Plants and Animals in Ecosystems

Life Sciences
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.c. Students know many plants
depend on animals for pollination and
seed dispersal, and animals depend on
plants for food and shelter.
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.
Genre
Nonfiction
Comprehension Skill
Cause and Effect
by Catherine Quirin
Text Features
• Captions
• Diagrams
• Glossary
Science Content
How Living Things
Survive
Scott Foresman Science 4.5
ISBN 0-328-23554-7
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Vocabulary
adaptation
community
competition
pollination
population
seed dispersal
Plants and Animals
in Ecosystems
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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
in one place. A community is made up of all the different
populations living in that place.
Some populations work together to find 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.
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.
This sidewinder snake must
compete for food.
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Animals Sharing
Eating Different Foods
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.
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 fish. 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.
The yucca moth and Joshua
tree live in symbiosis.
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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 fly safely away.
The killdeer to the left is trying to scare
away predators. The one below is
pretending its wing is broken.
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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 flap and ruffle 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,” “ruffle 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.
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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
their environments. An adaptation is a trait that helps an
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 difficult to see. These color changes
are an adaptation to the environment.
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.
Adaptation
In the fall, the long-tailed
weasel’s brown fur matches
the log and leaves.
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In the winter, its white fur
matches the snow.
As the diagram shows, whale
blubber is very thick. It keeps
whales warm in cold water.
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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 find water deep underground.
These cactus plants have adaptations that
help them live in dry desert environments.
In order to grow seeds, flowering plants must be
pollinated. Pollination is the movement of plant pollen
from a male part of a flower to a female part. Birds, insects,
and bats help pollinate plants. Plants often have sweet
smelling or bright flowers. 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 butterfly
help pollinate plants.
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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.
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
fibers such as cotton.
Kangaroo rats eat the
seeds of creosote bushes.
A gilded flicker bird
uses a cactus as its
nesting place.
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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 flower’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, butterflies, and birds
eat nectar. These animals go from flower to flower trying to
find nectar. The colors, smells, and shapes of the flower 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.
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
flower 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.
Fertilization Process
The bee gets nectar from the
flower. It carries pollen from
plant to plant.
The rose attracts
bees for pollination.
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After fertilization,
the petals drop off.
Seeds develop and
grow into a fruit.
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How Seeds Move
Some seeds just sprout where the plant drops them.
Scattering seeds, or seed dispersal, can be more difficult.
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.
Birds sometimes scatter seeds by flying 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 flies away with the fruit,
it will help the plant scatter its seeds.
This dandelion is scattering its
seeds into the wind. This is a
type of seed dispersal.
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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.
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.
Burs can stick to a dog’s fur. When they
drop off, they might grow into a new plant.
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Glossary
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 flower 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
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What did you learn?
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?
4.
Using information from the librarymedia 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?