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Ecosystems are comprised of a community of organisms that interact with one another. Organisms depend on each other for food. The food supplies energy needed to carry out the biological processes that are required each day. Organisms are made of matter, so within ecosystems, you can begin to see a relationship between energy and matter. Because organisms are made of matter, they have energy trapped within them. If you remember from Lesson 1.02, chemical energy is the energy trapped within the bonds of matter. This means that all living things have the potential to be a source of energy for other living things.
To better see the relationship between energy and matter, scientists often represent the energy and biomass present in an ecosystem in the form of an ecological pyramid or energy pyramid.
About Pyramids
Energy pyramids are used to show how much energy is available in each of the different trophic levels. Because the amount of energy is proportional to the amount of matter in an ecosystem, these pyramids can also show how much matter or biomass is available in each trophic level. When you examine an energy pyramid, you see that the base of the pyramid is bigger than the levels above it, and each individual level is smaller than the one below. The base is always bigger because this makes the entire structure stable.
Energy pyramids are set up with the organisms with the most available energy at the bottom.
- The first level is the producer trophic level.
- The second level is made up of the primary consumers.
- The third level is the secondary consumers, and
- the fourth level is the tertiary consumers.
Therefore, it can be stated that there are a greater number of organisms that are producers than there are the number of tertiary consumers. If something occurs where there are more primary consumers than producers, an ecosystem becomes unstable and likely to have problems or even collapse. More primary consumers than producers could mean that the primary consumers will deplete all of the energy resources/food available to them. When this happen, the primary consumers will begin to die off creating less food and energy available for the secondary consumers. Unless stopped, this will eventually affect the tertiary consumers and the whole ecosystem could disappear.
Energy Pyramids
An energy pyramid shows energy in an ecosystem. The bottom layer has plants and other producers. Producers are organisms that make their own food. The middle layer has herbivores. They eat plants and other producers. The word herbivores means plant eater. The top layer has types of carnivores. They eat herbivores. They may even eat other carnivores! The word carnivore means meat eater. In a healthy ecosystem, there are lots of producers, and some herbivores, but not many carnivores.
Let's look at a forest energy pyramid.
Trees are producers. They capture energy from the sun. They turn the energy into sugar - a form of food, they can use and store. Food provides energy for living things.
Caterpillars are herbivores. They get the sugar stored in the plant when they eat it. It gives them energy to move and grow. They use most of the energy, but they store some of it.
What eats the caterpillars? Birds do. They get energy from the caterpillars - but not all the energy that came from the plants. The caterpillars used some of that energy. On each step of the pyramid, some of the energy is lost.
What would happen if there were as many birds as there are caterpillars? The birds would be hungry. It take a lot of caterpillars to feed one bird. For an ecosystem to be healthy there cannot be too many organisms at the top of the pyramid.
Let's look at a prairie grassland energy pyramid.
Grasses are producers. Like other plants, they make their own food using light from the sun.
Prairie dogs eat seeds and grass. They are herbivores. They only eat producers, like plants. They get their energy from the plants.
Coyotes, on the other hand, are carnivores. They eat prairie dogs.
What if there were no coyotes? What if nothing ate prairie dogs? There could be a lot of prairie dogs! A lot of hungry prairie dogs could eat a lot of plants! That could be bad news for the ecosystem.
Carnivores, like the coyote, can help keep the ecosystem in balance.
Let's look at an ocean energy pyramid.
These plankton are producers. Like plants, they capture energy from the sun to make food.
Krill eat the plankton. That's how they get the energy they need to move and grow. They use some of the energy and they store some.
Fish eat the krill. They are carnivores.
So energy goes from the sun to the plankton to krill to the fish. A little energy is lost at each step.
What if something happens to the bottom layer of the pyramid? There would be no food for the krill. And then no food for the fish. And no food for other things that eat fish.
Changes in energy in a ecosystem can make a big difference
Available Energy
Not all of the energy in a trophic level is available to the level above it. About 90% of the energy in a trophic level is used by the organisms in that level for biological process, such as growth, reproduction, and hunting. This means that only about 10% of the energy in a trophic level is available to the next level above it. This is the case for each trophic level. This is why the number of individual organisms is lower than the trophic level below it.
To get an estimate of how much energy in one trophic level is available to the next trophic level, you multiply the amount of energy (expressed in Joules) by 0.10. This will show you the approximate amount of available energy.
Available Energy= Energy X 0.10. So if there are 10,000 J of energy located in the producers level of an ecosystem, you would do the following: 10,000 X 0.10= 1,000 Joules of energy that can be passed to the primary consumers. How much energy would be available to the secondary consumers? 1,000 X 0.10= 100 Joules.
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