Living things change

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.. S

Genre Comprehension Skill Text Features Science Content

Nonfi ction Make Inferences • Captions

• Glossary

Changing Environments

Scott Foresman Science 3.5

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.

ISBN 0-328-23531-8

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by Kim Fields

Life Sciences

competition

extinct

fossil

habitat

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by Kim Fields

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

3

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.

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

TK

Beavers change the

environment when they

build dams.

5

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

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!

TK

7

Helpful and Harmful Change

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 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.

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

A dry season in Imperial

Valley, California

9

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 fl ooding Floods can wash away people’s 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

Volcanic 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 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.

11

After the Eruption

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 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 won’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.

Wildfi re

A 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 800°C.

13

After a Fire

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, 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.

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 Earth’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

This is a fossil of a giant

wombat’s jawbone.

15

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 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

Plants Change over Time

The 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

17

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

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 fi nd out what they ate

Scientists in England

assembled an 84-foot-long

dinosaur skeleton.

19

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

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

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?

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.

teeth that were not sharp, what do you think that animal ate?