Energy Flow and the 10 Percent Rule

Energy Flow and the 10 Percent Rule

On average only 10 percent of energy available at one trophic level is passed on to the next. This is known as the 10 percent rule, and it limits the number of trophic levels an ecosystem can support.


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Biology, Ecology

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Living things need energy to grow, breathe, and reproduce. They get this energy from an ecosystem.

An ecosystem is like a community that is made up of all the living and nonliving things in an area. These include soil, plants, animals, and insects.

The sun is the first source of energy for an ecosystem. Energy from the sun is called solar energy. Living things, or organisms, like plants turn solar energy into biomass. This is the energy that is part of living organisms.

As organisms eat other organisms, the biomass, or energy, is transferred all the way up through the food chain. A food chain is a path that energy takes through an ecosystem.

Organisms Are Part of Food Chains

Each organism in an ecosystem is part of many food chains. The organisms are grouped into categories called trophic levels. They are categorized based on how they obtain food.

Organisms in the first trophic level in any ecosystem are called primary producersProducers are organisms that produce their own food. Plants, like grass, are common primary producers. These organisms use photosynthesis to create nutrients from sunlight, carbon dioxide, and water. This process is how plants convert solar energy into biomass.

Organisms in the second trophic level are called primary consumersConsumers are organisms that can't produce their own food and therefore rely on eating other organisms to get energy. These organisms eat primary producers. They include herbivores and omnivores. Herbivores are animals that only eat plants. Omnivores are animals that eat both plants and animals.

Secondary consumers make up the third trophic level. These organisms are either omnivores or carnivores. Carnivores are animals who only eat other animals. Secondary consumers eat primary consumers.

The fourth trophic level contains tertiary consumers. These carnivores or omnivores hunt secondary consumers.

This is a simplified model. In reality, many different organisms would eat plants, not just grasshoppers. Tertiary consumers would need to hunt many different animals to survive. Most ecosystems are more complex, and they would be better represented by a connected series of food chains known as a food web.

Five Trophic Levels

Five is the maximum number of trophic levels that most ecosystems can support, but some food chains are smaller. This is because only so much biomass, or energy, can move from one trophic level to the next. Energy is lost at each step along the food chain.

In an ecosystem, energy transfer begins with the primary producers. Only a fraction of all the solar energy that reaches Earth lands on plants. Not all of that solar energy is the right kind of sunlight that can fuel photosynthesis. So, plants do not use all the sunlight that hits them.

Once the producer">primary producer converts the solar energy into fuel, it needs some of this energy for itself, so that it can breathe and grow. Only the leftover energy can be used by consumers.

Lower trophic levels have more biomass, or energy, than higher ones. More and more energy is lost as you move up the trophic levels. Usually, this energy is lost as heat or waste. For example, some of the energy used at each level can't be digested. It is expelled as waste. A lot of energy also escapes as heat during breathing.

In addition, plants and animals may die a natural death. A predator does not eat them. So, their biomass does not get passed to the next consumer. That energy is not passed up the food chain.

Waste and dead matter are broken down by decomposers. The resulting nutrients are recycled into the soil to be reabsorbed by plants. But the majority of the energy is lost as heat during this process.

Energy Loss

An energy pyramid is a good way to show energy loss between trophic levels. Each step of the pyramid represents a different trophic level. The primary producers are at the bottom level. The tertiary consumers are at the top level.

The size of each step corresponds to how much energy moves between levels. The steps decrease in size as you travel up the pyramid. This is because energy is lost at every level in the food chain. Eventually, the steps can't get any smaller. This means there is no energy available to support another trophic level.

Only 10 percent of energy moves from one trophic level to the next. This is known as the 10 percent rule. It limits the number of trophic levels an ecosystem can support. For example, when a primary consumer eats a primary producer the consumer only gets 10 percent of the producer's energy. So, if an insect eats a plant, it only gets 10 percent of the energy from the plant. The next consumer would only receive 10 percent of the energy from the insect. This continues all the way up the food chain.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Tyson Brown, National Geographic Society
National Geographic Society
Production Managers
Gina Borgia, National Geographic Society
Jeanna Sullivan, National Geographic Society
Program Specialists
Sarah Appleton, National Geographic Society, National Geographic Society
Margot Willis, National Geographic Society
Clint Parks
Roza Kavak
Last Updated

October 19, 2023

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