ecosystem changes life science

Scott Foresman Science 4.4
Genre Comprehension Skill Text Features Science Content
Nonfi ction Cause and Effect • Call Outs
• Captions
• Diagrams
• Glossary
Ecosystem
Changes
ISBN 0-328-13869-X
ì<(sk$m)=bdigjc< +^-Ä-U-Ä-U
13869_01-04_CVR_FSD.indd Cover113869_01-04_CVR_FSD.indd Cover1 5/12/05 6:44:16 PM5/12/05 6:44:16 PM
Scott Foresman Science 4.4
Genre Comprehension Skill Text Features Science Content
Nonfi ction Cause and Effect • Call Outs
• Captions
• Diagrams
• Glossary
Ecosystem
Changes
ISBN 0-328-13869-X
ì<(sk$m)=bdigjc< +^-Ä-U-Ä-U
13869_01-04_CVR_FSD.indd Cover113869_01-04_CVR_FSD.indd Cover1 5/12/05 6:44:16 PM5/12/05 6:44:16 PM
1. What can happen to an ecosystem if
one part of it is no longer balanced?
Give an example.
2. What do canines and felines in
Yellowstone National Park do to
decrease competition?
3. What can be done to prevent an
endangered species from becoming
extinct?

4.

The actions of people
can have dangerous effects on ecosystems.
Describe on your own paper what can be
done to help reverse harmful changes to
ecosystems. Include details from the book
to support your answer.
5.

Cause and Effect What are some
positive and negative effects of a fi re
in an ecosystem?
What did you learn?
Vocabulary
competition
endangered
extinct
hazardous wastes
host
parasite
succession
Picture Credits
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.
Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).
3 (TL) Digital Stock; 4 Digital Stock; 6 (R) Digital Vision; 7 (TL) Getty Images, (CL) Getty Images;
10 (T) Ron Austing; Frank Lane Picture Agency/Corbis, (R) Getty Images; 11 (BL) Getty Images; 13 (B) Getty Images;
14 (T) Getty Images; 16 Tom & Pat Leeson/Photo Researchers, Inc.; 19 Bettmann/Corbis; 20 Getty Images;
21 (C) Getty Images, (BL) Getty Images; 22 Getty Images; 23 Alamy Images.

Scott Foresman/Dorling Kindersley would also like to thank: 16 Natural History Museum, London/DK Images.
Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson.
ISBN: 0-328-13869-X
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 permission(s), 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
13869_01-04_CVR_FSD.indd Cover213869_01-04_CVR_FSD.indd Cover2 5/12/05 6:44:24 PM5/12/05 6:44:24 PM
by Donna Latham
13869_05-28_FSD.indd 113869_05-28_FSD.indd 1 5/12/05 6:45:56 PM5/12/05 6:45:56 PM
2
Balance
on the Trail
You are hiking in Yellowstone
National Park. It is the oldest
national park in the world. It is
also one of the biggest wildlife
preserves in the United States.
As you walk along the trail,
you can observe the balance of
nature. It’s all around you.
Look—over there. That adult
bull elk weighs close to one
thousand pounds. Its striking,
spreading antlers have twelve
points. As you quietly observe,
the elk grazes in the grasses
beneath the trail. The largest

herd of elk in the United States
can be found here. At one time,
elk could be found in the eastern
forests and prairies of the
United States. But they were
hunted so much that they died
out in many areas.
13869_05-28_FSD.indd 213869_05-28_FSD.indd 2 5/12/05 6:45:59 PM5/12/05 6:45:59 PM
3
Now look above
you. Do you see
that huge fl ock of
white pelicans? They soar
high over the trail until they fl y
out of sight. They are going on a
group fi shing expedition to one of
the park’s lakes. There they will
swim along the water’s surface.
Staying in a line, they will chase
the fi sh to shallow water. Once the
fi sh have been trapped there, the
pelicans will scoop them up
in their pouches and swallow
them whole.
That is how the balance of
nature works. Both the elk and
the white pelican survive in
Yellowstone National Park
because the environment gives
them everything they need to

live. All their needs are met in a
balanced ecosystem. Let’s fi nd
out how!
13869_05-28_FSD.indd 313869_05-28_FSD.indd 3 5/12/05 6:46:15 PM5/12/05 6:46:15 PM
4
Balanced Ecosystems
All living things depend on each other and their
environment to live and grow. The ways in which they
interact keep the ecosystem balanced.
What Living Things Need
Consider the elk you just saw along the hiking trail.
Every day it depends on the living and nonliving things
in the park to survive. Think about all the ways the
environment meets the elk’s needs. It gets food from
the grasses and trees that grow there. These plants give
oxygen, which the elk needs to breathe. Where do you
think the elk gets the water it drinks? Yellowstone’s rivers
and lakes, as well as streams and ponds, supply water. And
do not forget the puddles that rainwater supplies!
One of this elk’s needs is water.
13869_05-28_FSD.indd 413869_05-28_FSD.indd 4 5/12/05 6:46:25 PM5/12/05 6:46:25 PM
5
It’s summer now, so the elk lives in the higher
mountain areas. But in the winter, the elk and its herd
will move to the lower valley. They will stay there
together, where there is not much snow. Twigs from fi r
and juniper trees will provide food. By staying together
in a herd, the elk will be protected from predators such
as bears and wolves.
In order to grow and be healthy, all living things

need food, water, and living space. They must also
have shelter, light, and air. Organisms also need the
right soil and the right kind of weather conditions.
Living things survive in environments that meet all
of their needs.
Elk also need air and living space.
13869_05-28_FSD.indd 513869_05-28_FSD.indd 5 5/12/05 6:46:34 PM5/12/05 6:46:34 PM
6
Staying Balanced
To stay healthy, ecosystems must
be balanced. All living things in an
ecosystem are connected. If something
happens to just one thing, all the parts of
the ecosystem are affected. Suppose that
you have balanced a pyramid of oranges
on your desk. What would happen to
the pile if you removed one orange from
the middle? Everything would move and
shift. The whole pile might tumble down.
That is the way the balance of nature
works too.
In order for an ecosystem to be
balanced, the food supply, living space,
and shelter for a group of animals must
be just right. Let’s investigate the balance
of three living things in Yellowstone—the
weasel, the rabbit, and the clover plant.
13869_05-28_FSD.indd 613869_05-28_FSD.indd 6 5/12/05 6:46:42 PM5/12/05 6:46:42 PM
7
The clover, rabbit, and

weasel each play a role in the
balance of their ecosystem.
In order to live, clover needs
sunlight, water, and minerals
from the soil. It also needs
space. Rabbits need clover so
they can live and grow. By eating
clover, rabbits help keep it from
taking up space that other plants
need. By preying on rabbits,
the weasel makes sure that the
rabbit population does not get
too big. That way, the clover is
not completely eaten up. Other
plants and animals rely on the
clover for oxygen and moisture.
That keeps them all alive.
In a balanced ecosystem,
there is always change. First,
organisms are born. Then they
live and die. After death they
decompose. With these changes
constantly taking place, an
ecosystem can remain balanced.
13869_05-28_FSD.indd 713869_05-28_FSD.indd 7 5/12/05 6:47:04 PM5/12/05 6:47:04 PM
8
The Cycle of Change and Balance
Many changes cancel each other out. For example,
one rabbit may fall prey to a weasel, and elsewhere
another rabbit may be born. When water dries up from

a puddle, it is replaced during the next rainstorm. As
you can see below, animals take oxygen out of their
ecosystem when they breathe. But as new plants grow,
they put more oxygen back into the ecosystem.
And so it continues!
Animals use
up oxygen
when they
breathe.
THE OXYGEN
CYCLE
Oxygen is
replaced
in the air.
13869_05-28_FSD.indd 813869_05-28_FSD.indd 8 5/12/05 6:47:24 PM5/12/05 6:47:24 PM
9
When the number of resources
in an ecosystem changes, populations
change too. Think about the rabbit.
With plenty of clover and other plants
Organisms Interact
Changing Ecosystems
Within an ecosystem, organisms compete for
resources. But competition is just one way organisms
can interact.
to eat, it can live and grow. More
rabbits enter the ecosystem. But extra
rabbits require extra plants for food.
They need living space and water too.
In time, the rabbit population might

use up all these resources. The rabbits
will die or move away from the area.
When more rabbits move into a new
area, they will fi nd plenty of resources.
The cycle will begin again in a new
location. The rabbits will do well in
their new environment, because their
needs are met. Their population will
expand again. Eventually this new
location will not be able to meet their
needs. What might happen then?
Plants and
trees give
off oxygen.
13869_05-28_FSD.indd 913869_05-28_FSD.indd 9 5/12/05 6:47:32 PM5/12/05 6:47:32 PM
10
Competition
In an ecosystem,
organisms must compete
for and share resources.
Competition is the
struggle between two or
more species to use the
same limited resources.
Every organism has its
own adaptations that help
it compete for resources.
Successful adaptations help
organisms live and grow.
Living space is a survival

requirement. It is also a source
of competition. Different plant
species compete for water and
sunlight. Some plants grow
tall, for example, and choke
out others. Birds compete for
the same prime locations to
build their nests. Have you ever
seen a blue jay? This bird, with
its blaring call, actually takes
over other birds’ nests. During
nesting seasons, it tosses eggs
from other nests and moves in.
blue jay
13869_05-28_FSD.indd 1013869_05-28_FSD.indd 10 5/12/05 6:47:32 PM5/12/05 6:47:32 PM
11
Animals behave in
special ways to decrease
competition or to avoid it
completely. Consider the
canine and feline predators
of Yellowstone National
Park. Both groups prey on
small mammals, including
squirrels, rabbits, and
mice. These two groups of
predators have divided their
hunting turf. The canines
include wolves, coyotes,
and foxes. With their strong

bodies and quick running
abilities, they hunt in wide-
open areas. The feline
predators, including the
bobcat, cougar, and lynx,
hunt in woody areas. Since
their hunting style is based
on sneak attacks, they use
plants to help hide them
from their prey.
cougar
lynx
13869_05-28_FSD.indd 1113869_05-28_FSD.indd 11 5/12/05 6:47:47 PM5/12/05 6:47:47 PM
12
Living in Harmony
Organisms can live together and help each other.
The peony plant and some ants have a helpful
relationship. The peony has a waxy outer covering
on its bud. If this covering becomes too thick, it can
prevent the bud from opening. Ants get energy by
eating the coating off the bud. The ants need to eat the
coating, and the peony cannot bloom without the ants.
Parasites and Hosts
Not all the interactions in an ecosystem are helpful.
One organism may help itself while it harms another.
The organism that is helped is a parasite. The organism
that is often hurt is the host.
In Yellowstone, a microscopic parasite attacks the
cartilage in cutthroat trout. It becomes diffi cult for the
trout to feed, and they die. As the trout decompose,

they release spores of the parasite into the
water. Those spores fi nd new hosts.
13869_05-28_FSD.indd 1213869_05-28_FSD.indd 12 5/12/05 6:48:02 PM5/12/05 6:48:02 PM
13
Environments naturally
change. This can happen
very slowly or very quickly.
When an environment
changes, ecosystems and
their species can be affected.
A forest you might live
near or have visited may
have changed over time.
Thousands of years ago, it
may have been a lake. Over
time that lake dried up, and
a marsh took its place. As
more time passed, trees,
grass, and bushes replaced the
marsh, creating a forest.
Succession is the gradual
change from one community
of organisms to another. As
an environment changes,
Changing
Environments
succession takes place. In most cases, it takes place
in stages. Communities will grow and take over for
one another. Eventually, one community will become
another kind of community.

lake
forest
13869_05-28_FSD.indd 1313869_05-28_FSD.indd 13 5/12/05 6:48:11 PM5/12/05 6:48:11 PM
14
The Stages of
Succession
bare land
Succession takes place
over time. Climate changes,
such as warmer or colder
weather, can infl uence how
quickly succession occurs.
Bare land is often the
starting point. The land
provides weeds and some
herbs, which help the soil.
In time, grasslands grow.
Shrubs and grasses begin
to spread over the land.
Shrubs continue to
grow, making way for pine
trees. Over time, oak and
hickory trees begin to
replace the pine trees.
Finally, a mature forest
fully replaces the shrub land.
grassland
shrub land
forest
13869_05-28_FSD.indd 1413869_05-28_FSD.indd 14 5/12/05 6:48:16 PM5/12/05 6:48:16 PM

15
How Species Change
You know that dinosaurs are extinct. Did you
realize that many other animals are extinct too? When
an animal is extinct, the entire species has died out.
It is gone forever. Species become extinct for different
reasons. Climate changes, volcanoes, meteorites, and
human activities may have caused extinction.
The woolly mammoth is extinct. Its size was much
larger than that of a modern-day Asian elephant. It
was covered with a warm coat that protected it from
cold temperatures. Scientists believe that most woolly
mammoths died out about eleven
thousand years ago, partly
due to changes in their
environment.
The Steller’s sea cow is
another extinct animal.
Once there were nearly two
thousand of them in the
Bering Sea. But sailors hunted
them for food. The Steller’s
sea cow died out by 1768,
less than thirty years
after it was discovered.
13869_05-28_FSD.indd 1513869_05-28_FSD.indd 15 5/12/05 6:48:21 PM5/12/05 6:48:21 PM
16
Endangered Species
When the population of a species has become
very low, that species is endangered. An endangered

species is in danger of becoming extinct. Species that
might soon become endangered are called threatened
species. Sometimes endangered and threatened species
leave an environment. They try to fi nd a place where
they can survive.
The black-footed ferret of the western United
States is an endangered animal. Once there were many
of them. They eat prairie dogs and, similar to the
weasels they are related to, slip into burrows to
capture their prey. But ranchers thought the prairie
dogs were pests, and they began to kill them. With
their food supplies running low, the black-footed
ferrets began to die.
Scientists thought that all the black-footed ferrets
had died out. But when a group of them were discovered
in Wyoming, scientists
acted quickly. They
captured the population
and cared for the ferrets
in captivity. Since 1991,
captive-bred black-
footed ferrets have been
returned to the wild.
13869_05-28_FSD.indd 1613869_05-28_FSD.indd 16 5/12/05 6:48:30 PM5/12/05 6:48:30 PM
17
Species Past and Present
Have you ever seen a fossil? Fossils are
important clues to Earth’s past. They let us
know that life on Earth has not always been
the way it is now. Over long periods of time,

species have changed or adapted. Changes
in their environment caused them to do so.
Today, scientists compare fossils of organisms
to organisms that are alive today.
13869_05-28_FSD.indd 1713869_05-28_FSD.indd 17 5/12/05 6:48:49 PM5/12/05 6:48:49 PM
18
What do you know about sharks? You may know
that some species of shark have a huge set of jaws. This
allows them to capture and devour their prey. Now
think about this puzzle. Scientists discovered a bizarre
set of teeth from the Helicoprion, an ancient shark. It
lived 250 million years ago in waters off North America,
Japan, and Australia, among other places. What makes
the set of teeth bizarre is that they are in a spiral shape,
much like the shape of a circular saw. Scientists are still
working to fi gure out just how this set of buzz-saw teeth
fi t in the shark’s mouth.
13869_05-28_FSD.indd 1813869_05-28_FSD.indd 18 5/12/05 6:48:58 PM5/12/05 6:48:58 PM
19
Quick changes in a habitat can affect species
that live there. Think of extreme weather events.
A hurricane’s strong winds can rip up trees and tear
down plants. Heavy rains and huge waves can fl ood
a community. Lightning can strike a tree and start
a fi re that wipes out everything in its path. These
natural events can take resources away from the
species that need them.
But rapid events do not only cause harm. They
also play an important part in keeping an ecosystem
balanced. Fires clear away dead plant matter. They

make room for new plants to grow. Flooded areas
help fi sh populations grow.
Rapid Natural Changes
13869_05-28_FSD.indd 1913869_05-28_FSD.indd 19 5/12/05 6:49:04 PM5/12/05 6:49:04 PM
20
People and the
Environment
Like other organisms, people interact with their
environment. We get water, food, and shelter there.
But unlike other organisms, we can change the
environment to meet our needs. For example, we
clear land to build houses or roads. We cut down
trees. When we change the environment, we can
upset the balance of ecosystems.
The waste products we make disturb ecosystems
too. We pollute the air and water with these
products. With our cars and factories, we release
harmful chemicals into the air. Plants can die from
those chemicals. The animals that need those plants
might lose their food and shelter. When one action
takes place, it affects others.
13869_05-28_FSD.indd 2013869_05-28_FSD.indd 20 5/12/05 6:49:12 PM5/12/05 6:49:12 PM
21
When wastes and chemicals get into lakes, rivers,
and oceans, our water becomes polluted. Some
substances get into the water through sewer systems.
Some chemicals are useful for killing insects or helping
plants grow, but they can be harmful too. Rain washes
the chemicals from the land into our water. These
chemicals can kill fi sh and other animals and plants that

live in the water.
Water Pollution
Sometimes when oil is being
drilled or shipped, it is spilled.
The ocean’s plant and animal
inhabitants, such as this sea
bird, can be harmed.
13869_05-28_FSD.indd 2113869_05-28_FSD.indd 21 5/12/05 6:49:17 PM5/12/05 6:49:17 PM
22
Land Pollution
Garbage, litter, and other things pollute our land.
Did you know that in the United States every person
tosses out about two kilograms, or about four and one-
half pounds, of garbage each day? Most of that trash
is dumped into landfi lls and covered up with soil.
Land pollution also occurs in the disposal of
hazardous wastes. Hazardous wastes are substances
that can hurt humans and other organisms. They can
be poisonous or cause diseases. They can even start fi res.
At one time, hazardous wastes were placed into
barrels and buried. But some of the wastes leaked out.
They damaged the habitats where they were buried.
Today, laws require that hazardous waste disposal
follow strict rules.
13869_05-28_FSD.indd 2213869_05-28_FSD.indd 22 5/12/05 6:49:27 PM5/12/05 6:49:27 PM
23
Strip mining is a way of getting coal from under
Earth’s surface. Big machines dig up layers of soil to get
to the coal. This leaves behind huge holes. Rocks and
soil are swept into ponds and rivers, upsetting those

ecosystems. Now there are laws that require mining
companies to put back the rocks and soil that they
removed. This is called reclamation. It helps restore
habitats.
You have learned that living things depend on
one another and on their environments. You know
that changes in an environment will affect all living
things that inhabit it. It is true of the environment in
Yellowstone National Park. And it is true of your
own environment as well!
Strip Mining
13869_05-28_FSD.indd 2313869_05-28_FSD.indd 23 5/12/05 6:49:39 PM5/12/05 6:49:39 PM
24
Glossary
competition the struggle between organisms to meet
their needs or to use the same resources
endangered a species that is at risk of dying out
extinct a species that has totally died out
hazardous materials that are harmful to
wastes people and other organisms, as well as
to the environment
host an organism that provides food or shelter
to another living thing
parasite an organism that lives on or in another
living thing and often harms it
succession the process of one community taking
the place of another over time
13869_05-28_FSD.indd 2413869_05-28_FSD.indd 24 5/12/05 6:49:46 PM5/12/05 6:49:46 PM
1. What can happen to an ecosystem if
one part of it is no longer balanced?

Give an example.
2. What do canines and felines in
Yellowstone National Park do to
decrease competition?
3. What can be done to prevent an
endangered species from becoming
extinct?
4.

The actions of people
can have dangerous effects on ecosystems.
Describe on your own paper what can be
done to help reverse harmful changes to
ecosystems. Include details from the book
to support your answer.
5.

Cause and Effect What are some
positive and negative effects of a fi re
in an ecosystem?
What did you learn?
Vocabulary
competition
endangered
extinct
hazardous wastes
host
parasite
succession
Picture Credits

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.
Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).
3 (TL) Digital Stock; 4 Digital Stock; 6 (R) Digital Vision; 7 (TL) Getty Images, (CL) Getty Images;
10 (T) Ron Austing; Frank Lane Picture Agency/Corbis, (R) Getty Images; 11 (BL) Getty Images; 13 (B) Getty Images;
14 (T) Getty Images; 16 Tom & Pat Leeson/Photo Researchers, Inc.; 19 Bettmann/Corbis; 20 Getty Images;
21 (C) Getty Images, (BL) Getty Images; 22 Getty Images; 23 Alamy Images.
Scott Foresman/Dorling Kindersley would also like to thank: 16 Natural History Museum, London/DK Images.
Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson.
ISBN: 0-328-13869-X
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 permission(s), 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
13869_01-04_CVR_FSD.indd Cover213869_01-04_CVR_FSD.indd Cover2 5/12/05 6:44:24 PM5/12/05 6:44:24 PM