Life Science Genre Comprehension Skill Text Features Science Content Nonfiction Cause and Effect Labels Captions Glossary Changing Ecosystems by Lillian Duggan Scott Foresman Science 5.6 ì<(sk$m)=bdjdbg< +^-Ä-U-Ä-U ISBN 0-328-13931-9
Vocabulary behavioral adaptation extinct inherit Changes in Ecosystems by Lillian Duggan mutation pesticide structural adaptation 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: (Bkgd) Christoph Burki/Getty Images Title Page: Bettmann/Corbis 2 Pat O Hara/Corbis 3 Runk/Schoenberger/Grant Heilman Photography 4 Royalty-Free/Corbis, Ted Spiegel/Corbis 5 Will & Deni McIntyre/Corbis 6 Yann Arthus-Bertrand/Corbis, Robert Dowling/Corbis 7 Getty Images 8 Jerry Young/ Dorling Kindersley 9 Michael & Patricia Fogden/Minden Pictures 10 Mitsuaki Iwago/Minden Pictures 11 Dan Guravich/Corbis 12 Thomas A. Ferrara/Corbis 13 Galen Rowell/ Corbis 14 Bettmann/Corbis 15 Art Wolfe/Photo Researchers, Inc. ISBN: 0-328-13931-9 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
How do ecosystems change? Animals Change Ecosystems Two animals that change their ecosystems quickly are locusts and beavers. Locusts travel in large groups called swarms and eat many plants. This takes food away from other animals and from people. Beavers make ponds by building dams. These dams stop streams from flowing. The ponds keep the beavers safe from predators. For other organisms the ponds may be helpful or harmful. Earthworms change their environment slowly. They dig holes in the soil that make it easier for plant roots to get oxygen. The worms leave digested material behind in the soil, making it healthier for plants. These are helpful changes. People Change Ecosystems People change ecosystems by bringing new plants or animals into them. These changes may be harmful to other species in the ecosystem. Zebra mussels were brought to the United States when they stuck to ships. Zebra mussels have no predators in this country. This has allowed the zebra mussel population to grow very quickly. The mussels have changed the ecosystems of many rivers and lakes. They take food and space away from other living things. Beaver dams may flood the homes of plants and animals. Zebra mussels stick to hard surfaces like these shells. 2 3
Landfills sometimes cover thousands of acres. People also change ecosystems by polluting the air or throwing out garbage. Americans produce about 200 million tons of garbage each year. That s about 1.8 kilograms per person every day! Most garbage is put into landfills. A landfill is a pile of garbage that is covered with soil and grass when it reaches a certain size. The ecosystem is changed while the landfill is being used. It might recover after the soil and grass are put on. At one time, pollution would leak out of landfills and flow into bodies of water. Modern landfills have special liners to keep pollution from escaping. Acid rain is rain that has absorbed air pollution. It pollutes soil and lakes, causing changes to ecosystems that can kill plants and animals. People sometimes fight this pollution by putting helpful chemicals into the water. People can treat polluted lakes by dumping helpful chemicals into the water. These trees have been damaged by acid rain. 4 5
How do species change? Inheriting DNA Heredity is the process in which plants and animals receive, or inherit, half of their genes from each parent. Offspring are different from their parents in some ways because they have different combinations of genes. But offspring will still look like their parents in most ways. The two dogs on this page have different color fur and eyes. But in most ways, they look almost the same. Traits That Are Not Inherited Some differences in organisms of the same species are caused by the environment. One organism might be larger than another because it lives in an environment with more food and water. The ecosystem can also affect an organism s color. The American flamingo gets its pink or red color from eating shrimp and other crustaceans. If it doesn t eat these animals, it will have white feathers. Flamingos are pink only if they eat certain foods. Different genes caused these dogs to have different colors of fur and eyes. 6 7
Adaptations Sometimes an organism s genes change. A change in genes is called a mutation. A mutation can pass from parent to offspring. Mutations can be helpful, harmful, or neither. Helpful mutations can lead to adaptations. Adaptations help an organism survive in its ecosystem. For example, some animals have colors that make it easy for them to hide. Adaptations are important when an ecosystem changes. Organisms that have the best adaptations have the greatest chance for survival. Structural Adaptations Helpful mutations may cause changes in body parts. A structural adaptation is a changed body part that helps an organism survive in its ecosystem. A hummingbird s long beak is a structural adaptation. It helps the bird get food from some flowers in its ecosystem. The first long-beaked hummingbirds passed the genes for this feature to their offspring. After many generations, lots of hummingbirds might have long beaks. When helpful adaptations get passed on in this way, it is called natural selection. This hummingbird s long beak is a structural adaptation. Green skin helps this frog to hide. 8 9
Behavioral Adaptations Do you think you could build a house without being shown how? Probably not. But when hummingbirds and other birds are born, they know how to make their own home and how to take care of their offspring. These behaviors are the result of genes passed from parent to offspring. A behavioral adaptation is an inherited behavior that helps animals survive. They are sometimes called instincts. Behavioral adaptations affect what an animal does. Lemmings are small rodents. If a population of lemmings gets too large, the lemmings migrate to another area. The instinct to migrate is a behavioral adaptation. Musk oxen have an instinct to circle around their young to protect them from predators. Not all animal behaviors are the result of behavioral adaptations. Some are learned. Lion cubs don t know how to hunt when they are born. Their parents teach them. Cubs stay with their mothers for 2 or 3 years while they learn to hunt on their own. Rough play with their parents and other cubs helps these lion cubs learn to hunt. 10 11
How do changes cause more changes? Changes in Behavior Sometimes new organisms move into an ecosystem. Sometimes the population of a species in an ecosystem changes. Changes like these can affect the behavior of other animals. A pet cat might change its habits when a new puppy is brought into its home. The cat may hide to avoid the puppy. Pesticides are sprayed to kill mosquitoes. Surprisingly, some hawks and falcons have begun to live in cities. Cities provide these birds with small animals to eat, water to drink, and tall buildings where they can build nests. Changes in Populations Mosquitoes spread diseases such as malaria and the West Nile virus. People try to kill mosquitoes by putting pesticides into their ecosystem. A pesticide is a poison that kills insects. Sometimes species adapt to changes in their ecosystems. Some populations of mosquitoes adapted to the pesticides. A few mosquitoes had genes that enabled them to live with the poison. They survived and reproduced, making more mosquitoes that can resist the pesticides. People take medicines called antibiotics to kill bacteria that cause diseases. Some bacteria have developed adaptations that keep them safe from antibiotics. When enough bacteria have these adaptations, the antibiotics can no longer prevent diseases. Scientists are always looking for new medicines to use when the old ones stop working. 12 13
The dodo became extinct around 1680 because of changes to its ecosystem. Many plants and animals that once lived on Earth are now extinct. Scientists study fossils to learn about extinct animals and the ecosystems they lived in. The bald eagle almost became extinct because of a pesticide called DDT. Rain washed the chemical into lakes and rivers, where it got into fish. When the eagles ate the fish, DDT got into their bodies too. The DDT made the shells of the eagles eggs thin. Many eggs broke before they could hatch, or they didn t hatch at all. The eagles did not adapt to the DDT. Because they could not produce many offspring, the bald eagle population became very small. When people stopped using DDT, the number of bald eagles started to increase again. Extinction Sometimes a species cannot adapt to changes in its ecosystem. Food may become limited because of a drought, a flood, a harsh winter, or the growth of a city. The species must move to another place to survive. If the species cannot move, its population will decrease. The species might even become extinct. A species that is extinct has no members of its kind alive. The dodo is a bird that became extinct more than 300 years ago. The dodos lived on an island. Sailors brought rats, pigs, and monkeys to the island. The dodos could not defend themselves against the new animals. They couldn t fly, so they were not able to escape. The bald eagle is the national bird of the United States. It almost became extinct because of a pesticide in its ecosystem. 14 15
Glossary behavioral adaptation extinct inherit mutation pesticide structural adaptation an inherited behavior that helps an animal survive when a species has no members left alive to receive genes from a parent a change in an organism s genes a poison that kills insects a change to a body part that helps an organism survive What did you learn? 1. Describe one way that people change ecosystems. 2. Explain why the American flamingo is pink. 3. Why are adaptations important for organisms? 4. Two types of adaptations are structural adaptations and behavioral adaptations. On your own paper, write to explain the differences between the two. Give examples from the book to support your answer. 5. Cause and Effect At one point the bald eagle almost became extinct because of a chemical called DDT. Explain how this happened. 16