Genre Comprehension Skill Text Features Science Content

Nonfi ction Make Inferences Captions

Glossary

Changing Environments

Scott Foresman Science 3.5

StandardsPreview

Standard Set 3. Life Sciences

3. Adaptations in physical structure or behavior may improve an organisms chance for survival. As a basis for understanding this concept:

3.c. Students know living things cause changes in the environment in which they live: some of these changes are detrimental to the organism or other organisms, and some are beneficial.

3.d. Students know when the environment changes, some plants and animals survive and reproduce; others die or move to new locations.

3.e. Students know that some kinds of organisms that once lived on Earth have completely disappeared and that some of those resembled others that are alive today.

ISBN 0-328-23531-8

Vocabulary

competitionextinctfossilhabitat

Picture CreditsEvery 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 copyright of Dorling Kindersley, a division of Pearson.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

Opener: U.S. Geological Survey, Corbis, AP/Wide World Photos, Visuals Unlimited; 1 (C) Douglas Faulkner/Corbis; 2 (B) Corbis; 4 (C) Animals Animals/Earth Scenes; 6 (B) AP/Wide World Photos; 7 (T) Animals Animals/Earth Scenes; 8 (B) Jeff Foott/Nature Picture Library; 10 (C) U.S. Geological Survey; 11 (BR) AP/Wide World Photos; 12 (C) Corbis; 13 (B) Douglas Faulkner/Corbis; 14 (C) Corbis; 15 (C) The Image Works, Inc.; 16 (B) Visuals Unlimited, (C) James L. Amos/Photo Researchers, Inc.; 17 (B) Visuals Unlimited, (C) Photo Researchers, Inc.; 18 (C) Getty Images; 19 (C) Photo Researchers, Inc.

ISBN: 0-328-23531-8

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 anyprohibited 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 toPermissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025.

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by Kim Fields

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2Living Things Change The Environment

A habitat is a place where a living thing makes its home. A habitat provides the resources a living thing needs to survive and grow.

Think of a habitat as a balance. One side of a habitat has the resources a habitat supplies. The other side has the things that live there. If the habitat has enough resources to help support life, the balance is level.

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Change often shifts the balance. When two or more living things need the same things, they are in competition. The gray seal and the harbor seal live in Canada. If there are too many seals or too little food, the same kind of seals are in competition. Some seals may die.

Too many seals or too little food leads to competition.

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4Changes Caused by Animals Some animals change their habitats when they make

homes. Beavers, for instance, need deep water. If the stream where they live is too shallow, they build a pond.Beavers use their sharp teeth to cut down trees. Beavers then put together dams from these trees. A dam creates a pond.

TK

Beavers change the environment when they build dams.

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This change helps plants and animals that need still water. Dragonfl ies can live in this new environment. Also, the trees the beavers cut down no longer shade the ground below. Small plants and shrubs that benefi t from direct sunlight grow in their place.

The change harms plants and animals that live in the moving waters of a river or stream. Some plants and animals no longer have a place to live. This change can affect fi sh. The pond harms plants and animals whose homes are fl ooded. Trees needed to make the dam are also lost.

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6Changes Caused by PeopleAll living things need shelter to stay alive. People need

shelter just like other living things. Humans change the environment when they build homes. To make room for houses, people may plow grasslands. They may cut down trees. Each of these changes affects the environment.

Sometimes animals and humans are in competition for space. People move to places where animals live. Then they might see coyotes in their backyards!

TK

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Helpful and Harmful ChangeChanges can help some living things and hurt others.

Kudzu is a plant brought to the United States that many people use to decorate their yards. It can help keep the soil from washing away.

Kudzu also causes many problems. It is hard to get rid of. No animals eat the plant. Kudzu grows fast and thick. It stops a forest from getting the light it needs to grow. Kudzu breaks other plants with its weight.

Cycles of ChangeSome changes happen in a cycle. Scientists believe a

change in the weather affects small fi sh called sardines. The overall weather around Monterey Bay changes in a fi fty-year cycle. In the 1930s, there were many sardines in the bay. By the 1950s, most of the sardines disappeared. By 1999, there were many sardines in the bay again.

This picture shows kudzu invading the living space of other plants. No animals eat kudzu. Nothing stops it from growing more. It covers other plants and gets all the sunlight.

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8Changes in The Environment Affect Living ThingsToo Little Water

Humans can change environments by taking too much water from streams and lakes. Plants and animals that need the water can die.

Dry weather can also change environments. It may be too dry for plants to survive and reproduce. Animals die or move somewhere else.

A dry season in Imperial Valley, California

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Over thousands of years, many places have become drier. In these places, grasses and shrubs that need less water have replaced trees that need a lot of water. Animals that use trees for food and homes are replaced by animals that use grasses and shrubs for food and homes.

Too Much WaterToo much water at the same time can change an

environment. Storms can cause fl ooding. Floods can wash away peoples homes. Floods can also wash away plants and soil. Animals, including snakes, can lose their homes to fl ooding. Floods carry thick blankets of mud to different places.

Flooding in Linda, California

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Volcanic EruptionIn the spring of 1980, a huge volcano erupted in

Washington State. Hot rock and gases from Mt. St. Helens melted ice and snow. The water caused a fl ood. One side of the mountain broke apart and slid away. The volcano blew a cloud of ash into the air. Even though it was daytime, the sky grew dark. Wind carried the ash all over the world.

The eruption changed the environment. Many forests were destroyed. Mud covered whole areas. Ash was piled up a meter high in some places.

In 1980, Mt. St. Helens erupted.

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After the EruptionSome shrubs and plant roots covered by snow

survived the eruption. Seeds carried by the wind sprouted and grew. As plants grew, more animals could fi nd food.

Animals that lived underground also lived through the eruption. Gophers, mice, spiders, and ants were safe from the eruption. Voles, shrews, and mice came to live on the mountain. Birds came to live in the dead trees that were left. Large elk, hawks, and eagles also came to live on the mountain.

The environment wont be like it was for a long time. But there are many living things on the mountain. Each new change on the mountain allows different types of animals and plants to live there.

Elk came to live on the mountain as plants grew back.

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Wildfi reA wildfi re brings a huge change to a forest. When

lightning strikes a tree in the forest, it can set the forest on fi re. Then the fi re rushes through the forest. Small plants and dead brush burn. Trees with thick bark live through the wildfi re. Other trees may burn down. This creates open spaces in the forest.

The temperature of a wildfi re can reach 800C.

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After a FireAnimals that hunt go back into the burnt forest. The

animals they hunt do not have many places to hide. Animals and wind carry in new seeds to the forest. Shrubs, fl owers, and grasses that can live with a lot of sunlight grow. The changes these plants bring help the next group of plants. Then new trees can grow in the forest. After a while, the forest grows back.

Fire causes harmful and helpful changes. Fire destroys animals homes. Many living things die. Wildfi res are also helpful for many plants and animals. They clear out the forest fl oor. New trees and plants have more space to live. The ash makes the soil healthy, helping plants to grow.

Young trees grow with plenty of living space and sunlight.

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Comparing Living Things to Those Of Long AgoFossils

An environment can change. Some kinds of animals and plants may not adapt to this change. The change may cause some animals and plants to become extinct. Extinct means no longer living on Earth.

During Earths history, many plants and animals have become extinct. We cannot see these plants and animals because they no longer live on Earth. We can, however, study the fossils left by extinct plants and animals. A fossil is the remains or mark of a living thing from long ago.

This is a fossil of a giant wombats jawbone.

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What Fossils Tell UsFossils tell us things about extinct animals and plants

and where they lived. We can tell how extinct animals and plants are like those alive today. We can also tell how they are different. The fossil of a giant wombat, for instance, was found in Australia. It was the size of a small car! It lived at a time when many giant creatures were on Earth.

We can also fi nd out how the environments of these plants and animals changed. Fossils of animals with teeth for eating plants might be found in a desert. This shows that the area may have once been a swamp.

An Australian wombat

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Plants Change over TimeThe fi rst plants did not have cones or fl owers.

Actually, many of them looked like the ferns and horsetails we have today. We can tell this by looking at plant fossils. Horsetails live in moist environments and can be found across the United States.

As Earth changed over time, many plants also changed. Trees with cones appeared. Then plants that had fl owers followed. Many of these kinds of plants no longer exist.

Horsetail fossil

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Like horsetails, magnolias are a kind of plant that still exists today. The fi rst magnolias kept their leaves year-round. They lived in a warm, wet world.

Some magnolias changed as environments changed. Many places where magnolias live have cold winters. Magnolias that live there lose their leaves in fall. Still, the fl owers and leaves of the magnolias are like those that lived a long time ago. The fl ower of the magnolia has stayed nearly the same for 100 million years.

Magnolia leaf fossil

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Animals Change over TimeFossils of extinct dinosaurs show how those dinosaurs

are like animals of today. Animals have teeth that are adapted to eat certain types of food. Animals that eat plants have grinding teeth. Animals that eat meat have teeth that tear and cut. You can look at the teeth of extinct animals to fi nd out what they ate.

Scientists in England assembled an 84-foot-long dinosaur skeleton.

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Some dinosaurs used their sharp teeth to tear off meat from other animals. Velociraptors were small dinosaurs, but they had sharp teeth! Velociraptors could attack and eat larger animals.

Other dinosaurs had teeth that could grind up food. Diplodocus had small teeth for grinding up plants.

Fossils can show us how Earth has changed over time. When scientists fi nd fossils of animals that ate plants, they know that the area had many plants. But today the same area may not have very many plants!

Velociraptor skull

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competition when two or more living things need the same resources

extinct no longer lives on Earth

fossil the remains or mark of a living thing from long ago

habitat the place where a living thing makes its home

Glossary

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What did you learn?1. How can beavers harm the environment when they

build dams?

2. How can dry weather affect animals?

3. How did some plants survive the eruption of Mt. St. Helens?

4. Suppose that you discovered

a fossil. Where did you fi nd it? What does it look like? What does it feel like? Is it a plant or an animal? Write a paragraph to answer these questions about your fossil.

5. Make Inferences If a fossil shows an animal with teeth that were not sharp, what do you think that animal ate?

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