3 5 living things in a world of change (life sciences)

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.. I

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 0-328-23530-X ì<(sk$m)=cdfdai< +^-Ä-U-Ä-U

by Trish West

Life Sciences

competition

extinct

fossil

habitat

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Illustration

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ISBN: 0-328-23530-X

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by Trish West

How do living

things change their

environment?

Changing the Environment

A habitat is a place where a living thing

makes its home Living things get what they need

from their habitat

A habitat is like a balance On one side of the

balance are the things that live in the habitat

On the other side are the things that the habitat

provides If the balance has equal things on both

sides, plants and animals can live and grow there

3

Change can tip the balance For example, trees

in a forest need sunlight to grow If there are too many trees, they can’t all get sunlight Some trees may die When two or more living things need the

same things, they are in competition.

Sunlight helps these young trees grow

Beavers Causing Change

Animals change their environment by building

homes A beaver cuts down trees with its sharp

teeth It builds a dam The dam holds back moving

water The blocked water forms a pond for the

beaver’s home

The dam is good for animals that like to live

in still water It gives them more places to live

This change is not good for animals that live in

moving water

This change affects plants too The trees that are

cut down no longer shade the area Other plants

get more sunlight They have room to grow

Beavers build homes and dams from mud and

sticks The beavers change the environment

5

Humans Causing Change

People need shelter just as other living things

do People make room for their homes They may cut down forests for wood They may also plow

up grasslands for farms These changes affect the environment Sometimes people and animals compete for living space

People have changed the environment by building homes and farms They may now be competing with animals for space.

Plants and Algae Causing Change

Changes can help some living things and hurt

others For example, someone brought purple

loosestrife to the United States Animals here don’t

eat it It keeps growing in more places Now there is

less room for plants that lived here fi rst

Fertilizers also change the environment Farmers

use them to help their crops grow Some fertilizers

wash into streams Tiny algae live there Fertilizers

help the algae grow If they grow too much, the

algae block sunlight Some algae die Tiny living

things that eat the dead algae grow in number

They use up the oxygen that fi sh need Fish die or

move to a new habitat

Purple loosestrife

compete with

other plants.

7

A Pattern of Change

Some changes repeat in a cycle For example, small mammals called lemmings eat tundra plants When there is a lot of food, there are more lemmings After lemmings eat most of the plants, there is less food Many lemmings leave Then the plants can grow back This fi nishes the cycle The cycle is then repeated

Lemmings cause changes that can repeat in a cycle.

How do changes in

the environment

affect living things?

Too Little Water

Periods of dry weather change environments

People can also make places dry They may use too

much water for their homes and farms Then lakes

and streams will not have enough water for animals

and plants Animals die or move away

During a dry season, some plants can

survive by using less water Others die.

9

A place may get drier over thousands of years

Shrubs and grasses adapted to using less water may replace trees that need more water The animals in a place can also change Animals that use shrubs and grasses for homes and food replace animals that use trees

Too Much Water

Living things need water However, too much water all at once can change an environment

Storms can cause fl oods Floods wash away animals’ homes Floods also wash away soil and plants Floods spread thick blankets of mud

Animals may die, live, or move away

When the Mississippi River fl oods, it can carry seeds and mud to new places.

<PHOTOS: Pick up photo of eruption on SE page 164.>

10

Volcanic Eruption

In the spring of 1980, Mt St Helens erupted in

Washington State One side of the volcano broke

away Hot rocks and gases melted snow and ice

The area was fl ooded The volcano shot out a cloud

of ash Winds carried the ash around the world

The blast changed the environment Mud

covered huge areas In some places, ash piled

up a meter thick The forests on Mt St Helens

were destroyed

11

After the Eruption

Not all living things on Mt St Helens died during the eruption Seeds hidden in the soil sprouted and grew Wind blew seeds from other places

Animals that lived underground also survived

These ants, spiders, mice, and gophers were protected from the blast Birds came back to live in dead trees Mice, shrews, and voles also returned

The weasels that ate these animals returned, and

so did large elk

Each change in the environment brought back different kinds of plants and animals to the mountain The environment won’t be the same as

it was for a long time But the mountain is fi lled with life again

Only a few plants survived the eruption

of Mt St Helens.

Wildfi re

Lightning can strike a tree in a forest This can

cause a wildfi re The fi re races through the forest

Dead brush and small plants burn Some trees

with thick bark survive A fi re brings big changes

to a forest

Forest fi res bring both harmful and helpful

changes Animals and plants die They lose their

homes However, fi re clears the forest of dead wood

It also makes more living space Ash makes the

soil healthy for plants to grow Fire often creates

habitat for more kinds of living things

Before a fi re, trees and other plants

crowd the forest.

13

Animals have fewer places to hide in a burnt forest Their enemies can hunt them more easily

Birds can fi nd seeds on the open ground New seeds are carried in by wind and animals Plants that are adapted to strong sunlight grow They prepare habitat that trees need to grow Soon, the forest returns

A forest fi re can get as hot as 800°C.

How do living

things compare to

those of long ago?

Fossils

An environment may change more quickly

than a kind of living thing can adapt The change

can cause these plants and animals to go extinct,

or to no longer be living on Earth

Many plants and animals have become extinct

over time They no longer exist, but we can study

the fossils that are left behind A fossil is the

remains or mark of a living thing from long ago

This is the fossil

of an extinct

fl ying animal

15

What Fossils Show

Fossils hold clues about extinct plants and animals Fossils tell something about the environments these plants and animals once lived

in Fossils show changes in those environments

Fossils help show how extinct plants and animals are similar to living ones

This is a fossil of a fern that lived 350 million years ago.

This fern looks like many extinct ferns It grows today in Redwood National Park in California.

Changes in Plants over Time

Plant fossils show us that the fi rst plants were

different They did not have cones or fl owers Many

of them looked like today’s ferns As Earth changed

over time, so did the fi rst plants Trees that made

cones appeared Then fl owering plants appeared

Many of these are no longer living

Today, many magnolia leaves still look a lot like this fossil

17

One group of fl owering plants that has survived are magnolias When they fi rst appeared, the

world was warm and wet Magnolia trees had large

fl owers and leaves that they kept all year Today, magnolias like this are still alive

Some places where magnolias live have cold winters now The magnolias in these places lose their leaves in fall Their leaves and fl owers, however, are still similar to the early magnolias

The magnolia fl ower hasn’t changed for 100 million years!

Some magnolia trees have fl owers that bloom all at once.

Changes in Animals over Time

We can use fossils to learn how animals and the

places in which they lived have changed over time

Animals’ teeth, for example, are adapted to eating

certain kinds of food Meat-eating animals have teeth

that cut and tear Plant-eating animals have teeth

that grind only Comparing teeth of living things to

those of dinosaurs shows what dinosaurs ate

The Badlands in South Dakota used to be warm and

wet all the time Today they are almost a desert

19

Fossils of Tyrannosaurus rex have been found in

the dry Badlands of South Dakota This dinosaur probably used its sharp teeth to tear meat from the animals it hunted Other dinosaur fossils found have grinding teeth These dinosaurs must have eaten plants

Fossils of trees that lived in swamps have also been found in the Badlands The area does not have many plants today But all these fossils show how the Badlands must once have been a warm, wet place with many plants

Dinosaurs such as this T rex

have been extinct for about

65 million years.

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 What does a living thing get from its habitat?

2 What can fossils tell us?

3 How can fertilizers change an environment?

has changed the environment It could be a fl ood, a drought, a wildfi re—even new buildings Write a description of how the environment changed How were plants, animals, and people affected?

sticks, and mud across a stream A pond has formed behind the dam What kind of animal might live nearby?