An energy pyramid shows the distribution of energy among trophic levels.

Producers use energy from sunlight to make food. Herbivores eat plants—the producers—to get energy. Some of the energy is used by the animals to grow and some is used for cellular respiration. However, most of the energy that is consumed is lost as heat. Carnivores then eat the herbivores. And again, most of the energy is lost as heat.

An energy pyramid is a diagram that compares the energy used by producers, primary consumers, and other trophic levels. In other words, an energy pyramid shows how much energy is available at each trophic level. Energy is lost at each trophic level of a food chain. Because of this, a typical energy pyramid has a large base of producers. Each level above gets smaller, because as energy is lost as heat, there is less energy avail-able as food for organisms. The longer the food chain, the more energy is lost between the bottom and top links.

Pyramid ModelsKEY CONCEPT Pyramids model the distribution of energy and matter in an ecosystem.

SECTION

13.6Student text pages 417–419

energylost as heat

energy transferred

Where are producers located on the energy pyramid?

An energy pyramid shows the energy fl ow between trophic levels in an eco-system. Between each level, up to 90 percent of the energy is lost as heat into the environment.

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Other pyramid models illustrate an ecosystem’s biomass and distribution of organisms.

An energy pyramid shows energy loss at each trophic level. Pyramid diagrams can also be used to represent other components of an ecosys-tem. Two other types of pyramid models are a biomass pyramid and a pyramid of numbers.

Biomass PyramidsBiomass is a measure of the total amount, or dry mass, of organisms in a given area. A biomass pyramid is a diagram that compares the biomass of different trophic levels within an ecosystem. It shows the mass of producers that are needed to support primary consumers, the mass of primary consumers required to support secondary consumers, and so on. Notice that each trophic level has a smaller biomass than the one below it.

The prefix bio- refers to life or living things. Mass is a measurement of the amount of matter. Biomass is a measure-ment of the amount of living organisms in an area.

VOCABULARY

The biomass pyramid shows the total dry mass of organisms found at each trophic level.

primaryconsumers

secondaryconsumers

tertiaryconsumers

675 g/m2

150 g/m2

75 g/m2

producers 2000 g/m2

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Pyramids of NumbersA pyramid of numbers gives a count of the numbers of individual organ-isms at each trophic level in an ecosystem. This type of pyramid gives a good picture of the large numbers of producers that are required to support just a few top-level consumers. Notice that it takes a huge number of producers to support just a few mountain lions.

What is represented by a pyramid of numbers?

biomass

energy pyramid

1. What is represented by an energy pyramid?

2. What is represented by a biomass pyramid?

3. Which trophic level contains the most energy?

4. What happens to most energy at each trophic level?

13.6 Vocabulary Check

Go back and highlight each sentence that has a vocabulary word in bold.

Mark It Up

13.6 The Big Picture

primaryconsumers

secondaryconsumers

tertiaryconsumers

500,000

5000

5

producers

In a pyramid of numbers, each level represents the actual number of organisms at each trophic level.

5,000,000

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What is represented by a pyramid of numbers?

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