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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.

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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.This ten percent is just an estimate, because there are a lot of factors involved.

First, not all of the organism on the previous level is consumed, some of it may be left behind. Additionally, some of it is lost as waste through the consumer. And the ten percent rule is a rough estimate, for example, some organisms are more efficient at digesting than others, and some organisms are very wasteful eaters.

But, in general, the ten percent rule is accepted as an ecological rule of thumb for food chain energy transfer.

Ecological Pyramids

We can visualize the cumulative energy loss for a food chain through what is called a production pyramid. The tiers of the pyramid represent all of the chemical energy available in all of the organisms of that trophic level. The width of each tier represents how much energy from the tier below was incorporated into that trophic level as organic matter.You have probably already guessed that the base of the pyramid is made up of producers, because this is the first trophic level. This is also the widest tier, because it contains the initial energy source for all the other trophic levels.

The tier above this is made up of the primary consumers, but this level is much smaller because only ten percent of the energy from the base makes it to this level. Again, if we think of 1,000 calories making up the base of the pyramid, the primary consumer’s level would be made up of only 100 calories. The next level up is made up of the secondary consumers, and this level is even thinner than that of the primary consumers, because only ten percent of the energy from the level below it is transferred through the food chain.

We continue like this up the pyramid with each successive pier being about 90% thinner than the one before it.

Lesson Summary

Being at the top of the food chain is not the best place to be if we’re talking about energy flow, because an estimated 90% chemical energy is lost as it is transferred between each trophic level, or location in the food chain. That means only ten percent is available from one level to the next. Ecologically speaking, it is far more efficient to be closer to the producers, because these are the photosynthetic organisms that produce food for all other levels of the food chain. This trophic efficiency can be visualized in a production pyramid, which shows the cumulative energy loss for a food chain.

Each tier represents a trophic level, and the width of each level represents the amount of energy incorporated from the level below. The producers make up the base of the pyramid, which is also the widest tier.

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