FOCUS ON EARTH SCIENCE (15)

Living things interact with each other and with >ˆ˜Ê`i> Living things and nonliving factors, such as air, water, sun-light, and soil, interact in and the types of life they support defin

A D 1 1770 1840 1860 1880 1900

Field of Flowers California

pop-pies cover this meadow in Antelope

Valley, at the poppy reserve This is

the most consistent poppy bearing

Ecology and Resources

1861

First oil well

in California is drilled by hand

in Humboldt County.

1874–1892

John Muir writes about the natural beauty of northern California, leading

to the establishment of Yosemite National Park

347

Chinese drill oil wells as deep as

240 m using bits attached to bam- boo poles.

1770s

Jan Ingenhousz covers how plants react to sunlight;

dis-this leads to standing of photosynthesis.

under-August 1859

Edwin L Drake drills first oil well

in the United States in Titusville, Pennsylvania.

510

To learn more about ecologists and their

1996–2005

Scientists climbing redwoods to measure their height discovered hemlock trees, huckleberry bushes, and small sea animals liv- ing in the tops of the redwoods.

1931

Construction begins

outside Las Vegas to

dam the Colorado

River Hoover Dam

was the largest dam

at the time.

1957

First full-scale nuclear power plant in the world goes into service at Ship- pingport, Pennsylvania.

March 2005

Solar power station

in Morocco projected

to meet energy demands by 2008.

511

these events and others, visit

ca6.msscience.com

ca6.msscience.com

Ecological Roles

This environment is located in the Sierra Nevada mountain range in California It is characterized

by plants that are specially adapted to survive a drought season It also

supports native animals, like these gray foxes that were once common

throughout California, but are now isolated to these areas.

-Vˆi˜ViÊÊ+PVSOBM

-Vˆi˜ViÊÊ+PVSOBM Write three questions you have about this photo that

you might like to explore further.

Living things interact with

each other and with

>ˆ˜Ê`i> Living things

and nonliving factors,

such as air, water,

sun-light, and soil, interact in

and the types of life

they support define

biomes on Earth

Ecolog-ical roles are the same

in different biomes but

may be filled by

differ-ent species

4.a, 5.e, 7.c

5.c, 5.d, 5.e, 7.a, 7.b, 7.d

Visit to:

▶ view

▶ explore Virtual Labs

▶ access content-related Web links

▶ take the Standards Check

Start-Up Activities

513

How tangled is

the life web?

How many things affect an

animal? The sunshine and the

air affect it It may eat plants

and animals Think of an

ani-mal Where does it live? What

is that area like?

Procedure

1 Write the name of an animal in a circle in

the center of a blank sheet of paper

2 Write things in the environment that

affect the animal every day in circles

Connect them to your animal

3 Include interactions of the living and

non-living factors that affect your organism

Think About This

• Determine if the animal lives in water,

soil, or trees

• Imagine that a factor has suddenly

disap-peared from the animal’s life How would

your animal survive without it?

STEP 1 Collect two sheets of paper and

layer them about 2 cm apart vertically Keep the left edges even

STEP 2 Fold up the bottom edges of the

papter to form 3 equal tabs Crease the fold

to hold the tabs in place

STEP 3 Staple along the fold Label as

Abiotic Factors Make the following Foldable to identify the abiotic factors

in an ecosystem

5.c, 7.h

ca6.msscience.com

ELA6: R 2.4

Learn It! When you make inferences, you draw conclusions that are not directly stated in the

text This means you “read between the lines.” You

inter-pret clues and draw upon prior knowledge Authors rely

on a reader’s ability to infer because all the details are not

Human activities can

impact population size and

therefore affect entire

biomes. For example, if

people did not allow fires to

burn in chaparrals, there

would be no young pine trees

As older trees die, they would

not be replaced The animals

that depend on the trees for

food, shelter, and space would

either die or move elsewhere.

Text Question Inferences

Human activities

What human activities?

Resource use?

Population size

How can human activities affect population size?

Death rates are high? Birth rates are low?

Populations move?

affect entire biomes

How can it affect biomes?

Causes changes

to abiotic factors? Biotic factors?

Target Your Reading

Use this to focus on the main ideas as you read the chapter.

below on your worksheet or on a numbered sheet of paper

• Write an A if you agree with the statement.

• Write a D if you disagree with the statement.

you’ve changed your mind about any of the statements

• If any of your answers changed, explain why

• Change any false statements into true statements

• Use your revised statements as a study guide

1 A park in the city can be an ecosystem

2 Animals, such as cats and dogs, use energy from the Sun to make food

3 Earth is colder near the poles because it usually

is cloudy

4 Water moves through cycles

5 Every organism in an ecosystem depends on other organisms

6 Populations of organisms can grow without limits

7 More species of organisms live in tropical rain forests because of the wet, warm climate

8 There are six major zones on Earth that support different ecological communities

9 There are many trees in the polar tundra

10 Each species can fill many different roles in an ecosystem

Before You Read

LESSON 1

Figure 1 A patch of weeds is an ecosystem

Identify the interactions that may exist in this ecosystem.

516 Chapter 12 • Ecological Roles

Abiotic and Biotic Factors

Real-World Reading Connection What do you think of

when you hear the word ecosystem? Perhaps you imagine a

tropical rain forest with monkeys swinging from vine to vine, or California’s Mojave Desert, with coyotes searching for food These are examples of ecosystems, but ecosystems can be much smaller and closer to home

What is an ecosystem?

An ecosystem consists of living things, called organisms,

and the physical place they live There are many types of ecosystems on Earth—coral reefs, woodlands, and ponds

The patch of weeds shown in Figure 1 may not seem like an ecosystem But if you look closely, you may find insects eat-ing the plants or using them for shelter Robins and other birds may be searching for earthworms and other food

Organisms in an ecosystem interact with each other as well

as with nonliving parts of their environment

Reading Guide

What You’ll Learn

▼Explain how abiotic

factors including light,

temperature, air, water, and

soil influence living things

▼Describe how systems

depend on biotic and

abiotic factors.

Why It’s Important

Changes in living and

nonliving factors can affect

climate: the long-term

average of the weather

patterns of an area (p 483)

Science Content

Standards

4.a Students know the sun is the major

source of energy for phenomena on Earth’s

surface; it powers winds, ocean currents,

and the water cycle.

5.e Students know the number and types

of organisms an ecosystem can support

depends on the resources available and on

abiotic factors, such as quantities of light

and water, a range of temperatures, and soil

composition

7.c Construct appropriate graphs from

data and develop qualitative statements

about the relationships between variables.

Figure 2 The climate is colder at the

poles than the equator At the poles,

the Sun’s energy is less intense

because it reaches Earth at an angle

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Lesson 1 • Abiotic and Biotic Factors 517

Abiotic Factors

Abiotic factors are the nonliving parts of an ecosystem

Suppose you want to grow a plant in your classroom You

could plant a seed in a pot of damp soil and place the pot on

a sunny windowsill What are the factors affecting this plant?

Soil, water, and energy from the Sun are some of the abiotic

factors that help control the growth of green plants

The Sun

Most life on Earth depends on energy from the Sun, an

important abiotic factor Green plants use energy from the

Sun to make food Other animals eat those green plants Still

other animals eat those animals Most organisms depend on

green plants The Sun’s energy also controls many other

abi-otic factors in the environment

Recall from Chapter 9 that areas of Earth receive different

amounts of radiation from the Sun because Earth’s surface is

curved Figure 2 shows how rays of sunlight hit Earth at a low

angle at the equator This causes the land areas along the

equator to be among the warmest places on Earth, and life is

abundant The poles are colder because the Sun’s rays hit

Earth at an angle, spreading the heat There are fewer

organ-isms at the poles due to the harsher climate

Why are the poles colder than areas near the equator?

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Figure 3 The

temper-ature of the water at the

surface of Earth’s oceans

ranges from 30°C near

the equator to 0°C at

the poles.

518 Chapter 12 • Ecological Roles

Temperature Without the Sun, Earth would be a frozen

wasteland The Sun’s energy warms Earth and makes it ble for humans and other organisms to survive The uneven warming of Earth’s surface from the Sun’s rays causes great temperature differences The Sun influences temperature, an abiotic factor in ecosystems Figure 3 shows the temperatures

possi-of Earth’s oceans

Temperature is one of the abiotic factors that affects plant growth Plants grow best in regions that are moderate—not too cold and not too hot Plants also grow well when the tem-perature does not change greatly This means that daily and seasonal temperatures are consistent Because there are more plants, regions with constant warm temperatures support the greatest numbers of living things Why do you think this is the case? Animal life is dependent on green plants More types of plants and animals can live in areas where the tem-peratures are consistent This explains why many more spe-cies live in tropical rain forests than in deserts or polar regions

Why are there more plants and animals in the tropics than the desert?

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Figure 4 Climate zones are based on long-term weather

patterns This map shows the average temperature for each

zone at the coldest time of year.

Identify which states contain the zone covering –6°C to –1°C?

Lesson 1 • Abiotic and Biotic Factors 519

Climate The Sun influences climate, another abiotic factor

When you need to decide what to wear each morning,

per-haps you start by checking the weather forecast In any area,

the weather can change from day to day Climate is the

pat-tern of weather that occurs in an area over many years You

learned in Chapter xx that climate does not change from day

to day, so you would not check a climate forecast to decide

whether to take your raincoat along when you head out for

the day Earth’s climate patterns are controlled by the

tem-perature differences between the equator and the poles

This difference creates winds and ocean currents that affect

climate

Scientists average temperature, precipitation, humidity, and

the number of days of sunshine to determine an area’s

cli-mate For example, Figure 4 shows zones of average

tempera-ture in the United States during the coldest time of the year

Farmers and gardeners use these zones to decide what kinds

of plants to grow in their part of the country

520 Chapter 12 • Ecological Roles

The Water Cycle Water is an important abiotic factor to

almost all life on Earth Water helps organisms absorb ents and is important in ridding organisms of wastes More organisms can survive in places with plenty of water

nutri-What happens if you hang damp laundry outside on a sunny day? Heat energy from the Sun evaporates water from the clothes Water also evaporates from rain-soaked high-ways, damp leaves in a forest, and the surfaces of lakes and oceans Water that evaporates enters the atmosphere

Figure 5 shows how water in the atmosphere condenses to form clouds Water falls from clouds back to Earth as rain, snow, sleet, or hail Some of this water flows over land into streams and rivers Some soaks into the ground Plants need this water to grow They take up water through their roots and release it from their leaves Animals play a part in the water cycle, too They drink water and excrete it as waste Extra water in the soil may drain downward and become groundwater

Figure 5 What happens to water that evaporates?

To explore more about the water cycle, visit ca6.msscience.com

Figure 6 Humus, the organic matter

in soil, helps plants to grow.

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Lesson 1 • Abiotic and Biotic Factors 521

Soil

Earlier you read how to grow a plant One

of the things you would need is a pot filled

with soil This abiotic factor might seem

sim-ple, but soils are not all the same For one

thing, they contain different minerals, such

as limestone or quartz These minerals affect

the chemistry of the soil, such as the acidity

or alkalinity Plants do not grow well if the

soil is too acidic or too alkaline Farmers and

gardeners also measure the concentrations of

important plant nutrients, including

nitro-gen, phosphorus, and potassium

Dead plants and animals decay in soil,

forming a dark-colored material that makes

nutrients available to plants, called humus

(HYEW mus) As you can see in Figure 6,

humus lies in a thin layer at the soil surface

As it slowly breaks down, the organic matter

in humus helps plants grow Humus also

sup-ports plant growth by holding water in the

soil Like a sponge, it soaks up water and

keeps the soil moist In nature, the regions

that support the most plant growth have soils

that are rich in humus

Explain how humus helps plants grow.

Air

Like the Sun, air is also an important

abi-otic factor Humans and many other

organ-isms can only survive in places where the air

contains enough oxygen Many organisms

use oxygen to help their cells release energy

Most organisms that use oxygen can only

survive for five minutes without it before

cells begin to die At higher elevations, the

mountain air contains less oxygen Mountain

climbers carry oxygen tanks to help them

breathe Some organisms can use less oxygen

than can others The air in a particular

eco-system determines the organisms that will

live there

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Figure 7 Oxygen and carbon dioxide flows between organisms.

522 Chapter 12 • Ecological Roles

Exchanging Gases Some organisms, like humans, take

oxy-gen from the air and release carbon dioxide Other organisms

do the opposite Plants and some other organisms take in carbon dioxide and give off oxygen Figure 7 shows the exchange of oxygen in the environment The grasses in this ecosystem take in carbon dioxide and release oxygen into the air The lion takes in this oxygen and releases carbon dioxide for the grasses to take in Green plants help keep these gases

in balance

Figure 7 Contrast the gases given off by plants and animals.

Air Pollution Some human activities can pollute the air Air

pollution is the contamination of the air by harmful stances Much of the pollution comes from vehicles and man-ufacturing Organisms can have difficulty surviving in contaminated air In humans, this can cause irritation in the respiratory system It can also cause more serious problems, such as certain types of cancer For wildlife, the pollution collects in the soil and water This affects the place where the organism lives It also affects the food supply What can you

sub-do to help reduce pollution? Small changes, such as turning off electrical appliances when not in use, are helpful Also, your family can walk, ride a bike, or take public transporta-tion instead of driving Of course, reducing the number of items you use, reuse items again, and recycle everyday items The fewer new items you use means less items have to be manufactured

S CIENCE U SE V C OMMON U SE

gas

Science Use a substance

hav-ing neither definite shape nor

volume that can expand

indefinitely You exhale carbon

Figure 8 Organisms of the same species together make

up a population.

Lesson 1 • Abiotic and Biotic Factors 523

Biotic Factors

Biotic factors are the living parts of an ecosystem Every

organism in an ecosystem depends on other organisms

Con-sider the coral reef ecosystem in Figure 8 Corals are tiny

marine animals Corals contain microscopic algae in their

tissues While the algae provide food and oxygen, the corals

provide a protected place for the algae to grow This close

interaction between two organisms is called symbiosis

Together, corals and algae build reef structures that provide

homes to many organisms Sea grasses and other plants

pro-vide shelter for fish looking for a place to hide from bigger

fish looking for something to eat

As in all types of ecosystems, plants and animals in coral

reefs compete with others for food or living space Some

ben-efit each other by providing food, a place to live, or a way to

hide from enemies A species is a group of organisms that

share similar characteristics and can reproduce among

them-selves producing fertile offspring Each species plays a

differ-ent role Together they are the biotic factors of the ecosystem

What are some biotic factors in a coral reef ecosystem?

Populations

How many people live in your town? The number of

indi-viduals of one species that occupy the same area is called a

population In ecosystems, the population of an organism

refers to all the individuals of that species that live in a given

location For example, a scientist might study the population

of condors in California or great white sharks in the Pacific

Ocean In a smaller ecosystem, a scientist could study the

population of frogs in a pond

WORD ORIGIN

population

from Latin populus; means

inhabitants

Figure 9 An ecosystem includes populations of organisms that inter- act with each other to form ecologi- cal communities.

Identify which abiotic factors affect this

community.

524 Chapter 12 • Ecological Roles

Communities

A community is all the populations of species that occupy

an area You can see in Figure 9 that a community includes more than one species In the Pacific Ocean, you would find different communities near the shore than in the deep sea Communities also change with distance from the equator Remember that temperature is one of the abiotic factors that affects living things As you go north or south from the equator, the temperature drops Different ecological commu-nities adapt to living in regions with different temperatures

Figure 10 shows how biotic factors can interact in a nian coastal scrub community

Califor-What makes up a community?

Limiting Factors

If you have ever kept a fish as a pet, you know there is a limit to how many fish you can add to the aquarium If you add too many fish to an aquarium, oxygen levels can drop too low, and the fish can die In nature, populations expand

until the biotic or abiotic factors become limiting A limiting

factor is an environmental factor that limits how large a

pop-ulation can grow If poppop-ulations get too large, competition for resources, such as food and water, will cause some individuals

Lesson 1 • Abiotic and Biotic Factors 525

Visualizing Biotic Factors

Figure 10

Hawks, snakes, and many other organisms make up

California’s coastal scrub community These

communi-ties have many shrubs and few trees They are

accus-tomed to hot, dry summers and mild, wet winters

During summer, many shrubs lose their leaves to

conserve water Animals living in this community

must adjust to great differences between summer

and winter water supplies.

Contributed by National Geographic

Rain Forest Desert

Figure 11 Ecosystems that support more plant growth provide food to a greater

number and variety of animals

Identify the limiting factors in each of these environments

526 Chapter 12 • Ecological Roles

Changing Factors

Limiting factors can change over time For example, in ecosystems that normally have plenty of rain, water can become a limiting factor during a drought Different factors limit different species Sun-loving plants do not grow well in the shade or in dense forests But mushrooms and forest wildflowers will grow well in the shade

At the beginning of this chapter, you learned what would

be needed to provide for a green plant to survive in your classroom What do humans need to survive? All organisms, including humans, need food, water, shelter, and space

Food

All organisms need food for energy In some ecosystems, there is plenty of food In others, food is scarce What do you think causes this difference? Recall how abiotic factors affect plant growth Temperature, types of soil, and amounts of sun-light and water are different from one ecosystem to another These abiotic factors affect plant growth The more plants that grow, the more food there is for other living things

Compare the abiotic and biotic factors of two ecosystems shown in Figure 11 Which looks like it would support more organisms? In a tropical rain forest, constant warmth and plentiful water create perfect conditions for many plant spe-cies The lush plant growth provides food to a variety of insects, birds, and other organisms In deserts, plant life is limited, so less food is available Less food means fewer organisms can live in deserts than in tropical rain forests

Figure 12 High in the mountains, water and other abiotic factors limit plant growth.

Treeline

Water

All living things need water, but some need more water

than others Organisms that live in sandy deserts are adapted

to a life that has little water during much of the year An

adaptation is any physical or behavioral characteristic that

allows an organism to be better suited to the environment

Cactus have waxy coverings to prevent water loss from

evapo-ration Another way organisms survive in deserts is by

stay-ing inactive durstay-ing the hot, dry summers Durstay-ing the brief

wet periods, wildflowers bloom, and animals gather food

before the dry weather forces them to become inactive again

Some animals have the ability to cool themselves

How do organisms survive in the desert?

Other than deserts, where else on Earth do you think water

could be a limiting factor? On snow-covered peaks, water

may stay frozen all year Even on peaks that do not stay

fro-zen, lack of water can limit plant growth If you drive or hike

up a mountain, you will notice the tall trees you will see in

the valley do not grow at higher elevations The higher you

go, the shorter the trees and bushes become Finally, you

reach an area like the one shown in Figure 12 At this high

elevation, no trees grow, and the vegetation is limited to

wild-flowers, grasses, lichens, and mosses What factors do you

think might cause these differences in plant communities

between the valley and the peak? One of the limiting factors

is water High in the mountains, the soils have a thin humus

layer They dry out quickly rather than remaining moist

between storms

ACADEMIC VOCABULARY

adapt (uh DAPT)

(verb) to make fit, often by

modification

Juan adapted quickly to his new school by making friends and joining the drama club.

Figure 13 In the oceans and on land, animals

seek shelter from their enemies.

Identify the places for shelter in these images.

528 Chapter 12 • Ecological Roles

Shelter

If you lived in the Arctic how would the design of your home be different from your home if you lived in a tropical region? Wherever you live, you want your home to keep you dry when it rains or snows You also might lock the doors for protection Similarly, organisms in all types of ecosystems need shelter from both abiotic and biotic factors

Animals living in harsh climates use shelter to protect themselves from abiotic factors In deserts and polar regions, for example, frogs dig burrows to avoid the heat or cold

As shown in Figure 13, shelter also protects organisms from their enemies How do you think fish in the Pacific Ocean escape from sharks? One way is by hiding behind a rock or a clump of seaweed On land, shrubs and piles of brush provide shelter for rabbits and mice, helping them to hide from eagles and owls

Why is shelter important?

Space

All organisms need space in which to live and grow In a garden or a forest, plants will grow best if they do not have to compete with other plants Animals also need space Some animals defend their territories in order to protect enough land to meet their needs for food, water, and shelter