Plants and animals in ecosystems

Students know many plants depend on animals for pollination and seed dispersal, and animals depend on plants for food and shelter... Animals get food, water, and space to live from thei

Genre Comprehension Skill Text Features Science Content

Nonfi ction Cause and Effect • Captions

• Diagrams

• Glossary

How Living Things Survive

Scott Foresman Science 4.5

Standards Preview

Standard Set 3 Life Sciences

3 Living organisms depend on one

another and on their environment for

survival As a basis for understanding

this concept:

3.b. Students know that in any

particular environment, some kinds of

plants and animals survive well, some

survive less well, and some cannot

survive at all.

3.c. Students know many plants

depend on animals for pollination and seed dispersal, and animals depend on plants for food and shelter.

ISBN 0-328-23554-7

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Life Sciences

by Catherine Quirin

adaptation

community

competition

pollination

population

seed dispersal

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ISBN: 0-328-23554-7

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by Catherine Quirin

How do living things

survive?

Have you ever seen a squirrel scurrying through the trees?

You may have seen just one squirrel, but you can be sure there

are more nearby All of those squirrels make up a population

A population is all of the same kind of living things that live

populations living in that place

Some populations work together to fi nd food, travel, and

protect each other from predators Populations also must

live with limited resources This causes competition

Competition occurs when two or more living

things must use the same limited resources In Southern

California’s Mojave Desert, sidewinder snakes hunt rodents

Many sidewinder snakes compete for the same rodents

This sidewinder snake must

compete for food.

3

Different Kinds of Competition

Plants compete for resources too A lot of seedlings may sprout close to each other But very few will become adult plants There is not enough space for all of them The taller plants will do better than the shorter ones They can get more sunlight, which means they can make more food

Competition may also occur between different populations

in a community Sidewinder snakes are not the only desert animals that eat the Mojave Desert’s small rodents Barn owls and bobcats prey on the rodents as well These predators must all compete for the same populations of rodents

This owl competes with the sidewinder snake for mice.

Animals Sharing

Cactus wrens and desert bats both eat insects The wrens

hunt during the day, while the bats hunt at night This reduces

competition It helps the wrens and bats share resources

The yucca moth and Joshua tree share resources through

symbiosis The moth helps the Joshua tree grow new seeds

through pollination, which you will read about later It lays

its eggs in the tree’s seedpods The moth larvae eat the seeds

when they hatch The moth helps the tree grow In return, its

young get food

Symbiosis sometimes helps one organism while hurting

the other The one that is helped is called a parasite The one

that is hurt is called a host Spider mites are a parasite They

take nutrients from the leaves of trees

The yucca moth and Joshua

tree live in symbiosis.

5

Eating Different Foods

As you know, animals are consumers They eat other organisms to survive Some animals reduce competition by eating more than one kind of food Quails in California eat the seeds of grasses, shrubs, trees, and cacti Golden eagles have been known to eat small animals, reptiles, birds, and fi sh Gray foxes prefer small mammals But they will eat eggs, insects, birds, acorns, and fruit when they are hungry The less animals have to share the same resources with each other, the better their chances are for survival

Eating both insects and cactus fruit helps the desert bat survive.

Animals and Territory

Many animals compete for territory Territory is the area

where an animal lives Animals get food, water, and space to

live from their territory By claiming and defending territory,

animals can more easily get the resources they need

Animals have special ways of protecting their territory

from others in their population and from predators in their

community When a predator threatens a killdeer’s nest or

young, the adult bird pretends to be injured It hobbles along

the ground dragging its wing so that it looks broken Usually,

the predator will follow the bird Once the killdeer has led the

predator away from the nest, it will fl y safely away

The killdeer to the left is trying to scare away predators The one below is pretending its wing is broken.

7

Sandhill cranes have a different way of protecting their territory They will stand straight and walk in a way that is like a soldier on parade When they feel threatened they will also fl ap and ruffl e their feathers, stomp the ground, and make sounds such as snorts or growls

When a sandhill crane is frightened by a nearby predator,

it spreads its wings, sticks out its body as if it were about to attack, and walks toward the predator At other times it will

go into a “crouch threat,” “ruffl e threat,” or “charge.” These are names scientists use to describe how a sandhill crane behaves when it feels threatened

When their territory is safe again, male and female sandhill cranes give a special call The female crane makes a noise that sounds like a bugle Then the male joins

The sandhill cranes to the right are making warning calls The ones below are acting

as if they are threatened.

Living Things and

Environmental Change

Organisms can survive better in some environments

than in others For example, you will not see a sidewinder

snake in a rain forest Organisms must have adaptations for

organism survive in its environment

White-tailed deer are reddish-brown in summer and fall

In winter, they change to a grayish-brown color This color

almost matches the color of the tree bark in the surrounding

forests It makes the deer diffi cult to see These color changes

are an adaptation to the environment

In the fall, the long-tailed

weasel’s brown fur matches

the log and leaves

Adaptation

In the winter, its white fur matches the snow.

9

It can be hard for living things if the environment changes

One kind of sea bird lives only in the redwood forests of California When redwoods are cut down, these birds have less space to live in

How Whales Are Adapted

Whales are adapted to life underwater They have a thick layer of fats and oils called blubber This is an adaptation that helps them keep warm in cold water

Whales are also adapted to eating in the water Some kinds of whales have plates in their mouths called baleen

When they squeeze seawater out of their mouths, tiny organisms called plankton get trapped in the baleen

As the diagram shows, whale blubber is very thick It keeps whales warm in cold water.

Plant Adaptations

Plants also have adaptations that help them live in their

environment Desert plants have many adaptations that help

them survive in a dry climate Cactus plants have adaptations

that allow them to store and conserve, or save, water For

example, they do not have many leaves The water in leaves

evaporates into the air quickly Without leaves, the cactus

plants can save water Some desert plants have also developed

very long roots that can fi nd water deep underground

These cactus plants have adaptations that

help them live in dry desert environments.

11

In order to grow seeds, fl owering plants must be

from a male part of a fl ower to a female part Birds, insects, and bats help pollinate plants Plants often have sweet smelling or bright fl owers This adaptation helps attract the animals that pollinate plants When they go to use the plant for food, they also pollinate it

Many plants also change when the weather changes For example, some plants stop using sunlight to make food when winter arrives Their leaves turn brown, red, yellow, or purple, and then drop off Some plants use their roots, stems, seeds, or fruits to store food By doing this, the plant can survive if the environment changes Once the environment returns to the way it was, the plant can grow again

Insects such as this butterfl y help pollinate plants.

Animals Need Plants

Not all animals get their energy from plants But all

animals need plants to survive Animals that do not eat plants

get their energy from animals that do eat plants

Animals live in places where the plants they eat grow

The kangaroo rat only lives in deserts It feeds on seeds from

grasses, mesquite, and creosote bushes There is often very

little water in the kangaroo rat’s environment The rat makes

up for it by getting water from the seeds it eats

Plants use sunlight, water, and carbon dioxide to make

their own food In the process, they release oxygen into the

air Oxygen is important to living things, including people

Living things use it to get energy from the food they eat

Kangaroo rats eat the

seeds of creosote bushes.

13

People and Animals Using Plants

Plants also provide shelter Many animals hide in plants

Some insects even hide by looking like a part of a plant! In deserts, large bushes and cactus plants give animals such

as lizards, snakes, and birds shade and places to live

Birds use twigs, moss, leaves, and other plant parts to build nests The cactus wren builds its nest from dry grasses It adds an outer layer of thorny twigs to protect against predators

People depend on plants as well We use trees for lumber to build homes and furniture Some plants provide us with tasty fruits and vegetables Finally, many clothes are made from plant

fi bers such as cotton

A gilded fl icker bird uses a cactus as its nesting place.

Animals Help Plants

Many plants need animals to survive as well For example,

some plants need animals to help pollinate them Pollen is

made in a fl ower’s stamens These are the male parts of a

plant For pollination to happen, pollen has to get from the

stamens to the pistils

Flowers make a sweet liquid called nectar to lure animals

to them Animals such as bats, bees, butterfl ies, and birds

eat nectar These animals go from fl ower to fl ower trying to

fi nd nectar The colors, smells, and shapes of the fl ower draw

the animals to the nectar within them Pollen rubs off on the

animal’s body when it eats the nectar Then the pollen might

stick to the pistil of the plant the animal goes to next

The bee gets nectar from the

fl ower It carries pollen from plant to plant.

15

Fertilization

When a pollen grain lands on a pistil, it starts growing a thin tube The tube grows from the pollen down through the pistil The pollen tube then gets to the egg cells inside the pistil The pollen releases sperm cells into the tube These cells

combine with the egg cells in a process called fertilization.

How does a plant make a pear or an orange? After the

fl ower is fertilized, it changes a lot The petals and stamens dry up and fall off Then the fertilized egg changes into a seed

The bottom of the pistil gets bigger and becomes a fruit The seed or seeds are protected by the fruit

The rose attracts bees for pollination.

After fertilization, the petals drop off.

Seeds develop and grow into a fruit.

Fertilization Process

How Seeds Move

Some seeds just sprout where the plant drops them

Some plants spread seeds using wind or water, but most need

the help of animals

Many fruits not only protect seeds, but also attract animals When animals eat the fruit, they often leave the seed in a place where it can grow

This dandelion is scattering its seeds into the wind This is a type of seed dispersal.

17

Birds sometimes scatter seeds by fl ying away with the fruit before eating it Some animals, such as mice and other rodents, bury seeds to eat later The buried seeds might sprout before the rodents have eaten them

Animals may also swallow the seeds when they eat the fruit If the animal does not digest the seeds, they are part

of the animal’s waste Then a new plant can grow from the undigested seed

When the bird fl ies away with the fruit,

it will help the plant scatter its seeds.

More Ways of Carrying Seeds

Animals can even carry seeds they do not eat Some

seeds are in prickly pods called burs Burs can get stuck in an

animal’s fur Eventually the seed will drop to the ground and

grow into a new plant

Other seeds may be carried by the wind or the water

Milkweed seeds have tufts of silky hairs at their tops The

hairs act like little parachutes, carrying the seeds on the wind

until they drop somewhere else Mango seeds can be carried

by the ocean until they wash up on shore and sprout

Burs can stick to a dog’s fur When they drop off, they might grow into a new plant.

19

You may be wondering why plants need adaptations for seed dispersal Suppose all the seeds of an evergreen tree fell

to the ground right under the tree Many new trees might sprout up But the new trees would have to compete with the parent tree and the other seedlings for water and nutrients

The parent tree’s roots would get more of water and nutrients from the soil than the new trees could It would also get more sunlight than the new trees could The new trees would be unable to grow As you can see, seeds are much more likely to grow if animals, wind, or water carry them to other places

The young tree is able to grow because

it is away from the parent tree.

environment

limited resources

of a fl ower to a female part

live in one place

seed dispersal the process of scattering plant seeds

1 What adaptations do cactus plants have for their

environment?

2 How do insects, birds, and bats help plants survive?

3 In what ways do animals depend on plants?

library-media center or other sources, choose one plant and one animal that live in the same place Then write a report about the adaptations they have for surviving in that place

5 Cause and Effect What could cause a decrease in the

population of cactus wrens in an area? What effect might fewer cactus wrens have?