Interactions in ecosystems

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.. Students know many plants d

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Genre Comprehension Skill Text Features Science Content

Nonfi ction Cause and Effect • Captions

• Diagrams

• Call Outs

• Glossary

How Living Things Survive

Scott Foresman Science 4.5

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 0-328-23553-9

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by Martin E Lee

Life Sciences

adaptation

community

competition

pollination

population

seed dispersal

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publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson.

ISBN: 0-328-23553-9

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Interactions

in Ecosystems

by Martin E Lee

What determines

survival?

Competition

All of the owls that live in an area make up a

population A population is all of the same kind of

living things that live in one place All of the different

populations in that place make up a community.

Animal populations may hunt together, travel

together, and protect each other But their environment

might not have enough resources Competition

happens when living things must use the same limited

resources Owls compete for food, shelter, and places to

hunt Mice compete for food and shelter from owls

Owls compete with other animals for food sources such as mice.

3

Plants also compete to stay alive Many seedlings may sprout close together But only a few grow into mature plants This is because there is not enough space for all of them Taller plants get more sunlight than shorter plants do This allows them to make more

of their own food through photosynthesis Their shorter neighbors in the shade may not be able to survive

Different populations in a community might compete Snakes, owls, and mice all share an area

The owls and snakes must compete for the same population of mice

This mistletoe competes with other plants by taking resources from the tree.

Sharing Resources

Both owls and hawks feed on the same kind of prey

Hawks do their hunting by day Owls hunt at night

This reduces competition between hawks and owls

Symbiosis is two living things needing each other to

live One kind of symbiosis is with lichens Lichens are

fungi and algae Algae supply food for the fungi Fungi

give algae water and protect them from sunlight

Symbiosis between living things can sometimes

help one while it hurts the other The organism that is

helped is called a parasite The one that is hurt is called

the host The mistletoe on page 3 is a parasite The tree

is a host

Black bears sleep for much of

the winter In the spring they

eat young plants and grasses.

5

A Varied Diet

Animals eat other living things to get the energy they need Some animals compete by eating different kinds of food Black bears eat in this way They eat whatever they can fi nd at different times of the year

Black bears eat grasses and meadow plants in the spring All summer they claw into logs and stumps for insects They eat pine cones, acorns, berries, and nuts

in late summer and fall They also eat fi sh Bears will even eat trash left out by humans if they can get at it

California’s black bears hunt for salmon in the late summer

Claiming and Defending Territory

Many animals compete for territory Territory is

an area where an animal fi nds its food and water It

provides space for living and raising young Territory

helps animals get the resources they need

Animals do many things to claim and defend their

territory Male crickets sing loudly and fi ght each other

for territory Male butterfl ies defend where they perch

Mammals, including male bighorn sheep, elk, and

deer, will crash their horns or antlers together to

compete for territory This also helps them

attract mates Skunks spray a smelly

substance on animals that get too

close The bad smell works!

This red-winged blackbird is

singing and spreading his wings

wide to defend his territory.

7

Birds also have many behaviors for claiming or defending their territory They may strut or sing Or they will spread their wings wide This makes them look threatening

The avocet is a shore bird Avocets work together to protect their nesting areas They make loud noises and rush away from the nest Such behavior may distract predators

An avocet spreads its wings as wide as possible This scares away predators.

Plants Compete for Resources

The desert has many creosote plants Creosote plants seem to

“claim” territory that other plants cannot survive in Their wide, shallow root system helps them soak up water quickly They soak

up so much water that other plants cannot grow!

How do

environmental

changes affect living

things?

An adaptation is a trait that helps an organism

survive in its environment Color change is an

adaptation In spring, the feathers of birds called

white-tailed ptarmigan are gray or brown They

blend in with plants In winter, these birds have white

feathers They are able to blend in with snow and ice

A change in the environment can cause problems

for living things Many birds migrate to California salt

marshes But people have drained or built over most

of these marshes This has reduced space for migrating

birds This makes it harder for birds to survive

A ptarmigan’s feathers change colors with

the seasons This makes it harder to see.

9

Whales’ Adaptations

Whales are adapted to life underwater Along with the adaptations shown in the picture, whales also have a special way to feed They push seawater out of their mouths through plates called baleen Baleen is like a fi lter It traps tiny living things called plankton

Plankton are the whale’s main food One of the largest animals in the world survives by eating tiny sea life!

Flippers, smooth skin, and a tail fl uke are adaptations that help whales swim.

Blubber is a thick layer of fats and oils under a whale’s skin

This adaptation keeps whales warm in cold water

How Plants Survive

Plants also have adaptations that help them

survive Pine trees have thin waxy leaves, also called

needles Pine needles do not lose much water Some

plants’ leaves or thorns are poisonous This protects

them from animals that would eat them

Pollination is the movement of plant pollen from

a male part of a fl ower to a female part Birds, bats,

and insects help fl owers pollinate They move the

pollen as they feed on the plants Bright fl owers and

sweet smells are helpful adaptations for plants They

attract the animals that pollinate

Skunk cabbage grows in shade

in moist forests Its large leaves

help it take in light.

11

Plants often change as the weather changes In winter, many plants stop using sunlight to make food Their leaves turn brown and drop off Some plants can store food in their roots, stems, seeds, or fruits These adaptations allow the plant to survive winter When spring returns, they can grow again

Plants compete for sunlight, water, nutrients, and living space In a group of the same kind of plant, some plants will get more nutrients than others This helps them grow taller Taller plants will get more sunlight This helps them make more food

These plants’ bright colors are an adaptation So are their thick leaves and stems

How do animals

depend on plants?

Food and Other Substances

Animals would starve without plants Some

animals do not eat plants But they get energy by

eating animals that eat plants

Animals live where they can fi nd the plants they

eat Monarch butterfl y caterpillars eat only milkweed

plants Many caterpillars spend the winter in parts of

California Milkweed is easy to fi nd in those areas

Milkweed plants contain a chemical The chemical

enters the monarch’s body as it eats This chemical tastes bad or even poisons other animals But it protects the butterfl y Other animals learn not to eat the butterfl y

This monarch butterfl y caterpillar gets its food from milkweed plants.

13

Some animals get other things they need by eating plants too Some desert animals survive by getting water from plants

Oxygen

You have read that plants use energy from sunlight

They use the energy with water and carbon dioxide to make their own food Plants also make oxygen when they make food They release the oxygen into the air

This oxygen is important to all living things People and other living things must have oxygen Oxygen helps living things get energy from the food they eat

This sheep would starve if the grass died out

It depends on grass for energy.

Shelter and Materials

Animals also use plants for shelter Some insects

stay protected by looking like part of a plant Many

animals in tropical rain forests live in the trees their

whole lives This helps them stay safe Fish and other

water animals stay away from danger by hiding in

plants Large bushes and cactus plants in the desert

give shade and shelter for snakes, lizards, and birds

Other animals use plants to build shelters of their

own Most birds build their nests from plant matter

such as leaves, twigs, and moss Beavers build dams

and homes from trees and branches

This hummingbird uses plant

fi bers, moss, lichens, and spiderwebs to build its nest.

15

Plants and People

People depend on plants for all kinds of materials

Trees provide us with wood for buildings and furniture

The paper this book is printed on was made from plant

fi bers The clothes you are wearing might be made from plants too! Many kinds of cloth are woven from plant fi bers such as cotton

Other fi bers, such as silk and wool, come from animals But it takes plants to feed those animals

Wool comes from sheep that ate grass and other plants The silkworms that spin silk fi bers eat the leaves of mulberry trees Everywhere you look, you will see something that came from a plant

Cotton cloth is made from cotton plants.

Yarn and linen cloth are made from the fl ax plant.

Plant Fibers

How do plants

depend on animals?

Pollen on the Move

Pollen is made in stamens Stamens are male parts

of fl owers Pollen has to get to the pistils for pollination

to happen Pistils are the female parts Some plants

need help from animals in order to pollinate

Flowers make a sweet liquid called nectar Bats,

bees, butterfl ies, and birds eat nectar They move from

fl ower to fl ower in search of it They are drawn by the

fl owers’ colors, smells, and shapes

Pollen rubs onto the animal’s body

as it eats the nectar It may then stick

to the pistil of the next plant the

animal visits Bees carry pollen

back to their hives

This bat helps certain plants pollinate.

17

From Fertilization to Food

Suppose a pollen grain lands on a pistil It may cause a thin tube to start growing down through the pistil Soon the tube reaches the pistil’s egg cells Then sperm cells from the pollen move down the tube

There they combine with the egg cells This is called

fertilization.

A fl ower goes through many changes after fertilization The petals and stamens dry up and fall off The fertilized egg soon develops into a seed

The bottom part of the pistil grows larger and becomes a fruit The fruit protects the seed or seeds

Many animals eat these fruits

This fl ower has a pistil and stamens The yellow part at the end of each stamen is pollen.

Seeds on the Move

Some plants scatter their seeds by spreading them

in the wind Others spread them on moving water

Many plants rely on animals to help Scattering seeds

is called seed dispersal.

Fruits protect seeds and attract hungry animals

Animals eat the fruit and leave the seeds behind This

often happens in a place where a seed can sprout

An animal may swallow plant seeds with the fruit it

eats The seeds may pass through its body without being

digested The seeds leave the animal’s

body with its other wastes Those

dropped seeds may sprout into

new plants that grow far from

the parent plant

Chipmunks, mice, and

squirrels bury seeds to

use later But some seeds

sprout before they are

dug up

The seeds stored by

chipmunks can sprout

before the chipmunks

eat them.

19

Seed Dispersal

Some seeds are inside prickly pods called burs

Burs have tiny hooks that catch on an animal’s fur

The animal carries the seed away when it moves

Eventually the bur will drop to the ground The seeds in

it may then grow into new plants

Seed dispersal helps plants in many ways Think of

a cherry tree Many new cherry trees might sprout if they fell near the adult tree But the tree and the seeds would compete for water, soil, nutrients, and sunlight, and the tree would get more of those things The tiny, crowded seedlings would not be able to grow Seeds have a better chance to grow if animals, wind, or water carry them away from their parent plant

The seeds from this dandelion fl oat in the wind like parachutes.

Ocean currents might carry this coconut seed many kilometers.

adaptation a trait that helps an organism

survive in its environment

community all of the different populations in

one place

competition two or more living things using the

same limited resources

pollination the movement of pollen from a male

part of a fl ower to a female part

population all of the same kind of living things

that live in one place

seed dispersal the process of scattering plant seeds

1 How are populations and communities related?

2 How do algae and fungi help each other live?

3 How do male bighorn sheep, elk, and deer compete for

territory and attract mates?

sources to write a report that answers this question: What adaptations do black bears have for staying alive?

marshes to change? What has been an effect of this?