiary consumer. (Keep in mind that carnivores such as cougars would also prey upon primary consumers as well.)

Some consumer organisms, like humans, raccoons, cockroaches, and black bears, that eat both plants and animals are called omnivores. Omnivores play more than one role in food chains and webs and can be primary, secondary, or tertiary consumers.

Some carnivores do not kill animals themselves, but instead feed on the bodies of animals that are already dead. By doing so, they perform an important sanitation service. These specialized carnivores, such as catfish and vultures, are called scavengers.


One of the most important laws of nature is the Law of Conservation of Matter. It states that, with the exception of a minute amount of cosmic dust falling to Earth from space, new matter cannot be created. In other words, the total amount of matter on Earth is finite and does not change. This means that all of Earth's carbon atoms and other chemical building blocks of life must be constantly recycled in order for new organisms to form and grow. The carbon atoms making up your body are the same carbon atoms that were around during the age of the dinosaurs and before!

If ecosystems only contained producers and consumers, the matter stored in their bodies would never be returned to the cycle of life. When organisms in an ecosystem die, their bodies need to be broken down to release the carbon and other chemicals stored in their tissues. This is where decomposers step in. They are nature's recyclers, breaking down the complex organic molecules of dead organisms and their wastes into simpler inorganic compounds that are then used to form new organisms.

The majority of decomposers are bacteria and fungi such as mushrooms.