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Interactions
in Ecosystems
Scott Foresman Science 5.5
ISBN 0-328-13928-9
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by Patricia Fitzhugh
Vocabulary
What did you learn?
community
1. What are some living and nonliving parts of an ecosystem?
cycle
PatriciadoFitzhugh
2. In what group by
of ecosystems
rivers, wetlands, coral reefs,
and the deep sea belong? What group is made up of forests,
grasslands, deserts, and tundra?
ecosystem
energy pyramid
habitat
niche
population
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
Interactions in Ecosystems
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.
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.
2
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.
3
Biomes
A 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.
4
5
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 Biomes
Deciduous 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.
6
7
Grassland Biomes
Taiga Biomes
Grasslands 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.
A 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.
The moose is a
very large animal
found in the taiga.
Gray wolves once lived
over most of North
America. Now wolves
live in only a small part
of this area.
8
9
Desert Biomes
Tundra Biomes
Deserts 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.
The 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.
10
11
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.
The river otter can live
easily on the land or
in the water.
12
Wetlands
There 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.
Crayfish are
often found
in swamp
ecosystems.
13
Coral Reefs
The Deep Sea
Coral reefs are
home to many types
of organisms. These
include sharks, clams,
crabs, clownfish,
eels, and many
Jellyfish
other animals.
belong to the
Corals are animals.
same phylum
They have a special
as coral.
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.
Some 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.
14
Tubeworms don’t have
mouths or stomachs.
Bacteria live inside the
tubeworms and make
food that they share.
15
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.
Symbiosis
Symbiosis 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.
The relationship between
the buffalo and the cattle
egret is an example of
symbiosis.
Plants may compete for
sunlight. Kudzu, shown
here, often covers other
plants in this competition.
16
17
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:
Energy Pyramids
An 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.
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.
18
19
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 Cycle
Plants and animals need nitrogen to live. The air around us
8
is almost 10 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.
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.
20
21
Carbon Dioxide and Oxygen
Carbon 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.
Animals use
oxygen and give
off carbon dioxide.
Photosynthesis in plants
gives off oxygen.
Volcanoes release
carbon dioxide.
Forest fires give off
carbon dioxide.
Carbon dioxide is
released when materials
are decomposed.
Combustion from cars,
factories, and machines
gives off carbon dioxide.
Plankton in the ocean
give off oxygen.
22
23
Vocabulary
Glossary
community
community
cycle
cycle
ecosystem
energy
pyramid
ecosystem
habitat
energy
niche pyramid
population
What did you learn?
the group of all the populations in
an area
a repeating process or repeating flow of
materials through a system
all the living and nonliving things in
an area
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
Illustration Title Page, 20, 21, 22 Adam Benton
Photographs: Every effort has been
made
secure
permission
and provide
live
intoan
area
at the
sameappropriate
time 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
24
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.