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by Patricia Fitzhugh
Scott Foresman Science 5.5
Genre Comprehension Skill Text Features Science Content
Nonfi ction Predict • Labels
• Captions
• Diagrams
• Glossary
Interactions in Ecosystems
ISBN 0-328-13928-9
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Illustration Title Page, 20, 21, 22 Adam Benton Photographs:
Every effort has been made to secure permission and provide
appropriate credit for photographic material. The publisher deeply
regrets any omission and pledges to correct errors called to its
attention in subsequent editions. Unless otherwise acknowledged,
all photographs are the property of Scott Foresman, a division of
Pearson Education. Photo locators denoted as follows: Top (T),
Center (C), Bottom (B), Left (L), Right (R) Background (Bkgd)
Opener: ©Claus Meyer/Minden Pictures 2 (CC) ©D. Robert & Lorri
Franz/Corbis, (Bkgd) ©Larry Michael/Nature Picture Library, (BL)
©Joe McDonald/Animals Animals/Earth Scenes 5 ©Galen Rowell/Corbis 6
(CL) ©DK Images, (R) ©Michael Fogden/OSF/Animals Animals/Earth
Scenes 7 (BR) ©Tom Brakefield /Corbis, (L) ©Carr Clifton/Minden
Pictures 8 (BL) ©W. Perry Conway/Corbis, (R) ©Phil
Schermeister/Corbis 9 (L) ©W. Wayne Lockwood, M.D./Corbis, (BR)
©Ron Sanford/Corbis 10 (R) ©Diego Lezama Orezzoli/Corbis, (BR)
Jerry Young/©DK Images 11 (BL) ©Ron Sanford/Corbis, (BL) ©Roy
Corral/Corbis 12 (R) ©David Muench/Corbis, (BC) ©Jim
Zuckerman/Corbis 13 (L) ©David Muench/Corbis, (BC) ©Frank
Greenaway/©DK Images 14 (TC) ©Frank Greenaway/©DK Images, (BL)
©Stuart Westmorland/Corbis, (R) ©Stephen Frink/Corbis 15 (L, BR)
©Ralph White/Corbis 16 ©Bill Kamin/Visuals Unlimited 17 ©Stephen
Frink/Corbis 18 (BL) ©Michael Sewell/Peter Arnold, Inc., (BL) ©DK
Images, (BC) ©Daniel Cox/Getty Images, (BC) ©Michael Quinton/Minden
Pictures, (BC) ©John Shaw/Tom Stack & Associates, Inc., (BC,
BL) Neil Fletcher and Matthew Ward/©DK Images, (BR) Getty Images,
(BL) Matthew Ward/©DK Images 19 (CL) ©Michael Sewell/Peter Arnold,
Inc., (CL) ©Michael Quinton/Minden Pictures, (BL, BC) Neil Fletcher
and Matthew Ward/©DK Images
ISBN: 0-328-13928-9
Copyright © Pearson Education, Inc.
All Rights Reserved. Printed in the United States of America.
This publication is protected by Copyright and permission should be
obtained from the publisher prior to any prohibited reproduction,
storage in a retrieval system, or transmission in any form by any
means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permissions, write to:
Permissions Department, Scott Foresman, 1900 East Lake Avenue,
Glenview, Illinois 60025.
3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05
Vocabularycommunity
cycle
ecosystem
energy pyramid
habitat
niche
population
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 least one
example.
4. Organisms have special behaviors that help them meet their
needs. On your own paper, write to explain how behaviors help
organisms live in a biome where it is very hot or very cold.
Include details from the book to support your answer.
5. Predict Describe what might happen to a rainforest ecosystem
if its yearly rainfall decreased a great deal.
13928_CVR_FSD Sec1:213928_CVR_FSD Sec1:2 5/27/05 10:33:29
AM5/27/05 10:33:29 AM
Interactions in Ecosystemsby Patricia Fitzhugh
13928_01-24_FSD 113928_01-24_FSD 1 5/27/05 11:24:10 AM5/27/05
11:24:10 AM
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A community is a bigger part of an ecosystem. A community is all
the populations in an area. Members of a community 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 what kinds of
organisms—and how many—can live in an ecosystem.
If a population’s needs are not met in an ecosystem, that
population 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. An
ecosystem 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 an area at
the same time. This may be all the oak trees. It may be all 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. The climate and
organisms are generally the same in all parts of the biome.
There are several kinds of biomes. One kind is a rainforest. A
rainforest biome has large amounts of rain and thick plant
growth.
The United States has a rainforest biome in the state of
Washington. This rainforest is a temperate rainforest. It receives
a lot of rain, but can be quite cool.
Each living thing in an ecosystem has a niche. A niche is an
organism’s role in an ecosystem. For example, the spotted owl has a
niche in the temperate rainforest. It is a hunter. The owl hunts
and eats small animals, such as mice.
Each living thing also has a habitat. A habitat is where an
organism lives. The spotted owl’s habitats are the trees and land
where it lives.
All the relationships in an ecosystem keep it balanced. For
example, the populations of mice and spotted owls balance each
other. It works like this:
If the number of mice drops, the owls will have less food. So,
the number of owls will drop, too. With fewer owls hunting, fewer
mice will be eaten. So, the population of mice will grow. Then owls
will have more mice to hunt. So, the population of owls will grow
again.
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What are land biomes?Tropical Rainforest Biomes
Ecosystems near the equator are always warm. Some of them get a
lot of rain—more than three meters each year. In these places plant
populations grow large. A tropical rainforest results.
Tropical rainforests have more different kinds of life than any
other biome. There may be dozens of different species living in a
single tree.
Deciduous Forest BiomesDeciduous forests grow in cooler
areas. They cover much of the eastern United States. Oak, elm,
and maple trees grow in these biomes. These are deciduous trees.
That means that they lose their leaves when it gets cold. This
helps them save food and water.
Some other organisms also change in colder seasons. Bears sleep
through much of the winter. Snakes and frogs stay underground. Some
rabbits’ fur becomes snowy white. This helps the rabbits blend in
with the snow. They can easily hide from animals that hunt
them.
Organisms have structures that help them survive. The kinkajou’s
long tongue can get honey and insects. Its tail can grab onto
branches.
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Grassland BiomesGrasslands are biomes with many
types of grasses. Grasslands do not get much rain. So few trees
can grow in these biomes.
Grasslands once covered huge areas of the midwestern United
States. Then settlers came. Over many years, settlers turned most
of the grasslands into farms.
Bison, antelope, and prairie dogs live on the grasslands. The
changing of this habitat into farms has affected animal
populations. For example, gray wolves once hunted prairie dogs.
Farming reduced the prairie dog population, so the wolves had less
to eat. People also hunted the wolves. These changes caused the
gray wolf population to fall very low.
Taiga BiomesA taiga is a kind of forest biome.
Tiagas are found in areas that are cold and fairly dry. They
cover much of 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 all year long so they are ready to make food
as soon as warm weather arrives. They have a waxy coating that
helps the tree hold water.
Large animals such as bear, elk, and moose live in the taiga.
Smaller animals such as porcupines and mice live there as well. All
these animals have fur. It keeps them warm. Ducks, owls, and
woodpeckers also live in the taiga. These animals have feathers to
help keep them warm.
Gray wolves once lived over most of North America. Now wolves
live in only a small part of this area.
The moose is a very large animal found in the taiga.
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10 11
Desert BiomesDeserts are areas that get less than
25 cm of rain or snow each year. All deserts have low rainfall.
Many deserts are very hot, but others are cold most of the time.
Some deserts have sand dunes and others are very rocky. Large
deserts are found in Africa, Asia, and Australia.
Desert animals may include rattlesnakes, lizards, jackrabbits,
and beetles. Plants may include bushes, grasses, and cactuses.
Desert plants have special parts that help them live without
much water. Some have large root systems close to the surface of
Earth. These roots can take in rainwater quickly.
Desert animals have special behaviors that help them survive.
Many animals rest during the hot 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 far northern parts of the
world. Rodents, rabbits, and caribou live on the tundra. Tundra
animals may also include weasels, owls, and foxes.
In any ecosystem, a population can only grow so large. The
number of organisms that can live in a place is the carrying
capacity. If a population grows larger than the carrying capacity,
there won’t be enough food, water, space, or shelter.
Populations will have to move to another area to survive.
On the tundra, cold weather makes it hard for plants to grow.
The small plants that do grow cannot provide enough food and
shetler for animals. This keeps the carrying capacity low.
Emus are found in many areas of Australia, including
deserts.
When snow covers the tundra, caribou often move to warmer areas
to find food.
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What are water ecosystems?Rivers
Many different animals live in rivers. They include fish, ducks,
turtles, and insects. Some animals live only in rivers that flow
slowly.
River ecosystems also include animals that spend much of their
time on land. The river otter, for example, does well in both
environments. In the water, its sleek body lets it swim fast to
catch fish. While swimming, it can close its nose and ears. On
land, it can run to catch frogs and small mammals.
Organisms that live in rivers usually do not also live in
oceans. The ocean water is too salty for their cells.
WetlandsThere are many kinds of wetlands.
All are partly covered with water or flooded at least part of
each year. Florida’s Everglades is a wetland. It has huge areas of
sawgrass that grows more than 3 meters tall. Alligators, fish,
deer, and snakes live in the Everglades.
A swamp is a wetland with many trees and bushes. Deer, otters,
turtles, snakes, and wild pigs may live in swamps.
Some wetlands are parts of estuaries. These are places where
rivers flow into the ocean. Grassy wetlands called salt marshes are
found in estuaries.
Wetlands are helpful in many ways. The plants, soils, and tiny
organisms of wetlands often act as filters. They clean water that
flows through the wetland.
The river otter can live easily on the land or in the water.
Crayfish are often found in swamp ecosystems.
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Coral ReefsCoral reefs are
home to many types of organisms. These include sharks, clams,
crabs, clownfish, eels, and many other animals.
Corals are animals. They have a special relationship with algae.
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 hard
outside coatings pile up to make a coral reef. Many kinds of plants
and animals live in the reef.
Corals grow well in warm water with few nutrients and little
oxygen. They are found near Florida, Australia, and many other
places. Coral reefs help to protect the shore from storms. They
also provide us with food and new types of medicine.
The Deep SeaSome very strange animals live in
deeper areas of the ocean. They must deal with cold, darkness,
and very high water pressure. These animals are well-suited to the
pressure. Some will die if they come to the surface, where water
pressure is lower.
Sunlight cannot reach these deep areas. So, no plants can grow.
Many animals in the deep sea eat dead plants and animals that sink
down.
Clams, crabs, and tubeworms live around vents in the deep sea.
Bacteria live there, too. They make food from chemicals in the
water. The bacteria themselves are food for larger animals.
Jellyfish belong to the same phylum as coral.
Tubeworms don’t have mouths or stomachs. Bacteria live inside
the tubeworms and make food that they share.
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How do organisms interact?Competition
Organisms often compete for things they need. They may compete
over space, food, or water. Sometimes they compete for their
lives.
Animals of the same species compete. You may have heard cats
screeching outside as they fight for territory. Animals of
different species also compete. For example, rabbits and mice in a
desert community compete. They compete to find plants for food.
Plants may compete for sunlight or for water. The kudzu plant is
very successful at competing for light. It covers other plants,
keeping them from getting any sunlight. Plants with larger 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 be
helped, 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 it
doesn’t affect the buffalo.
In another kind of symbiosis, very small organisms are fed as
they help the buffalo digest its food. Both species are helped.
The buffalo and worms show a third kind of symbiosis. The worms
live inside the buffalo. They get food, but the buffalo may become
weak or sick. Organisms that feed on other organisms 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 living together.
The algae makes food from sunlight. The fungus could not survive
without the food that the algae produces.
16 17
Plants may compete for sunlight. Kudzu, shown here, often covers
other plants in this competition.
The relationship between the buffalo and the cattle egret is an
example of symbiosis.
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18 19
How does energy move in ecosystems?Food Chains and Webs
All living things need energy to live. They get energy from
food. The organism that is eaten gives food energy to the one that
eats it. Producers are organisms such as plants, which make their
own food. They get energy from sunlight or chemicals in nature.
Consumers are organisms that cannot make their own food. They must
eat other organisms. All animals are consumers.
When food is eaten, the energy in the food moves from one
organism to another. Food energy moves in chains such as this:
sun ➝ plants ➝ snowshoe hare ➝ spotted owl ➝ bacteria
The diagram below shows many food chains combined in one food
web. You can see an ecosystem more fully in a web than in a chain.
That’s because consumers usually eat many kinds 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 energy
pyramid is widest at the base. That’s because producers are shown
at the base. They have the greatest amount of energy in an
ecosystem.
Look higher on the energy pyramid. Notice that it gets narrower
as it rises. This shows that less energy flows through higher
levels.
An energy pyramid has more energy at its base than at its top.
This is because some energy is given off as heat by each organism
in the pyramid.
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What cycles occur in ecosystems?Recycling Matter
Some substances go through an ecosystem again and again. They go
in cycles. A cycle is a repeating flow of materials through a
system. There is a constant cycle of minerals and some nutrients
through ecosystems.
Decomposers play a key role in this cycle. Decomposers are
organisms that eat waste and dead matter. They break it into
smaller pieces and return it to the soil. In this way, decomposers
recycle waste and dead material. They make minerals and nutrients
that were in their food available to living plants. The plants 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 compounds by
lightning, and brought to the ground by rain. Compounds are also
made by bacteria. Plants take these compounds from the soil.
Some animals get nitrogen by eating plants. Others get it by
eating plant eaters. Nitrogen returns to the soil when animals die
and decay. It is also put into the soil in fertilizers used by
farmers. Plants use this nitrogen and the cycle begins again.
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Slugs, flies, and fungi are decomposers. Whenever you see
something rotting, decomposers are at work.
Only a part of the nitrogen cycle is shown here.
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22 23
Carbon Dioxide and OxygenCarbon dioxide and oxygen gases are
always being made
and used. Recall that plants take in carbon dioxide. They give
off oxygen. Animals take in oxygen. They give off carbon dioxide.
Look at the diagram below. As it shows, oxygen and carbon dioxide
take many paths through an ecosystem.
Oxygen can enter the atmosphere during photosynthesis. Carbon
dioxide can enter the atmosphere in many ways. Two major ways are
respiration and combustion.
Respiration is a process that cells use to get energy. They
combine oxygen with food. Plants and animals live by respiration.
The results are carbon dioxide and water.
Combustion is the burning of a material. It takes place
naturally, as in forest fires. It also happens in machines, such as
cars and furnaces.
Photosynthesis in plants gives off oxygen. Volcanoes release
carbon dioxide.
Carbon dioxide is released when materials are decomposed.
Combustion from cars, factories, and machines gives off carbon
dioxide.
Forest fires give off carbon dioxide.
Plankton in the ocean give off oxygen.
Animals use oxygen and give off carbon dioxide.
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Glossarycommunity the group of all the populations in
an area
cycle a repeating process or repeating flow of materials through
a system
ecosystem all the living and nonliving things in an area
energy pyramid a diagram that shows the flow of energy through a
food chain
habitat the place in an ecosystem in which an organism lives
niche the job that an organism has in an ecosystem
population a group of organisms of one species that live in an
area at the same time
13928_01-24_FSD 2413928_01-24_FSD 24 5/27/05 11:28:01 AM5/27/05
11:28:01 AM
Illustration Title Page, 20, 21, 22 Adam Benton Photographs:
Every effort has been made to secure permission and provide
appropriate credit for photographic material. The publisher deeply
regrets any omission and pledges to correct errors called to its
attention in subsequent editions. Unless otherwise acknowledged,
all photographs are the property of Scott Foresman, a division of
Pearson Education. Photo locators denoted as follows: Top (T),
Center (C), Bottom (B), Left (L), Right (R) Background (Bkgd)
Opener: ©Claus Meyer/Minden Pictures 2 (CC) ©D. Robert & Lorri
Franz/Corbis, (Bkgd) ©Larry Michael/Nature Picture Library, (BL)
©Joe McDonald/Animals Animals/Earth Scenes 5 ©Galen Rowell/Corbis 6
(CL) ©DK Images, (R) ©Michael Fogden/OSF/Animals Animals/Earth
Scenes 7 (BR) ©Tom Brakefield /Corbis, (L) ©Carr Clifton/Minden
Pictures 8 (BL) ©W. Perry Conway/Corbis, (R) ©Phil
Schermeister/Corbis 9 (L) ©W. Wayne Lockwood, M.D./Corbis, (BR)
©Ron Sanford/Corbis 10 (R) ©Diego Lezama Orezzoli/Corbis, (BR)
Jerry Young/©DK Images 11 (BL) ©Ron Sanford/Corbis, (BL) ©Roy
Corral/Corbis 12 (R) ©David Muench/Corbis, (BC) ©Jim
Zuckerman/Corbis 13 (L) ©David Muench/Corbis, (BC) ©Frank
Greenaway/©DK Images 14 (TC) ©Frank Greenaway/©DK Images, (BL)
©Stuart Westmorland/Corbis, (R) ©Stephen Frink/Corbis 15 (L, BR)
©Ralph White/Corbis 16 ©Bill Kamin/Visuals Unlimited 17 ©Stephen
Frink/Corbis 18 (BL) ©Michael Sewell/Peter Arnold, Inc., (BL) ©DK
Images, (BC) ©Daniel Cox/Getty Images, (BC) ©Michael Quinton/Minden
Pictures, (BC) ©John Shaw/Tom Stack & Associates, Inc., (BC,
BL) Neil Fletcher and Matthew Ward/©DK Images, (BR) Getty Images,
(BL) Matthew Ward/©DK Images 19 (CL) ©Michael Sewell/Peter Arnold,
Inc., (CL) ©Michael Quinton/Minden Pictures, (BL, BC) Neil Fletcher
and Matthew Ward/©DK Images
ISBN: 0-328-13928-9
Copyright © Pearson Education, Inc.
All Rights Reserved. Printed in the United States of America.
This publication is protected by Copyright and permission should be
obtained from the publisher prior to any prohibited reproduction,
storage in a retrieval system, or transmission in any form by any
means, electronic, mechanical, photocopying, recording, or
likewise. For information regarding permissions, write to:
Permissions Department, Scott Foresman, 1900 East Lake Avenue,
Glenview, Illinois 60025.
3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05
Vocabularycommunity
cycle
ecosystem
energy pyramid
habitat
niche
population
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 least one
example.
4. Organisms have special behaviors that help them meet their
needs. On your own paper, write to explain how behaviors help
organisms live in a biome where it is very hot or very cold.
Include details from the book to support your answer.
5. Predict Describe what might happen to a rainforest ecosystem
if its yearly rainfall decreased a great deal.
13928_CVR_FSD Sec1:213928_CVR_FSD Sec1:2 5/27/05 10:33:29
AM5/27/05 10:33:29 AM
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