interactions in ecosystems

Large animals such as bear, elk, and moose live in the taiga.. Desert plants have special parts that help them live without much water.. The small plants that do grow cannot provide enou

by Patricia Fitzhugh

Scott Foresman Science 5.5

Genre Comprehension Skill Text Features Science Content

• Captions

• Diagrams

• Glossary

Interactions

in Ecosystems

ISBN 0-328-13928-9 ì<(sk$m)=bdjcig< +^-Ä-U-Ä-U

Life Science

by Patricia Fitzhugh

Scott Foresman Science 5.5

Genre Comprehension Skill Text Features Science Content

• Captions

• Diagrams

• Glossary

Interactions

in Ecosystems

ISBN 0-328-13928-9 ì<(sk$m)=bdjcig< +^-Ä-U-Ä-U

Life Science

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3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

Vocabulary

community

cycle

ecosystem

energy pyramid

habitat

niche

population

What did you learn?

1 What are some living and nonliving parts of an ecosystem?

2 In what group of ecosystems do rivers, wetlands, coral reefs,

and the deep sea belong? What group is made up of forests, grasslands, deserts, and tundra?

3 Explain what a cycle in an ecosystem is Give at least

one example

that help them meet their needs On your own paper, write to explain how behaviors help organisms live in a biome where

it is very hot or very cold Include details from the book to support your answer

5 Predict Describe what might happen to a rainforest

ecosystem if its yearly rainfall decreased a great deal

Interactions in Ecosystems

by Patricia Fitzhugh

A community is a bigger part of an ecosystem A

community is all the populations in an area Members of a

community depend on each other for food and shelter

The nonliving parts of an ecosystem include air, water, soil, sunlight, and temperature These things often control what kinds of organisms—and how many—can live in an ecosystem

If a population’s needs are not met in an ecosystem, that population will get smaller Its members may not survive

2

What is an ecosystem?

Living and Nonliving Parts

Wherever there are living things, there are ecosystems An

ecosystem is all the living and nonliving things in an area

Living and nonliving things work together in ecosystems

A population is all the organisms of one species living in an

area at the same time This may be all the oak trees It may be

all the red ants

3

A biome is a large ecosystem Biomes are so large

that a single one may cover many countries The

climate and organisms are generally the same in all

parts of the biome

There are several kinds of biomes One kind is a

rainforest A rainforest biome has large amounts of

rain and thick plant growth

The United States has a rainforest biome in the

state of Washington This rainforest is a temperate

rainforest It receives a lot of rain, but can be

quite cool

Each living thing in an ecosystem has a niche

A niche is an organism’s role in an ecosystem For

example, the spotted owl has a niche in the temperate

rainforest It is a hunter The owl hunts and eats small

animals, such as mice

Each living thing also has a habitat A habitat is

where an organism lives The spotted owl’s habitats are

the trees and land where it lives

All the relationships in an ecosystem keep it

balanced For example, the populations of

mice and spotted owls balance each other

It works like this:

If the number of mice drops, the owls will have

less food So, the number of owls will drop, too With

fewer owls hunting, fewer mice will be eaten So, the

population of mice will grow Then owls will have

more mice to hunt So, the population of owls will

grow again

6 7

What are land

biomes?

Tropical Rainforest Biomes

Ecosystems near the equator are

always warm Some of them get a

lot of rain—more than three meters

each year In these places plant

populations grow large A tropical

rainforest results

Tropical rainforests have more

different kinds of life than any other

biome There may be dozens of

different species living in a single tree

Deciduous Forest Biomes

Deciduous forests grow in cooler areas They cover much of the eastern United States Oak, elm, and maple trees grow in these biomes These are deciduous trees That means that they lose their leaves when it gets cold This helps them save food and water

Some other organisms also change in colder seasons Bears sleep through much of the winter Snakes and frogs stay underground Some rabbits’ fur becomes snowy white This helps the rabbits blend

in with the snow They can easily hide from animals that hunt them

Organisms have structures that

help them survive The kinkajou’s

long tongue can get honey and

insects Its tail can grab onto

branches.

Grassland Biomes

Grasslands are biomes with many

types of grasses Grasslands do not get

much rain So few trees can grow in

these biomes

Grasslands once covered huge

areas of the midwestern United States

Then settlers came Over many years,

settlers turned most of the grasslands

into farms

Bison, antelope, and prairie dogs

live on the grasslands The changing

of this habitat into farms has affected

animal populations For example,

gray wolves once hunted prairie dogs

Farming reduced the prairie dog

population, so the wolves had less to

eat People also hunted the wolves

These changes caused the gray wolf

population to fall very low

Taiga Biomes

A taiga is a kind of forest biome Tiagas are found in areas that are cold and fairly dry They cover much

of Canada and Russia

Most trees that grow in the taiga have very thin leaves called needles Needles help trees live where it is cold, dry, or both They stay on the tree all year long so they are ready to make food as soon as warm weather arrives They have a waxy coating that helps the tree hold water

Large animals such as bear, elk, and moose live in the taiga Smaller animals such as porcupines and mice live there as well All these animals have fur It keeps them warm Ducks, owls, and woodpeckers also live in the taiga These animals have feathers to help keep them warm

Gray wolves once lived over most of North America Now wolves live in only a small part

of this area.

The moose is a very large animal found in the taiga.

10 11

Desert Biomes

Deserts are areas that get less than

25 cm of rain or snow each year

All deserts have low rainfall Many

deserts are very hot, but others are

cold most of the time Some deserts

have sand dunes and others are very

rocky Large deserts are found in

Africa, Asia, and Australia

Desert animals may include

rattlesnakes, lizards, jackrabbits, and

beetles Plants may include bushes,

grasses, and cactuses

Desert plants have special parts

that help them live without much

water Some have large root systems

close to the surface of Earth

These roots can take in

rainwater quickly

Desert animals have

special behaviors that

help them survive Many

animals rest during the

hot day Some animals dig

into the ground to keep cool

They look for food at night,

when it is cooler

Tundra Biomes

The tundra is a very cold biome It gets little rain Tundras lie in the far northern parts of the world Rodents, rabbits, and caribou live on the tundra Tundra animals may also include weasels, owls, and foxes

In any ecosystem, a population can only grow so large The number

of organisms that can live in a place is the carrying capacity If a population grows larger than the carrying capacity, there won’t be enough food, water, space, or shelter

Populations will have to move to another area to survive

On the tundra, cold weather makes it hard for plants to grow The small plants that do grow cannot provide enough food and shetler for animals This keeps the carrying capacity low

Emus are found

in many areas of Australia, including deserts.

When snow covers the tundra, caribou often move to warmer areas to find food

What are water

ecosystems?

Rivers

Many different animals live in

rivers They include fish, ducks,

turtles, and insects Some animals

live only in rivers that flow slowly

River ecosystems also include

animals that spend much of their

time on land The river otter,

for example, does well in both

environments In the

water, its sleek body lets

it swim fast to catch

fish While swimming,

it can close its nose and

ears On land, it can

run to catch frogs and

small mammals

Organisms that live

in rivers usually do not

also live in oceans The

ocean water is too salty

for their cells

Wetlands

There are many kinds of wetlands All are partly covered with water or flooded at least part of each year Florida’s Everglades is a wetland

It has huge areas of sawgrass that grows more than 3 meters tall

Alligators, fish, deer, and snakes live

in the Everglades

A swamp is a wetland with many trees and bushes Deer, otters, turtles, snakes, and wild pigs may live in swamps

Some wetlands are parts of estuaries These are places where rivers flow into the ocean Grassy wetlands called salt marshes are found in estuaries

Wetlands are helpful in many ways The plants, soils, and tiny organisms of wetlands often act as filters They clean water that flows through the wetland

The river otter can live

easily on the land or

in the water.

Crayfish are often found

in swamp ecosystems.

Coral Reefs

Coral reefs are

home to many types

of organisms These

include sharks, clams,

crabs, clownfish,

eels, and many

other animals

Corals are animals

They have a special

relationship with

algae Some algae need sunlight,

so they only grow in shallow water

These algae grow inside the coral

Other algea help the coral make

a hard outside coating Over time,

many corals grow and die Their hard

outside coatings pile up to make a

coral reef Many kinds of plants and

animals live in the reef

Corals grow well in warm water

with few nutrients and little oxygen

They are found near Florida,

Australia, and many other places

Coral reefs help to protect the shore

from storms They also provide us

with food and new types of medicine

The Deep Sea

Some very strange animals live in deeper areas of the ocean They must deal with cold, darkness, and very high water pressure These animals are well-suited to the pressure Some will die if they come to the surface, where water pressure is lower

Sunlight cannot reach these deep areas So, no plants can grow Many animals in the deep sea eat dead plants and animals that sink down Clams, crabs, and tubeworms live around vents in the deep sea Bacteria live there, too They make food

from chemicals in the water The bacteria themselves are food for larger animals

Jellyfish belong to the same phylum

as coral.

Tubeworms don’t have mouths or stomachs

Bacteria live inside the tubeworms and make food that they share.

15

14

How do organisms interact?

Competition

Organisms often compete for things they need They may

compete over space, food, or water Sometimes they compete

for their lives

Animals of the same species compete You may have heard

cats screeching outside as they fight for territory Animals of

different species also compete For example, rabbits and mice

in a desert community compete They compete to find plants

for food

Plants may compete for sunlight or for water The kudzu

plant is very successful at competing for light It covers other

plants, keeping them from getting any sunlight Plants with

larger root systems will take in water faster than other plants

Symbiosis

Symbiosis is a long–term relationship between different species One of the species is always helped The other might be helped, harmed, or not affected

The buffalo and the cattle egret have one kind of symbiosis

As the buffalo moves through the grass, it scares up insects The egret can catch the insects easily This helps the bird, but it doesn’t affect the buffalo

In another kind of symbiosis, very small organisms are fed as they help the buffalo digest its food Both species are helped The buffalo and worms show a third kind of symbiosis The worms live inside the buffalo They get food, but the buffalo may become weak or sick Organisms that feed on other organisms in this way are called parasites

In a fourth kind of symbiosis, one organism can’t survive without another Lichen is a fungus and an algae living together The algae makes food from sunlight The fungus could not survive without the food that the algae produces

Plants may compete for

sunlight Kudzu, shown

here, often covers other

plants in this competition

The relationship between the buffalo and the cattle egret is an example of symbiosis

18 19

How does energy

move in ecosystems?

Food Chains and Webs

All living things need energy to live They get energy from

food The organism that is eaten gives food energy to the

one that eats it Producers are organisms such as plants,

which make their own food They get energy from sunlight or

chemicals in nature Consumers are organisms that cannot

make their own food They must eat other organisms All

animals are consumers

When food is eaten, the energy in the food moves from one

organism to another Food energy moves in chains such as this:

sun ➝ plants ➝ snowshoe hare ➝ spotted owl ➝ bacteria

The diagram below shows many food chains combined in

one food web You can see an ecosystem more fully in a web

than in a chain That’s because consumers usually eat many

kinds of other organisms

Energy Pyramids

An energy pyramid is a diagram of a food chain It shows

the flow of energy from one level to the next The energy pyramid is widest at the base That’s because producers are shown at the base They have the greatest amount of energy in

an ecosystem

Look higher on the energy pyramid Notice that it gets narrower as it rises This shows that less energy flows through higher levels

An energy pyramid has more energy at its base than at its top This is because some energy is given off as heat by each organism in the pyramid.