Energy Flow in Ecosystems

Rabbit eating a flower

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If there is only one thing you learn about ecosystems, it should be that all of the living residents of an ecosystem are dependent upon one another for their survival. But what does that dependence look like? 

Each organism living in an ecosystem plays an important role in the flow of energy within the food web. The role of a bird is very different from that of a flower. But both are equally necessary to the overall survival of the ecosystem, and all of the other living creatures within it.

Ecologists have defined three ways that living creatures use energy and interact with one another. Organisms are defined as producers, consumers, or decomposers. Here is a look at each of these roles and their place within an ecosystem.


The main role of producers is to capture the energy from the sun and convert it into food. Plants, algae, and some bacteria are producers. Using a process called photosynthesis, producers use the sun's energy to turn water and carbon dioxide into food energy. They earn their name, because—unlike the other organisms in an ecosystem—they can actually produce their own food. Produces are the original source of all food within an ecosystem.

In most ecosystems, the sun is the source of energy that producers use to create energy. But in a few rare cases—such as ecosystems found in rocks deep beneath the ground—bacterial producers can use the energy found in a gas called hydrogen sulfide, that is found within the environment, to create food even in the absence of sunlight!


Most organisms in an ecosystem cannot make their own food. They depend upon other organisms to meet their food needs. They are called consumers—because that is what they do—consume. Consumers can be broken down into three classifications: herbivores, carnivores, and omnivores.

  • Herbivores are consumers that only eat plants. Deer and caterpillars are herbivores found commonly in a number of environments.
  • Carnivores are consumers that only eat other animals. Lions and spiders are examples of carnivores. There is a special category of carnivore called scavengers. Scavengers are animals that eat only dead animals. Catfish and vultures are examples of scavengers.
  • Omnivores are consumers that eat both plants and animals depending upon the season and availability of food. Bears, most birds, and humans are omnivores.


Consumers and producers can live together nicely, but after some time, even the vultures and catfish would not be able to keep up with all of the dead bodies that would pile up of the years. That's where decomposers come in. Decomposers are organisms that break down and feed off of the waste and dead organisms within an ecosystem.

Decomposers are nature's built-in recycling system. By breaking down materials—from dead trees to the waste from other animals, decomposers return nutrients to the soil and create another food source for herbivores and omnivores within the ecosystem. Mushrooms and bacteria are common decomposers.

Every living creature in an ecosystem has a role to play. Without producers, consumers and decomposers would not survive because they would have no food to eat. Without consumers, the populations of producers and decomposers would grow out of control. And without decomposers, producers and consumers would soon become buried in their own waste.

Classifying organisms by their role within an ecosystem helps ecologists understand how food and energy ebb and flows in the environment. This movement of energy is usually diagrammed using food chains or food webs. While a food chain shows one path along which energy can move through an ecosystem, food webs show all of the overlapping ways that organisms live with and depend upon one another.

Energy Pyramids

Energy pyramids are another tool that ecologists use to understand the role of organisms within an ecosystem and how much energy is available at each stage of a food web. Most of the energy in an ecosystem is available at the producer level. As you move up on the pyramid, the amount of available energy decreases significantly. In general, only about 10 percent of the available energy from one level of the energy pyramid transfers to the next level. the remaining 90 percent of energy is either utilized by the organisms within that level or lost to the environment as heat. 

The energy pyramid shows how ecosystems naturally limit the number of each type of organism it can sustain. Organisms that occupy the top level of the pyramid—tertiary consumers—have the least amount of available energy. Therefore their numbers are limited by the number of producers within an ecosystem.