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Energy and the Environment
All organisms need energy to stay alive. How do you get energy to run your body?
Like all organisms, the energy that powers your body comes from food.
You may be surprised to learn that sunlight is the main source of energy in most ecosystems. Why is this so? You have learned that green plants use the energy in sunlight to make food in a process called photosynthesis. During photosynthesis, carbon dioxide and water are combined to form food. The energy from the sun is stored in that food.
Plants use some of the food they make for growth and reproduction. However, extra food is stored in the plants. Animals that eat the plants use stored food in the plants for energy. Ecologists classify organisms into three major groups according to the way they get food.
Organisms that make, or produce, their own food are classified as producers . All green plants are producers. Algae are the producers in water ecosystems. How do algae and green plants make food?
The second major group of organisms is the consumers. Consumers are organisms that obtain their food by eating other organisms. Some consumers, like deer and bison eat only producers. Consumers that eat only producers are called herbivores. Consumers, such as cougars and wolves that eat other animals are called carnivores. Some organisms eat both plants and animals. These organisms are omnivores. What kind of consumer are you?
Consumers can be grouped into feeding levels according to the foods they eat.
Animals that eat plant are primary consumers. The secondary consumer is an animal the eats primary consumers. Third level consumers eat secondary consumers and so on. At what feeding level would a carnivore be classified?
Many organisms feed at more than one level. For example, bears eat berries, mice, and fish. When eating berries a bear is a primary consumer. Mice are primary consumers, so a bear eating a mouse is then a secondary consumer. For this reason, an omnivore such as a bear may occupy several different feeding levels.
The last major feeding group in an ecosystem is the decomposers. Decomposers are organisms that feed on dead organisms. In the process of feeding, decomposers break down dead plants and animals and return nutrients to the soil. Bacteria and fungi are the two most important groups of decomposers.
You can draw models to show the flow of energy from organism to organism in an ecosystem. The model of the flow of energy through the organisms of an ecosystem is called a food chain . This is an example of a food chain.
Sun ► Grass ► Mouse ► Hawk
The source of energy for the food chain is the sun. The arrows represent the flow of energy through the ecosystem. The arrows always point in the direction energy is flowing. On important fact to remember about food chains is that the energy that flows
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Name_____________________________________ Date_____________ Hour________ through the ecosystem is not recycled. Sunlight must continue to flow into the biosphere to supply energy for food chains.
Most plants and animals are involved in many food chains. In ecosystems, many food chains combine and overlap to form a food web . A food web includes more information about the flow of energy in an ecosystem than a food chain. For this reason, a food web is a better model of energy flow in an ecosystem than individual food chains
In a food chain producers capture sunlight energy and store it in food. When a consumer eats a producer, it contains only a small amount of the energy from that producer. The same is true for each link in the food chain.
Animals gain only a mall amount of the energy from the food they eat. The rest of the energy is used up or is released as heat energy. A model called an energy pyramid show that the amount of energy decreases at each level of the food chain. As a result, fewer organisms can be supported at each level. There are fewer predators at the top of the food chain compared with the number of prey organisms. What do you think would happen if the number of predators in an area was greater than the number of prey?
The organisms in an ecosystem are involved in relationships with other organisms and the physical environment. Some of these relationships help organisms survive. Other relationships however, make life more difficult for organisms.
You often hear that athletes are competing in a game. In the science of ecology, competition means organisms striving for the same thing. Competition makes survival more difficult.
Animals compete for resources such as food, cater, shelter, territory, and mates. Plant competition is less active than animal competition, but it is just as important. For example, plants compete for sunlight, water and growing space.
In some relationships, one kind of organism feeds upon another organism. In predation one organism kills and eats the other. A relationship in which an organism lives on or in another living organism is called parasitism . A parasite is an organism that takes its nourishment from a living organism called the host.
Ticks, fleas, and leeches are examples of parasites that live outside a host. These parasites feed upon the blood of their hosts. Most parasites, however, live within their hosts. For example, a tapeworm is a parasite that lives in the digestive tract of its host.
Many types of worms, fungi, and microorganisms live inside other organisms.
While parasites may eventually weaken or kill their hosts, predators capture and kill their prey before eating it. Wolves, feeding upon caribou, are an example of predation. It is easy to see that wolves benefit from this relationship because they eat the caribou.
What is not easily noticed is that the caribou herd also can benefit from predation.
How do the caribou benefit from predation? Wolves will capture weak or diseased caribou more easily than strong, healthy ones. Because diseased or less-fit members are removed from the herd, the caribou herd is kept strong and healthy. Predation by wolves also may help prevent overpopulation of the caribou herd.
Some relationships in the environment make survival easier. An example of a helpful relationship is mutualism . Mutualism is a relationship between two different kinds of organisms that benefits both organisms. For example, when bees obtain food by
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Name_____________________________________ Date_____________ Hour________ gathering nectar from flowers, they also pollinate the flowers. Both bees and flowers gain from this interaction. What is the benefit to the bees?
In commensalism , one organism benefits from the relationship while the other is unaffected. Orchids growing on trees in tropical forests demonstrate commensalisms.
The orchid grows attached to the tree but does not take nourishment from the tree. The orchid takes everything it needs to grow and survive from the air. The orchid benefits by having a place to grow. The tree is not affected in any way.
All the relationships in an ecosystem help to keep the ecosystem in balance. Natural disasters such as floods or fires may upset the balance in ecosystems. It may take years, but an ecosystem usually will regain its balance after a natural disaster.
People often change and upset the balance of ecosystems, too. For example, people may remove most of the predators in an ecosystem. This may result in overpopulation of the herbivores upon which they prey. As a result, the herbivores may run out of food and begin to starve. Parasites also can spread more rapidly in the crowded herbivore population.
Most organisms that you consider pests were in balance in ecosystems until people disturbed that balance. For example, by planting huge fields of cotton, farmers created a perfect environment for the boll weevil, which then overproduced and became a pest.
Cockroaches and rats were carried in ships to areas where they were not originally found.
Cities provided these two organisms with ideal growing conditions, and they have become widespread pests.
Questions
1.
What do ecologists call organisms that can make their own food?
2.
Where do producers get their energy?
3.
What kind of diagram shows the amount of energy available at each food level in an ecosystem?
4.
Why is a food web a better representation of the flow of energy in an ecosystem than a food chain?
5.
How do consumers benefit from photosynthesis?
6.
In an energy pyramid, why are their fewer predators than prey?
7.
Name the kind of relationship between organisms in which both organisms gain from the relationship.
8.
Both predators and parasites get nourishment from other organisms. How are they different?
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9.
Explain how wolves keep the caribou herd in balance.
10. List three ways that people can upset the balance in an ecosystem.
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