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Trophic Efficiency & Ecological Pyramids: Definition & Examples

Trophic Efficiency & Ecological Pyramids: Definition & Examples
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  • 0:00 Trophic Levels
  • 2:38 Trophic Efficency
  • 4:18 Ecological Pyramids
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

If we're talking energy, being at the top of the food chain is not the place to be. In this lesson, we'll discuss how energy moves through the different levels of a food chain, and where you can get the most bang for your buck.

Trophic Levels

Every organism needs to take in nutrients to survive. For many, this involves eating other organisms. Have you heard of a food chain? This is simply how we describe food transfer through different trophic levels. And a trophic level is just the position an organism holds in a food chain. Food chains can be simple or complex, but usually they interconnect to form food webs. However, for this lesson we're just going to look at how energy - food - flows through a single food chain so that you can gain an understanding of what happens to it.

But first we need to know what the different trophic levels in a food chain are. Using a land food chain for our example, let's start at the very bottom. Here we find the producers, which are photosynthetic organisms that produce food for all other levels of the food chain. These are also known as self-feeders, because they can produce their own food from sunlight. Plants are the main producers on land, supporting the majority of other life. It's important to note that all other organisms in all other trophic levels are other-feeders, since they rely on outside sources for food. We call these consumers. So, producers produce food, while consumers consume it.

The first level of consumers in the food chain is made of primary consumers, or organisms that eat producers. Primary is for the first level. These are herbivores, so they are things that like to eat plants, like insects, mammals, birds, etc.

One level above the primary consumers are the organisms that eat primary consumers, or the secondary consumers. Again, secondary for second-level consumers. These are things like mammals, frogs, birds, spiders and even things like lions because they eat herbivorous mammals.

Can you guess what's next? Tertiary consumers are organisms that eat secondary consumers, also called 3rd-level consumers. This trophic level is one level above the secondary consumers. Most ecosystems will have both secondary and tertiary consumer trophic levels, but not all do. This level might include a snake that eats a mouse that eats an insect that eats plants. Can you see how this all comes together?

Finally, we might also find a level of quaternary consumers, or organisms that eat tertiary consumers, such as a hawk that eats a snake that eats a mouse that eats an insect that eats plants. Amazingly, in this example, the hawk is at a higher trophic level than a lion, simply because of how many organisms are in the food chain below it.

Trophic Efficiency

Your location in a food chain determines the ecological cost of your meal. Energy flows through a food chain from bottom to top, but at each trophic level you lose a certain amount. In fact, only about ten percent of the chemical energy that is available in one trophic level will be incorporated into the next trophic level. So, if you eat a salad for lunch, you're acting as a primary consumer. You are only one level removed from the producers. But if you eat a burger, then you're acting as a secondary consumer, because you're eating a primary consumer, the cow, and, believe it or not, the food energy that is available to you is actually much greater when you eat a salad than when you eat a burger.

Here's how it works. If you eat 1,000 calories of plant energy as a primary consumer, you can expect to get about ten percent of that, or 100 calories of energy. But if you are a secondary consumer, you only get ten percent of that first ten percent, so only ten calories of energy. If you are another level up, a tertiary consumer, then you only get ten percent of that, so only one calorie of energy. Not very efficient in terms of trophic energy.

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