Unit A Lesson A5 Energy Flow in Ecosystems
Completion requirements
Lesson A5: Energy Flow in Ecosystems
Video Lesson
Energy flows in complex ways in ecosystems. Watch this video to learn more about how energy moves from organism to organism.
Lesson A5: Energy Flow in Ecosystems
How Big is an Ecosystem?
An ecosystem has almost no size limit. It can be as big as the planet itself. It can be so small you need a microscope to see it. A large ecosystem can be made of many smaller ones.
An ecosystem has almost no size limit. It can be as big as the planet itself. It can be so small you need a microscope to see it. A large ecosystem can be made of many smaller ones.
Reading and Materials for This Lesson
Science in Action 7
Materials:
Science in Action 7
Reading: Pages 35–42
Materials:
No other materials are needed for this lesson.
Energy Starts from the Sun and Flows through Ecosystems
Every organism, from an alpine flower to a vole to a cougar, relies on the Sun’s energy to live. Plants use sunlight to make food through photosynthesis. Do cougars need plants? After all, they eat meat, not plants. You might be surprised to learn that plants determine every aspect of the cougar’s life.
When organisms consume other organisms, energy is transferred through an ecosystem. All organisms depend on other organisms for food energy. The energy is transferred upward through a food chain. Food chains connect with other food chains to make food webs. In Lesson A4, you constructed food chains and a food web for an Alberta wetland ecosystem. Plants and animals in any ecosystem form many connections. Every connection is based on food energy.
Every organism, from an alpine flower to a vole to a cougar, relies on the Sun’s energy to live. Plants use sunlight to make food through photosynthesis. Do cougars need plants? After all, they eat meat, not plants. You might be surprised to learn that plants determine every aspect of the cougar’s life.
When organisms consume other organisms, energy is transferred through an ecosystem. All organisms depend on other organisms for food energy. The energy is transferred upward through a food chain. Food chains connect with other food chains to make food webs. In Lesson A4, you constructed food chains and a food web for an Alberta wetland ecosystem. Plants and animals in any ecosystem form many connections. Every connection is based on food energy.
Figure A.2.5.1 – Plants are the support system for all other organisms that live in this alpine meadow.
Figure A.2.5.2 – An alpine vole gathers plants and seeds to eat during the winter.
Figure A.2.5.3 – A cougar needs a lot of energy to grow and live.
One Big Energy Drain!
Cougar prefer elk and deer. In a pinch, though, a fox snack will sustain the cougar for a few days. The cougar is the top predator here, but it is at the losing end of its food chain. Organisms at the tops of food chains obtain only a small fraction of the food energy available at the bottom.
In every food chain, energy flows from producers to consumers to decomposers. At every level of the chain, energy is lost in many ways. If the cougar catches the fox, it will obtain only about one-tenth (1/10) of the energy produced by the fox.
Nine-tenths of the fox’s energy is lost before the cougar can eat it. The fox loses energy as body heat. It loses energy because, as with all animals, some of the food it eats is not digested. Then, the fox uses energy to hunt for voles. It uses energy to grow and stay healthy. In every living organism, energy is used and energy is lost.
It takes a lot of energy to breathe, grow, stay warm, move, and reproduce. Most of a food chain’s energy is used in the process of living.
Cougar prefer elk and deer. In a pinch, though, a fox snack will sustain the cougar for a few days. The cougar is the top predator here, but it is at the losing end of its food chain. Organisms at the tops of food chains obtain only a small fraction of the food energy available at the bottom.
In every food chain, energy flows from producers to consumers to decomposers. At every level of the chain, energy is lost in many ways. If the cougar catches the fox, it will obtain only about one-tenth (1/10) of the energy produced by the fox.
Nine-tenths of the fox’s energy is lost before the cougar can eat it. The fox loses energy as body heat. It loses energy because, as with all animals, some of the food it eats is not digested. Then, the fox uses energy to hunt for voles. It uses energy to grow and stay healthy. In every living organism, energy is used and energy is lost.
It takes a lot of energy to breathe, grow, stay warm, move, and reproduce. Most of a food chain’s energy is used in the process of living.
This food chain starts with plants and seeds. A vole eats them. Then, an arctic fox eats the vole. Finally, a cougar eats the fox. The cougar gets only a thousandth of the energy produced originally by the plants. This is why food chains rarely are longer
than four or five links. The energy available to organisms simply is used up. What do you think this means for the number of cougars at the top of the food chain? Think about your answer as you read on.
All food chains, from arctic to desert to ocean chains, have something in common. Plants produce all the energy in any food chain. In addition, they contain most of the chain’s energy that is available as food.
What does this mean for our arctic food chain? To support just one cougar, the food chain must contain a lot of plants. A typical cougar’s range is very large, about 150 square kilometres. It needs to hunt over its entire range to kill enough prey to eat.
All food chains, from arctic to desert to ocean chains, have something in common. Plants produce all the energy in any food chain. In addition, they contain most of the chain’s energy that is available as food.
What does this mean for our arctic food chain? To support just one cougar, the food chain must contain a lot of plants. A typical cougar’s range is very large, about 150 square kilometres. It needs to hunt over its entire range to kill enough prey to eat.
Figure A.2.5.4 – This arctic fox smells a vole nearby.
Figure A.2.5.5 – About 90% of the energy in a food chain is lost at every level. Hardly any original plant energy is available to the cougar.
That is a lot of land and a lot of plants for just one cougar!
What do plants have to do with cougars and their prey? Look at the numbers for the answer. Enough plants to feed a thousand voles might be available in the cougar’s range. Those voles might be enough to feed just ten foxes. Just a few of those foxes might become cougar food.
Because this is a simplified example of food chain, knowing the exact numbers is difficult. Foxes eat many animals in addition to voles. The cougar hunts mostly mule deer and elk that roam through its range, too.
Relationships may be complex, but the central point is clear. The cougar relies on the plants in its food chain although its relationship to them is indirect. In all food chains, one key trend is clear: food chain energy always looks like a pyramid.
What do plants have to do with cougars and their prey? Look at the numbers for the answer. Enough plants to feed a thousand voles might be available in the cougar’s range. Those voles might be enough to feed just ten foxes. Just a few of those foxes might become cougar food.
Because this is a simplified example of food chain, knowing the exact numbers is difficult. Foxes eat many animals in addition to voles. The cougar hunts mostly mule deer and elk that roam through its range, too.
Relationships may be complex, but the central point is clear. The cougar relies on the plants in its food chain although its relationship to them is indirect. In all food chains, one key trend is clear: food chain energy always looks like a pyramid.
Figure A.2.5.6 – The fox must beware. To a hungry cougar, the fox might look like a tasty snack.
Figure A.2.5.7 – Roughly 10% of energy in any food chain flows from one level to the next. Energy loss forms a pyramid shape.
The Energy Pyramid
To get a good idea of the functioning of food chains, food webs, and energy pyramids, explore this online interactive: Taiga Food Web. Here, you will learn about how energy moves within a taiga (or boreal) ecosystem.
Plants form the widest base. Stacked on that base are primary consumers, then secondary consumers, and so on. At the top of the pyramid usually is only one or two individuals. In any ecosystem, the top or apex predators, such as the cougar, are few.
To get a good idea of the functioning of food chains, food webs, and energy pyramids, explore this online interactive: Taiga Food Web. Here, you will learn about how energy moves within a taiga (or boreal) ecosystem.
Plants form the widest base. Stacked on that base are primary consumers, then secondary consumers, and so on. At the top of the pyramid usually is only one or two individuals. In any ecosystem, the top or apex predators, such as the cougar, are few.
The energy pyramid provides valuable information about how energy flows in a food web. However, sometimes the picture is not clear. If you look to the examples in
Lesson A4, you can find two cases where an energy pyramid would be difficult to construct.
The first case is the soil food web. To assign a food chain level to decomposers is difficult although they are part of the food chain’s energy. Decomposers consume dead plant and animal material. By doing so, these organisms obtain energy at every level of the pyramid.
The second case is the food web you constructed. Some organisms fit into more than one energy level, depending on what they eat. For example, the lynx is a predator that consumes many prey. It can be a secondary or higher level consumer, depending on what it eats. Other organisms change levels as they grow. The female mosquito in your food web is an example. Its food changes as it matures. It changes from a primary consumer to a higher level consumer.
The first case is the soil food web. To assign a food chain level to decomposers is difficult although they are part of the food chain’s energy. Decomposers consume dead plant and animal material. By doing so, these organisms obtain energy at every level of the pyramid.
The second case is the food web you constructed. Some organisms fit into more than one energy level, depending on what they eat. For example, the lynx is a predator that consumes many prey. It can be a secondary or higher level consumer, depending on what it eats. Other organisms change levels as they grow. The female mosquito in your food web is an example. Its food changes as it matures. It changes from a primary consumer to a higher level consumer.
Figure A.2.5.8 – Some living things, like the lynx, can fit in more than one place on an energy pyramid.
Watch More
The Base of the Arctic Marine Food Pyramid: Algae
That tiny microscopic algae power an entire food web topped by seals, beluga whales, and polar bears might be difficult to believe. Yet, that is exactly what they do in the Arctic Ocean.
In this video, researchers are exploring life in, on, and under sea ice. The frozen ocean looks barren, but it teems with life. It is a wonderful example of an arctic energy pyramid.
As you watch this video, ask yourself the following questions.
That tiny microscopic algae power an entire food web topped by seals, beluga whales, and polar bears might be difficult to believe. Yet, that is exactly what they do in the Arctic Ocean.
In this video, researchers are exploring life in, on, and under sea ice. The frozen ocean looks barren, but it teems with life. It is a wonderful example of an arctic energy pyramid.
As you watch this video, ask yourself the following questions.
- What organism forms the base of this arctic energy pyramid?
- Which seasonally changing abiotic factors affect the growth rate of the algae?
- The video mentions various large marine animals in this ecosystem. On which single organism do they all rely for energy?
- In the video, a jellyfish is pulled up in the net. What role does it have in this ecosystem?
- Why do the researchers want to monitor the algae in this ecosystem?
Try It!
Build an Energy Pyramid
Try this experiment at home to demonstrate how energy flows through a southern Alberta grassland ecosystem.
Materials:
Try this experiment at home to demonstrate how energy flows through a southern Alberta grassland ecosystem.
Materials:
- copy of the “Build an Energy Pyramid” activity (including template you will need to print out).
- energy pyramid template (with 4 levels)
- pencil
- sheet of paper
Download:
DOWNLOAD this document. It provides a space for you to write answers to questions later in this activity. It also has an energy pyramid template for you to print out.
Instructions:
DOWNLOAD this document. It provides a space for you to write answers to questions later in this activity. It also has an energy pyramid template for you to print out.
Instructions:
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Print the energy pyramid template.
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On the left side of the template, label each energy level as producer, primary consumer, secondary consumer, or tertiary consumer.
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On the right side of the energy pyramid template, label each energy level as Level 1, Level 2, Level 3, and Level 4.
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Read the Species List below very carefully. Give special attention to what each species consumes.
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Decide into which level each organism in the Species List fits. Write the species name in that level of your pyramid.
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Give your completed energy pyramid an appropriate title.
- You will notice that some species might not fit into the energy pyramid. Make a list of them on a separate sheet of paper. As you do so, make a note beside its name of the role of each species and what it eats.
Species List:
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Your Alberta grassland energy pyramid should look something like this when you are finished.
Soil microbes and earthworms are both decomposers. They seem not to fit in the pyramid. Or do they? Look back to the soil ecosystem example in Lesson A4 for clues. You can argue that another producer in this ecosystem is dead plant material. You can add
it to Level 1. Soil microbes and earthworms consume this material, so they are primary consumers. You can add them to your pyramid at Level 2.
The soil microbes also consume dead animal material. In this role, they consume energy from all four levels of the pyramid. You cannot place them in one particular level. However, you can draw arrows leading off each level to soil microbes to indicate that some energy flows to them. You can see how this was done in the energy pyramid diagram earlier in this lesson.
The soil microbes also consume dead animal material. In this role, they consume energy from all four levels of the pyramid. You cannot place them in one particular level. However, you can draw arrows leading off each level to soil microbes to indicate that some energy flows to them. You can see how this was done in the energy pyramid diagram earlier in this lesson.
This is a fairly simple calculation. If the grasses produce 1000 KJ of energy, the grasshoppers and prairie dogs can obtain 100 KJ (1/10) of that energy. The ferruginous hawks and black-footed ferrets can obtain 10 KJ (1/100) of that energy. The great
horned owls can obtain only 1 KJ (1/1000) of that energy. You can put these energy amounts in your pyramid to show how much energy is lost.
Hawks and ferrets have ten times more total energy available to them than owls have. Assume that an owl needs the same amount of food energy as either the hawk or the ferret does. (The owls are actually larger animals, so they likely need more food.)
For every 10 ferrets or hawks, only one owl can be supported in this ecosystem.
This is another fairly simple calculation. You know from your earlier answer that the owl’s energy level receives only 1/1000 of the total plant energy. That means 1 KJ of energy is available. This supports only one owl. Therefore, each owl needs a territory
of about 10 square kilometres.
The territories of great horned owls have been studied across North America. Ecologists use these kinds of calculations to determine how much land the animals need. In the Yukon Territories where vegetation is poor and winters are long, this owl’s territory is 16 square kilometres. Along some of the Columbia River in Washington state where plant life is plentiful, the owl’s territory is as small as 1 square kilometre. The owls there can switch to other plentiful primary consumers such as various rodents, rabbits, and small birds.
The territories of great horned owls have been studied across North America. Ecologists use these kinds of calculations to determine how much land the animals need. In the Yukon Territories where vegetation is poor and winters are long, this owl’s territory is 16 square kilometres. Along some of the Columbia River in Washington state where plant life is plentiful, the owl’s territory is as small as 1 square kilometre. The owls there can switch to other plentiful primary consumers such as various rodents, rabbits, and small birds.
Many abiotic factors affect how much energy the grasses can produce. Soil nutrient level is important. A richer soil produces healthier larger grass plants. Water is important. A year of drought stunts grass growth, and all other species suffer as a result.
Climate extremes affect grass growth. A hail storm or fire could destroy the grass. Some of the animals might starve or move to other territories.
Watch More
Figure A.2.5.9 – A black-footed ferret lunges after an unsuspecting prairie dog. Photo by
USFWS Mountain-Prairie.
The Endangered Black-footed Ferret
All the species in the grassland ecosystem have specific habitat requirements. Construction of roads, farms, industry, or housing can disrupt those habitats. Unfortunately, this food chain was once abundant across the prairies, but now rarely is encountered.
During the past century, farming and ranching throughout North American grasslands disrupted many black-tailed prairie dog towns. Their burrows were destroyed. The prairie dog population plummeted, but the species was not endangered. Black-footed ferrets, however, eat only prairie dogs. Their specialized diet made this species vulnerable. When prairie dogs disappeared, the ferrets were headed for extinction. Fortunately, people realized the difficulty faced by this species. They began to work to save them. Today, about 1500 black-footed ferrets survive in the wild.
Watch this video to see how wildlife experts in Arizona work to save the endangered black-footed ferret.
All the species in the grassland ecosystem have specific habitat requirements. Construction of roads, farms, industry, or housing can disrupt those habitats. Unfortunately, this food chain was once abundant across the prairies, but now rarely is encountered.
During the past century, farming and ranching throughout North American grasslands disrupted many black-tailed prairie dog towns. Their burrows were destroyed. The prairie dog population plummeted, but the species was not endangered. Black-footed ferrets, however, eat only prairie dogs. Their specialized diet made this species vulnerable. When prairie dogs disappeared, the ferrets were headed for extinction. Fortunately, people realized the difficulty faced by this species. They began to work to save them. Today, about 1500 black-footed ferrets survive in the wild.
Watch this video to see how wildlife experts in Arizona work to save the endangered black-footed ferret.
The Importance of Photosynthesis
Plants are the basis of almost every food web on Earth. They form the base of the energy pyramid. They supply energy to all other organisms in each food chain. The secret behind the essential role of plants is photosynthesis.
Explore this amazing process further by clicking the link this interactive NOVA presentation.
Explore this amazing process further by clicking the link this interactive NOVA presentation.
Illuminating PhotosynthesisNext, try this fun online photosynthesis game (the website requires free registration, if you don't want to register, that's OK, trying this game is optional):
Photosynthesis
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.
Unit A Lesson 5 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
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REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Self-Check Time!
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Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
At every level, energy is lost as heat and waste. In addition, energy is used in the process of living. Only about 1/10 of the energy is stored as body tissue. Organisms that consume that tissue obtain only about 1/10 of that level’s energy.
Most of the energy is lost at every level in a food chain. Most chains cannot support more than four or five links before available energy is depleted.
A food chain is a line of organisms linked by who eats whom or what. A food web consists of an interconnected web of food chains.
The black-footed ferret is especially vulnerable because it relies for food almost entirely on only one species. When that species, the black-tailed prairie dog, was threatened, the ferrets starved. They had no other prey as an alternate food.
Some other species are vulnerable for the same reason, such as pandas and koala bears. Pandas eat only bamboo. Koalas eat only eucalyptus leaves. Specialization can become a problem.
Decomposers consume dead organisms at every level of the energy pyramid. They obtain energy from every level of the ecosystem. This means they cannot be placed at one specific energy level.