g5 lsr 1g 5.05 interactions in ecosystems

8/12/2019 G5 LSR 1G 5.05 Interactions in Ecosystems

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Vocabulary community

cycle

ecosystem

energy pyramid

habitat

niche

population

Interactions in Ecosystemsby Patricia Fitzhugh



A community is a bigger part of an ecosystem. Acommunity is all the populations in an area. Members of acommunity depend on each other for food and shelter.

The nonliving parts of an ecosystem include air, water, soil,sunlight, and temperature. These things often control whatkinds of organisms—and how many—can live in an ecosystem.

If a population’s needs are not met in an ecosystem, thatpopulation will get smaller. Its members may not survive.

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What is an ecosystem?Living and Nonliving Parts

Wherever there are living things, there are ecosystems. Anecosystem is all the living and nonliving things in an area.

Living and nonliving things work together in ecosystems.A population is all the organisms of one species living in anarea at the same time. This may be all the oak trees. It may beall the red ants.

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BiomesA biome is a large ecosystem. Biomes are so large

that a single one may cover many countries. Theclimate and organisms are generally the same in allparts of the biome.

There are several kinds of biomes. One kind is a

rainforest. A rainforest biome has large amounts ofrain and thick plant growth.

The United States has a rainforest biome in thestate of Washington. This rainforest is a temperaterainforest. It receives a lot of rain, but can bequite cool.

Each living thing in an ecosystem has a niche.A niche is an organism’s role in an ecosystem. Forexample, the spotted owl has a niche in the temperate

rainforest. It is a hunter. The owl hunts and eats smallanimals, such as mice.

Each living thing also has a habitat. A habitat iswhere an organism lives. The spotted owl’s habitats arethe trees and land where it lives.

All the relationships in an ecosystem keep itbalanced. For example, the populations ofmice and spotted owls balance each other.It works like this:

If the number of mice drops, the owls will haveless food. So, the number of owls will drop, too. Withfewer owls hunting, fewer mice will be eaten. So, thepopulation of mice will grow. Then owls will havemore mice to hunt. So, the population of owls willgrow again.

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Grassland BiomesGrasslands are biomes with many

types of grasses. Grasslands do not getmuch rain. So few trees can grow inthese biomes.

Grasslands once covered huge

areas of the midwestern United States.Then settlers came. Over many years,settlers turned most of the grasslandsinto farms.

Bison, antelope, and prairie dogslive on the grasslands. The changingof this habitat into farms has affectedanimal populations. For example,gray wolves once hunted prairie dogs.

Farming reduced the prairie dogpopulation, so the wolves had less toeat. People also hunted the wolves.These changes caused the gray wolfpopulation to fall very low.

Taiga BiomesA taiga is a kind of forest biome.

Tiagas are found in areas that arecold and fairly dry. They cover muchof Canada and Russia.

Most trees that grow in the taiga

have very thin leaves called needles.Needles help trees live where it is cold,dry, or both. They stay on the tree allyear long so they are ready to makefood as soon as warm weather arrives.They have a waxy coating that helpsthe tree hold water.

Large animals such as bear, elk,and moose live in the taiga. Smaller

animals such as porcupines and micelive there as well. All these animalshave fur. It keeps them warm. Ducks,owls, and woodpeckers also live in thetaiga. These animals have feathers tohelp keep them warm.

Gray wolves once livedover most of North

America. Now wolveslive in only a small partof this area.

The moose is a very large animalfound in the taiga.

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Desert BiomesDeserts are areas that get less than

25 cm of rain or snow each year.All deserts have low rainfall. Manydeserts are very hot, but others arecold most of the time. Some deserts

have sand dunes and others are veryrocky. Large deserts are found inAfrica, Asia, and Australia.

Desert animals may includerattlesnakes, lizards, jackrabbits, andbeetles. Plants may include bushes,grasses, and cactuses.

Desert plants have special partsthat help them live without much

water. Some have large root systemsclose to the surface of Earth.These roots can take inrainwater quickly.

Desert animals havespecial behaviors thathelp them survive. Manyanimals rest during thehot day. Some animals dig

into the ground to keep cool.They look for food at night,when it is cooler.

Tundra BiomesThe tundra is a very cold biome. It

gets little rain. Tundras lie in the farnorthern parts of the world. Rodents,rabbits, and caribou live on thetundra. Tundra animals may also

include weasels, owls, and foxes.In any ecosystem, a population

can only grow so large. The numberof organisms that can live in aplace is the carrying capacity. If apopulation grows larger than thecarrying capacity, there won’t beenough food, water, space, or shelter.

Populations will have to

move to another area tosurvive.

On the tundra, coldweather makes it hard forplants to grow. The smallplants that do grow cannotprovide enough food andshetler for animals. Thiskeeps the carrying capacity

low.

Emus are foundin many areas of

Australia, includingdeserts.

When snow covers the tundra,caribou often move to warmerareas to find food.



Coral ReefsCoral reefs are

home to many typesof organisms. Theseinclude sharks, clams,crabs, clownfish,

eels, and manyother animals.

Corals are animals.They have a specialrelationship withalgae. Some algae need sunlight,so they only grow in shallow water.These algae grow inside the coral.Other algea help the coral make

a hard outside coating. Over time,many corals grow and die. Their hardoutside coatings pile up to make acoral reef. Many kinds of plants andanimals live in the reef.

Corals grow well in warm waterwith few nutrients and little oxygen.They are found near Florida,Australia, and many other places.

Coral reefs help to protect the shorefrom storms. They also provide uswith food and new types of medicine.

The Deep SeaSome very strange animals live in

deeper areas of the ocean. They mustdeal with cold, darkness, and veryhigh water pressure. These animalsare well-suited to the pressure. Some

will die if they come to the surface,where water pressure is lower.

Sunlight cannot reach these deepareas. So, no plants can grow. Manyanimals in the deep sea eat deadplants and animals that sink down.

Clams, crabs, and tubeworms livearound vents in the deep sea. Bacterialive there, too. They make food

from chemicals in the water. Thebacteria themselves are food forlarger animals.

Jellyfishbelong to thesame phylumas coral.

Tubeworms don’t havemouths or stomachs.Bacteria live inside thetubeworms and makefood that they share.

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How do organisms interact?Competition

Organisms often compete for things they need. They maycompete over space, food, or water. Sometimes they competefor their lives.

Animals of the same species compete. You may have heardcats screeching outside as they fight for territory. Animals ofdifferent species also compete. For example, rabbits and micein a desert community compete. They compete to find plantsfor food.

Plants may compete for sunlight or for water. The kudzuplant is very successful at competing for light. It covers otherplants, keeping them from getting any sunlight. Plants withlarger root systems will take in water faster than other plants.

SymbiosisSymbiosis is a long–term relationship between different

species. One of the species is always helped. The other might behelped, harmed, or not affected.

The buffalo and the cattle egret have one kind of symbiosis.As the buffalo moves through the grass, it scares up insects.

The egret can catch the insects easily. This helps the bird, but itdoesn’t affect the buffalo.

In another kind of symbiosis, very small organisms are fed asthey help the buffalo digest its food. Both species are helped.

The buffalo and worms show a third kind of symbiosis. Theworms live inside the buffalo. They get food, but the buffalomay become weak or sick. Organisms that feed on otherorganisms in this way are called parasites.

In a fourth kind of symbiosis, one organism can’t survive

without another. Lichen is a fungus and an algae livingtogether. The algae makes food from sunlight. The fungus couldnot survive without the food that the algae produces.

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Plants may compete forsunlight. Kudzu, shownhere, often covers otherplants in this competition.

The relationship betweenthe buffalo and the cattleegret is an example ofsymbiosis.



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How does energymove in ecosystems?Food Chains and Webs

All living things need energy to live. They get energy fromfood. The organism that is eaten gives food energy to theone that eats it. Producers are organisms such as plants,which make their own food. They get energy from sunlight orchemicals in nature. Consumers are organisms that cannotmake their own food. They must eat other organisms. Allanimals are consumers.

When food is eaten, the energy in the food moves from oneorganism to another. Food energy moves in chains such as this:

sun ➝

plants ➝

snowshoe hare ➝

spotted owl ➝

bacteriaThe diagram below shows many food chains combined in

one food web. You can see an ecosystem more fully in a webthan in a chain. That’s because consumers usually eat manykinds of other organisms.

Energy PyramidsAn energy pyramid is a diagram of a food chain. It shows

the flow of energy from one level to the next. The energypyramid is widest at the base. That’s because producers areshown at the base. They have the greatest amount of energy inan ecosystem.

Look higher on the energy pyramid. Notice that it getsnarrower as it rises. This shows that less energy flows throughhigher levels.

An energy pyramid has moreenergy at its base than atits top. This is because someenergy is given off as heat byeach organism in the pyramid.



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What cycles occurin ecosystems?Recycling Matter

Some substances go through an ecosystem again and again.They go in cycles. A cycle is a repeating flow of materialsthrough a system. There is a constant cycle of minerals andsome nutrients through ecosystems.

Decomposers play a key role in this cycle. Decomposers areorganisms that eat waste and dead matter. They break it intosmaller pieces and return it to the soil. In this way, decomposersrecycle waste and dead material. They make minerals andnutrients that were in their food available to living plants. Theplants will then be food for other organisms.

Nitrogen CyclePlants and animals need nitrogen to live. The air around us

is almost 810 nitrogen gas, but most living things cannot use this

form of nitrogen. Nitrogen is made into useable compoundsby lightning, and brought to the ground by rain. Compoundsare also made by bacteria. Plants take these compounds from

the soil.Some animals get nitrogen by eating plants. Others get it byeating plant eaters. Nitrogen returns to the soil when animalsdie and decay. It is also put into the soil in fertilizers used byfarmers. Plants use this nitrogen and the cycle begins again.

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Slugs, flies, and fungi aredecomposers. Whenever

you see something rotting,decomposers are at work.

Only a part of thenitrogen cycle isshown here.



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Carbon Dioxide and OxygenCarbon dioxide and oxygen gases are always being made

and used. Recall that plants take in carbon dioxide. They giveoff oxygen. Animals take in oxygen. They give off carbondioxide. Look at the diagram below. As it shows, oxygen andcarbon dioxide take many paths through an ecosystem.

Oxygen can enter the atmosphere during photosynthesis.Carbon dioxide can enter the atmosphere in many ways. Twomajor ways are respiration and combustion.

Respiration is a process that cells use to get energy. Theycombine oxygen with food. Plants and animals live byrespiration. The results are carbon dioxide and water.

Combustion is the burning of a material. It takes placenaturally, as in forest fires. It also happens in machines, suchas cars and furnaces.

Photosynthesis in plantsgives off oxygen. Volcanoes release

carbon dioxide.

Carbon dioxide isreleased when materialsare decomposed.

Combustion from cars,factories, and machinesgives off carbon dioxide.

Forest fires give offcarbon dioxide.

Plankton in the oceangive off oxygen.

Animals useoxygen and giveoff carbon dioxide.



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Glossary community the group of all the populations in

an area

cycle a repeating process or repeating flow ofmaterials through a system

ecosystem all the living and nonliving things inan area

energy pyramid a diagram that shows the flow of energythrough a food chain

habitat the place in an ecosystem in which anorganism lives

niche the job that an organism has in anecosystem

population a group of organisms of one species thatlive in an area at the same time

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What did you learn?1. What are some living and nonliving parts of an ecosystem?

2. In what group of ecosystems do rivers, wetlands, coral reefs,and the deep sea belong? What group is made up of forests,grasslands, deserts, and tundra?

3. Explain what a cycle in an ecosystem is. Give at leastone example.

4. Organisms have special behaviorsthat help them meet their needs. On your own paper, write toexplain how behaviors help organisms live in a biome whereit is very hot or very cold. Include details from the book tosupport your answer.

5. Predict Describe what might happen to a rainforestecosystem if its yearly rainfall decreased a great deal.

g5 lsr 1g 5.05 interactions in ecosystems

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