Life Sciences Standards Preview Standard Set 3. Life Sciences 3. Adaptations in physical structure or behavior may improve an organism’s 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.
by Kim Fields
Genre
Nonfiction
Comprehension Skill
Make Inferences
Text Features
• Captions • Glossary
Science Content
Changing Environments
Scott Foresman Science 3.5
ISBN 0-328-23531-8
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Vocabulary competition extinct fossil habitat
by Kim Fields
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Living 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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Changes 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. Beavers change the environment when they build dams.
This change helps plants and animals that need still water. Dragonflies can live in this new environment. Also, the trees the beavers cut down no longer shade the ground below. Small plants and shrubs that benefit 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 fish. The pond harms plants and animals whose homes are flooded. Trees needed to make the dam are also lost.
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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.
Changes Caused by People All 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!
Helpful and Harmful Change
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Changes 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 Change Some changes happen in a cycle. Scientists believe a change in the weather affects small fish called sardines. The overall weather around Monterey Bay changes in a fifty-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.
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Changes in The Environment Affect Living Things Too 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.
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 Water Too much water at the same time can change an environment. Storms can cause flooding. Floods can wash away peopleâ&#x20AC;&#x2122;s homes. Floods can also wash away plants and soil. Animals, including snakes, can lose their homes to flooding. Floods carry thick blankets of mud to different places. Flooding in Linda, California
A dry season in Imperial Valley, California
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Volcanic Eruption
After the Eruption
In 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 flood. 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.
Some shrubs and plant roots covered by snow survived the eruption. Seeds carried by the wind sprouted and grew. As plants grew, more animals could find 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 wonâ&#x20AC;&#x2122;t 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.
In 1980, Mt. St. Helens erupted.
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Wildfire
After a Fire
A wildfire brings a huge change to a forest. When lightning strikes a tree in the forest, it can set the forest on fire. Then the fire rushes through the forest. Small plants and dead brush burn. Trees with thick bark live through the wildfire. Other trees may burn down. This creates open spaces in the forest.
Animals 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, flowers, 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 animalsâ&#x20AC;&#x2122; homes. Many living things die. Wildfires are also helpful for many plants and animals. They clear out the forest floor. New trees and plants have more space to live. The ash makes the soil healthy, helping plants to grow.
The temperature of a wildfire can reach 800°C.
Young trees grow with plenty of living space and sunlight.
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Comparing Living Things to Those Of Long Ago Fossils 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 Earthâ&#x20AC;&#x2122;s 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.
What Fossils Tell Us Fossils 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 find 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
This is a fossil of a giant wombatâ&#x20AC;&#x2122;s jawbone.
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Plants Change over Time The first plants did not have cones or flowers. 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 flowers 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 first magnolias kept their leaves yearround. 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 flowers and leaves of the magnolias are like those that lived a long time ago. The flower of the magnolia has stayed nearly the same for 100 million years.
Magnolia leaf fossil
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Animals Change over Time Fossils 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 find out what they ate. Scientists in England assembled an 84-foot-long dinosaur skeleton.
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 find 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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Glossary competition
when two or more living things need the same resources
What did you learn? 1. How can beavers harm the environment when they build dams? 2. How can dry weather affect animals?
extinct
no longer lives on Earth
fossil
the remains or mark of a living thing from long ago
habitat
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3. How did some plants survive the eruption of Mt. St. Helens? 4.
Suppose that you discovered a fossil. Where did you find 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.
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Make Inferences If a fossil shows an animal with teeth that were not sharp, what do you think that animal ate?
the place where a living thing makes its home