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Consumers and Decomposers

Describes organisms that must consume other organisms, and organisms that break down dead organisms and animal wastes.

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Consumers and Decomposers_Mr.Sapora

License: CC BY-NC 3.0


Making a living in the icy waters of the Bering Sea.

Least Auklets spend almost every moment of their entire lives out in the North Pacific Ocean and Bering Sea.  How do these little birds find the energy to survive the harsh weather and riduclously cold waters you ask?  By diving down and consuming lots of high-calorie, fatty foods - mainly copepods and other forms of shrimp-like zooplankton.  Don't let their size fool you - these little birds are some serious consumers to be reconded with. 

Consumers and Decomposers

Recall that producers make their own food through photosynthesis. But many organisms are not producers and cannot make their own food. So how do these organisms obtain their energy? They must get their energy from other organisms. They must eat other organisms, or obtain their energy from these organisms some other way. The organisms that obtain their energy from other organisms are called consumers.  Consumers are organisms that depend on producers or other types of organisms for food. They are also called heterotrophs, which literally means “other nutrition.”  Heterotrophs are unable to make organic compounds (such as glocuse/sugar) from inorganic molecules and energy. Instead, they take in organic molecules by consuming other organisms. All animals and fungi and many bacteria are heterotrophs. A few insect-eating plants are also heterotrophic. Heterotrophs can be classified on the basis of the types of organisms they consume. They include herbivores, omnivores, and carnivores.

The consumers can be placed into different groups, depending on what they consume.


Herbivores are organisms that consume only producers such as plants or algae. In most ecosystems, herbivores form a necessary link between producers and other consumers. Herbivores transform the energy stored in producers to compounds that can be used by other organisms.

In terrestrial ecosystems, many animals and fungi and some bacteria are herbivores. Herbivorous animals include deer, rabbits, and mice. Herbivores may specialize in particular types of plants, such as grasses, or specific plant parts, such as leaves, nectar, or roots

License: CC BY-NC 3.0

Musk Ox - Cape Krusenstern, Alaska. These large herbivores live year-round in the arctic, where they feed on grasses, moss, and lichens. [Figure2]

In aquatic ecosystems, the main herbivores are the heterotrophic organisms that make up zooplankton. Zooplankton refers to all the small organisms that feed on phytoplankton. These organisms include both single-celled organisms such as protozoa and multicellular organisms such as jellyfish. Phytoplankton and zooplankton together make up large communities of producers and herbivores called plankton.


Carnivores are organisms that eat a diet consisting mainly of herbivores or other carnivores. Carnivores include lions, wolves, polar bears, hawks, frogs, fish, and spiders. Animals that eat only meat are called obligate carnivores. They generally have a relatively short digestive system that cannot break down the tough cellulose found in plants. Other carnivores, including dogs, can digest plant foods but do not commonly eat them. Certain carnivores, calledscavengers, mainly eat the carcasses of dead animals. Scavengers include vultures, raccoons, and blowflies.

A tiny minority of plants—including Venus flytraps and pitcher plants—are also carnivorous. These plants trap and digest insects. Some fungi are carnivorous as well. Carnivorous fungi capture and digest microscopic protozoan organisms such as amoebas.

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Arctic Fox - Arctic National Wildlife Refuge, Alaska. This little fox turns white in the winter and dark-brown in the summer. It will eat pretty much anything - birds and bird eggs during the summer mainly, and in the winter it will scavenge off of polar bear kills and anything else it can find. [Figure3]


Omnivores are organisms that eat both plants and animals as primary food sources. Humans are an example of an omnivorous species. Although some humans eat foods derived only from plants or only from animals, the majority of humans eat foods from both sources. Other examples of omnivorous animals are pigs, brown bears, gulls, and crows. Aquatic omnivores include some species of fish, such as piranhas.

License: CC BY-NC 3.0

Mr. Sapora cooking up some gravy in Alaska...sausage gravy goes great on green beans and that makes me a omnivore! [Figure4]


When a plant or animal dies, it leaves behind energy and matter in the form of the organic compounds that make up its remains. Decomposers are organisms that consume dead organisms and other organic waste. They recycle materials from the dead organisms and waste back into the ecosystem. These recycled materials are used by the producers to remake organic compounds. Therefore, decomposers, like producers, are an essential part of every ecosystem, and their stability is essential to the survival of each ecosystem. In essence, this process completes and restarts the "circle of life." As stated above, scavengers consume the carcasses of dead animals. The remains of dead plants are consumed by organisms called detritivores.

  • Herbivores are animals that eat producers to get energy. For example, rabbits and deer are herbivores that eat plants. The caterpillar pictured below (Figure below) is a herbivore. Animals that eat phytoplankton in aquatic environments are also herbivores.
  • Carnivores feed on animals, either herbivores or other carnivores. Snakes that eat mice are carnivores. Hawks that eat snakes are also carnivores (Figure below).
  • Omnivores eat both producers and consumers. Most people are omnivores, since they eat fruits, vegetables, and grains from plants, and also meat and dairy products from animals. Dogs, bears, and raccoons are also omnivores.

Examples of consumers are caterpillars (herbivores) and hawks (carnivore).

Decomposers and Stability

Decomposers (Figure below) get nutrients and energy by breaking down dead organisms and animal wastes. Through this process, decomposers release nutrients, such as carbon and nitrogen, back into the environment. These nutrients are recycled back into the ecosystem so that the producers can use them. They are passed to other organisms when they are eaten or consumed. Many of these nutrients are recycled back into the soil, so they can be taken up by the roots of plants.

The stability of an ecosystem depends on the actions of the decomposers. Examples of decomposers include mushrooms on a decaying log. Bacteria in the soil are also decomposers. Imagine what would happen if there were no decomposers. Wastes and the remains of dead organisms would pile up and the nutrients within the waste and dead organisms would not be released back into the ecosystem. Producers would not have enough nutrients. The carbon and nitrogen necessary to build organic compounds, and then cells, allowing an organism to grow, would be insufficient. Other nutrients necessary for an organism to function properly would also not be sufficient. Essentially, many organisms could not exist.

Examples of decomposers are bacteria (a) and fungi (b).


  • carnivore: Organism that feeds on other animals.
  • consumer: Organism that must consume other organisms to obtain food for energy.
  • decomposer: Organism that obtains nutrients and energy by breaking down dead organisms and animal wastes.
  • herbivore: Animal that eats producers to obtain energy.
  • omnivore: Animal that eats both producers and consumers.
  • producer: Organism that produces food for itself and other organisms.


  • Consumers must obtain their nutrients and energy by eating other organisms.
  • Decomposers break down animal remains and wastes to get energy.
  • Decomposers are essential for the stability and survival of an ecosystem.


Use the resource below to answer the questions that follow.

  1. What is the role of decomposers in an ecosystem? What is the source of the matter which is decomposed?
  2. How do the actions of earthworms improve soil quality? How does this impact the amount of biomass an ecosystem can support?
  3. How do gastropods function as decomposers?


  1. What’s the term for a consumer that eats both leaves and fish?
  2. What are the different types of consumers?
  3. Why are decomposers important in the ecosystem?

Image Attributions

  1. [1]^ License: CC BY-NC 3.0
  2. [2]^ License: CC BY-NC 3.0
  3. [3]^ License: CC BY-NC 3.0
  4. [4]^ License: CC BY-NC 3.0

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