EFE - Measuring Energy Flow Lesson

Measuring Energy Flow

How Can You Measure Energy?

What do these three pictures have in common?

Besides all being examples of aquatic life, these are ways that ecologists can track energy in an ecosystem. Ecologists use food webs, food chains, and energy pyramids to look at organism interactions within an ecosystem and how energy is passed on. Remember that ultimately all energy in an ecosystem comes from the sun, but what happens after that?

Go With the Flow

Energy must constantly flow through an ecosystem for the system to remain stable. What exactly does this mean? Essentially, it means that organisms must eat other organisms. Understanding how energy is being transferred is essential to the health of an ecosystem. Tools such as food chains, energy pyramids, and food webs are used to trace how energy travels through the different trophic levels of an ecosystem.

The trophic level of an organism is the position it occupies in a food chain and are typically identified as the following:

1. Producers
2. Primary Consumers
3. Secondary Consumers
4. Tertiary Consumers
5. Quaternary Consumer

Food chains show the eating patterns in an ecosystem and are used to show the feeding relationship between organisms and how energy is being transferred. The arrow points from the organism being eaten to the organism that eats it. For example, an arrow from a plant to a grasshopper shows that the grasshopper eats the leaves. Energy and nutrients are moving from the plant to the grasshopper. Next, a bird might prey on the grasshopper, a snake may eat the bird, and then an owl might eat the snake.

The Food Chain would look like this:

Producers are always at the beginning of the food chain, bringing energy into the ecosystem. Through photosynthesis, the producers create their own food in the form of glucose, but also create the food for the other organisms in the ecosystem. The herbivores come next, then the carnivores. When these consumers eat other organisms, they use the glucose in those organisms for energy. Decomposers can be added at any spot in the food chain to recycle matter and nutrients back into the ecosystem. Each organism can eat and be eaten by many different types of organisms, so simple food chains are rare in nature. A collection of all of the possible food chains in an ecosystem is called a food web. A food web creates a more accurate flow of energy within an ecosystem. It shows the feeding relationships between many organisms in an ecosystem. There are many more arrows, but it still shows the flow of energy, and the different paths that energy can take.

Look above at the savanna food web.

How many food chains do you think make up this food web?

There are at least 8 food chains – but you could justify more chains depending on where you start and stop them!

Energy flow decreases at each succeeding organism in a chain or web. Typically only 10% of usable energy is transferred between trophic levels. This means that if a plant has 100 units of energy, the rabbit that eats it will only be able to gain 10 units of energy.

What happened to all the energy? Some of it is used to sustain life processes for the grass and some of it is lost to entropy. The dry weight of all organic matter within the organisms of a food chain/web is called biomass. Ecological efficiency is the term that describes the percentage of usable energy transferred as biomass from one trophic level to another.

Let’s review the flow of energy in an ecosystem by watching the video below:

Ecological Pyramids

Ecological pyramids are graphic representations of the relationships between organisms and the different trophic levels. The basis of an ecological pyramid is the energy, number, and biomass of organisms. The concept of pyramids was first introduced by Charles Elton, the pioneer British Ecologist and are still used to study and visualize the use of usable energy in an ecosystem.

Measuring Energy Flow Challenge

Before You Go, You Need to Know

The following key points are from this explore section of the lesson. You must know the following information before moving to the next lesson. This is just a summary of the key points.

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