1 FOCUSObjectives4.1.1 Identify the causes of climate.4.1.2 Explain how Earth’s tempera-

ture range is maintained.4.1.3 Identify Earth’s three main cli-

mate zones.

Vocabulary PreviewReview the term latitude by asking stu-dents to describe what the term refersto. (The distance north and south of theequator) Display a large world map orglobe, and have a volunteer point outthe latitude lines on it.

Reading StrategyPair students who are not strongreaders with proficient readers whocan help them select main ideas,subtopics, and relevant details for theoutline.

2 INSTRUCT

What Is Climate?Use Community ResourcesEncourage students to interviewolder family members and friends tofind out what the climate was like intheir area 25, 50, or more years ago.Instruct students to take notes duringthe interview. In class, let studentscompare notes to see whether thepeople they interviewed agree aboutclimate changes in their lifetimes.

The GreenhouseEffectMake ConnectionsPhysics Ask: In what forms doesEarth receive solar energy? (As lightand other forms of radiation) Besidesradiation, how is heat transferred?(By conduction [transfer from moleculeto molecule within or between objects]and by convection [transfer in currents ofa fluid, such as air]) What causes thegreenhouse effect? (Earth’s atmos-phere traps much of the energy from thesun, raising the temperature of theatmosphere.)

Ecosystems and Communities 87

4–1 The Role of Climate

If you live in Michigan, you know you cannot grow bananatrees in your backyard. Bananas are tropical plants that need

plenty of water and heat. They won’t survive in freezing temper-atures. It may not be as obvious that cranberries won’t grow inthe Rio Grande Valley of Texas. Cranberries need plenty ofwater and a cold rest period. They cannot tolerate the months ofvery hot weather that often occur in the Rio Grande Valley.

Bananas and cranberries, like other plants and animals,vary in their adaptations to temperature, rainfall, and otherenvironmental conditions. Species also vary in their tolerancesfor conditions outside their normal ranges. That’s why climate isimportant in shaping ecosystems—and why understandingclimate is important in ecology.

What Is Climate?In the atmosphere, temperature, precipitation, and other envi-ronmental factors combine to produce weather and climate.

is the day-to-day condition of Earth’s atmosphere at aparticular time and place. The weather where you live may beclear and sunny one day but cloudy and cold the next.on the other hand, refers to the average, year-after-year condi-tions of temperature and precipitation in a particular region.

Climate is caused by the interplay of many factors, includingthe trapping of heat by the atmosphere, the latitude, the trans-port of heat by winds and ocean currents, and the amount ofprecipitation that results. The shape and elevation of land-masses also contribute to global climate patterns.

The energy of incoming sunlight drives Earth’s weather andhelps determine climate. As you might expect, solar energy hasan important effect on the temperature of the atmosphere. Atthe same time, the presence of certain gases in the atmospherealso has an effect on its temperature.

The Greenhouse EffectTemperatures on Earth remain within a range suitable for lifebecause the biosphere has a natural insulating blanket—theatmosphere. Carbon dioxide, methane, water vapor,and a few other atmospheric gases trap heat energy andmaintain Earth’s temperature range. These gases functionlike the glass windows of a greenhouse. Just as the glass keepsthe greenhouse plants warm, these gases trap the heat energyof sunlight inside Earth’s atmosphere. The natural situation inwhich heat is retained by this layer of greenhouse gases iscalled the shown in Figure 4–1.greenhouse effect,

Climate,

Weather

Key Concepts• How does the greenhouse

effect maintain the biosphere’stemperature range?

• What are Earth’s three mainclimate zones?

Vocabularyweather • climategreenhouse effect • polar zonetemperate zone • tropical zone

Reading Strategy: Outlining Before you read,use the headings in this sectionto make an outline aboutclimate. As you read, fill in thesubtopics and smaller topics.Then, add phrases or a sentenceafter each subtopic to providekey information.

� Figure 4–1 Carbondioxide, water vapor, and severalother gases in the atmosphereallow solar radiation to enter thebiosphere but slow down the lossof heat to space. These green-house gases cause the greenhouseeffect, which helps maintain Earth’stemperature range.

Green-house gases trapsome heat

Atmosphere

Sunlight

Some heat escapes into space

Earth’s surface

SECTION RESOURCES

Print:

• Teaching Resources, Section Review 4–1• Reading and Study Workbook A,

Section 4–1• Adapted Reading and Study Workbook B,

Section 4–1• Biotechnology Manual, Concept 8• Lesson Plans, Section 4–1

Technology:

• iText, Section 4–1• Transparencies Plus, Section 4–1• Virtual Labs CD-ROM, The Effect of

Temperature on Dissolved Oxygen

Tim

eSaver

Section 4–1

88 Chapter 4

Greenhouse gases allow solar energy to penetrate the atmos-phere in the form of sunlight. Much of the sunlight that hits thesurface of our planet is converted into heat energy and thenradiated back into the atmosphere. However, those same gases donot allow heat energy to pass out of the atmosphere as readily aslight energy enters it. Instead, the gases trap heat inside Earth’satmosphere. If these gases were not present in the atmosphere,Earth would be 30 degrees Celsius cooler than it is today.

The Effect of Latitude on ClimateBecause Earth is a sphere that is tilted on its axis, solar radiationstrikes different parts of Earth’s surface at an angle that variesthroughout the year. At the equator, the sun is almost directlyoverhead at noon all year. At the North and South poles, however,the sun is much lower in the sky for months at a time. Look atFigure 4–2, and you will see that differences in the angle of sun-light directed at different latitudes result in the delivery of moreheat to the equator than to the poles. The difference in heat distri-bution with latitude has important effects on Earth’s climate zones.

As a result of differences in latitude and thusthe angle of heating, Earth has three main climatezones: polar, temperate, and tropical. The are cold areas where the sun’s rays strike Earth at a very lowangle. These zones are located in the areas around the Northand South poles, between 66.5° and 90° North and Southlatitudes. The sit between the polar zonesand the tropics. Because temperate zones are more affected bythe changing angle of the sun over the course of a year, theclimate in these zones ranges from hot to cold, depending onthe season. The or tropics, is near the equa-tor, between 23.5° North and 23.5° South latitudes. Thetropics thus receive direct or nearly direct sunlight year-round, making the climate almost always warm. Figure 4–2shows Earth’s main climate zones.

What effect does latitude have on climate?

tropical zone,

temperate zones

polar zones

Most direct sunlight

Sunlight

Sunlight

SunlightSunlight

Sunlight

Antarctic Circle

66.5°N

66.5°S

23.5°N

0°

23.5°S

Tropic of Cancer

Tropic of Capricorn

Equator

Arctic Circle

90°N North Pole

90°S South Pole

Polar

Temperate

Tropical

Temperate

Polar

� Figure 4–2 Earthhas three main climatezones. These climate zonesare caused by the unequalheating of Earth’s surface.Near the equator, energyfrom the sun strikes Earthalmost directly. Near thepoles, the sun’s rays strikeEarth’s surface at a lowerangle. The same amount ofsolar energy is spread outover a larger area, heatingthe surface less than at theequator.

For: Links on climate and the greenhouse effect

Visit: www.SciLinks.orgWeb Code: cbn-2041

NSTA

4–1 (continued)

Inclusion/Special NeedsTo help students who have difficulty graspingthe information in the subsection Heat Transportin the Biosphere, read aloud the sentence aboutwhy winds form—warm air tends to rise andcool air tends to sink. This concept is commonsense for most students, and once they under-stand that this phenomenon causes winds andocean currents, they will be better able tounderstand how heat moves throughout theoceans and the atmosphere.

Advanced LearnersPoint out to students who need an extra chal-lenge that the word tropics derives from a Latinword for “solstice.” Challenge these students todetermine the connection between the solsticesand the tropics of Cancer and Capricorn. Havethem make a presentation of their findings tothe class, complete with visual aids.

The Effect of Latitudeon ClimateUse VisualsFigure 4–2 After students have stud-ied the figure and read the caption,ask: Why does solar radiation strikedifferent parts of Earth at an anglethat varies throughout the year?(Earth is a sphere that is tilted on itsaxis.) What are the names given tothe latitude lines of 23.5ºN and23.5ºS? (The Tropic of Cancer and theTropic of Capricorn, respectively) Whatclimate zone is between the Tropicof Cancer and the Tropic ofCapricorn? (The tropical zone) Whichclimate zone contains the UnitedStates? (The northern temperate zone)Why does the climate of a regionin a temperate zone have a rela-tively wide range of temperatures,depending on the season? (Thetemperate zones are more affected bythe changing angle of the sun over thecourse of a year.)

Heat Transport in theBiosphereBuild Science SkillsUsing Models To reinforce stu-dents’ understanding of how Earth’srotation affects currents and winds,give each pair of students a paperplate. Have one student hold a fin-ger on the center of the platewhile slowly turning the plate with the other hand. The secondstudent should put the point of a pencil near the center of the plate and draw a line straight to the plate’s edge. Students will seethat the line drawn on the plate isnot straight but curved, due to theplate’s rotation. Explain that Earth’srotation has the same effect on winds and currents.

NSTA

Download a worksheet on climate and the greenhouseeffect for students to complete, andfind additional teacher supportfrom NSTA SciLinks.

3 ASSESSEvaluate UnderstandingCall on students at random to identi-fy the major climate factors discussedin this section and explain how eachfactor helps determine climate.

ReteachStart a simple diagram of the green-house effect by drawing a curvingsection of Earth’s surface on theboard. Then, have different studentsin turn add features and labels to thedrawing to explain the greenhouseeffect step by step.

Ecosystems and Communities 89

Heat Transport in the BiosphereThe unequal heating of Earth’s surfacedrives winds and ocean currents, whichtransport heat throughout the biosphere.Winds form because warm air tends to riseand cool air tends to sink. Consequently, airthat is heated near the equator rises. Atthe same time, cooler air over the polessinks toward the ground. The upwardmovement of warm air and the downwardmovement of cool air create air currents, orwinds, that move heat throughout theatmosphere, from regions of sinking air toregions of rising air. The prevailing winds,shown in Figure 4–3, bring warm or coldair to a region, affecting its climate.

Similar patterns of heating and coolingoccur in Earth’s oceans. Cold water near thepoles sinks and then flows parallel to theocean bottom, eventually rising again inwarmer regions through a process calledupwelling. Meanwhile, surface water ismoved by winds. In both cases, the water flowcreates ocean currents. Like air currents,ocean currents transport heat energy within the biosphere. Surfaceocean currents warm or cool the air above them, thus affecting theweather and climate of nearby landmasses.

Continents and other landmasses can also affect winds andocean currents. Landmasses can interfere with the movement ofair masses. For example, a mountain range causes a moist airmass to rise. As this happens, the air mass cools and moisturecondenses, forming clouds that bring precipitation to the moun-tains. Once the air mass reaches the far side of the mountains, ithas lost much of its moisture. The result is a rain shadow—anarea with a dry climate—on the far side of the mountains.

� Figure 4–3 Earth’s winds (top)and ocean currents (bottom)interact to help produce Earth’sclimates. The curved paths of somecurrents and winds are the result ofEarth’s rotation. InterpretingGraphics In what direction do coldcurrents in Earth’s oceans generallymove?

23.5°N

23.5°S

66.5°NPolar Easterlies

Polar Easterlies

Westerlies

Westerlies

Northeast Trade Winds

Southeast Trade Winds

66.5°S

0°

WINDS

Equator

Prevailingwinds

23.5°N

23.5°S

66.5°N

66.5°S

0°

OCEAN CURRENTS

Equator

Warm currents

Cold currents

1. Key Concept What is thegreenhouse effect?

2. Key Concept DescribeEarth’s three main climate zones.

3. What are the main factors thatdetermine Earth’s climate?

4. Describe two ways in which heatis transported in the biosphere.

5. Critical Thinking ApplyingConcepts A biologist recordedthe bird species in her region.Then, she spotted a bird that wasnot supposed to live in theregion. How might variationsrelate to this occurrence?

4–1 Section AssessmentModelingEarth rotates daily on its axisand is tilted at an angle of23.5° in relation to the sun.Using a flashlight to representthe sun and a globe to represent Earth, demonstratedifferent levels of light inEarth’s three climate zones.

Answers to . . . Regions at higher lati-

tudes receive less heat energy per unitarea than do regions near the equator.As a result, the temperate and polarzones have cooler climates than thetropical zone.

Figure 4–3 Cold currents generallymove in curving paths toward theequator.

If your class subscribes to theiText, use it to review the KeyConcepts in Section 4–1.

4–1 Section Assessment1. Gases trap heat inside Earth’s atmosphere.2. Tropical zone: near equator; receives direct or

nearly direct sunlight year-round, climate isalmost always warm. Polar zones: near Northand South poles; receive the sun’s rays at alow angle, climate is cold. Temperate zones:between the other two zones; receive sun-light at changing angles during the year,climate ranges from hot to cold.

3. Trapping of heat by the atmosphere, latitude,transport of heat by winds and ocean cur-rents, amount of precipitation

4. Winds and ocean currents5. Animal species show variations in their toler-

ances for different climatic conditions. Thebird was probably just a bit beyond its usualrange. Because the species varies in its toler-ance, it could survive beyond its range.

Demonstrate how to hold theglobe in a way that models theangle that Earth tilts on its axis,23.5º. Have students note that ifthe North Pole is tilted away fromthe light, then the setup modelsthe positions of sun and Earth dur-ing winter in the United States. Ifthe North Pole is tilted toward thesun, then the setup models thepositions during summer in theUnited States. Make sure studentsfind these latitudes on the globe:66.5º North and South, 90º Northand South, 23.5º North andSouth, and the equator. Have stu-dents work in pairs or smallgroups.

90 Chapter 4

1 FOCUSObjectives4.2.1 Explain how biotic and abiotic

factors influence an ecosystem.4.2.2 Identify the interactions that

occur within communities.4.2.3 Describe how ecosystems

recover from a disturbance.

Vocabulary PreviewThe text provides pronunciations for most of the new Vocabulary termsin this section. Encourage students to use a dictionary to look up thephonetic spellings of the words forwhich pronunciations are not given,convert those spellings to the systemused in this text, and include thephonetic spellings when they list thehighlighted, boldface terms.

Reading StrategyStudents often confuse the terms sym-biosis, mutualism, and commensalism.To help them understand and remem-ber the distinctions, have them lookup the derivations of the words in adictionary and note the derivationswhen they list the highlighted, bold-face terms.

2 INSTRUCT

Biotic and Abiotic FactorsBuild Science SkillsApplying Concepts Point out tostudents that in any ecosystem,removing biotic elements can dra-matically affect the ecosystem’sabiotic conditions. For example, thetrees in a forest hold topsoil withtheir roots, shade the soil, contributeorganic matter to the soil in the formof dead leaves, and return water tothe atmosphere through evaporationand transpiration. Removing treesfrom the forest ecosystem reducesthese benefits. Ask students to sug-gest other examples of removingbiotic elements from an ecosystem.

If you ask an ecologist where a particular organism lives, thatperson might say the organism lives on a Caribbean coral

reef, or in an Amazon rain forest, or in a desert in the AmericanSouthwest. Those answers provide a kind of ecological addressnot unlike a street address in a city or town. An ecologicaladdress, however, tells you more than where an organism lives.It tells you about the climate the organism experiences andwhat neighbors it is likely to have. But what shapes the ecosys-tem in which an organism lives?

Biotic and Abiotic FactorsEcosystems are influenced by a combination of biological andphysical factors. The biological influences on organisms withinan ecosystem are called These include theentire living cast of characters with which an organism mightinteract, including birds, trees, mushrooms, and bacteria—inother words, the ecological community. Biotic factors that influ-ence a bullfrog, for example, might include the tiny plants andalgae it eats as a tadpole, the herons that eat the adult frog, andother species that compete with the bullfrog for food or space.

Physical, or nonliving, factors that shape ecosystems arecalled (ay-by-AHT-ik) For example, the climateof an area includes abiotic factors such as temperature, precipi-tation, and humidity. Other abiotic factors are wind, nutrientavailability, soil type, and sunlight. For example, the bullfrog inFigure 4–4 is affected by abiotic factors such as the availability ofwater and the temperature of the air. Together, biotic andabiotic factors determine the survival and growth of anorganism and the productivity of the ecosystem in whichthe organism lives. The area where an organism lives is calledits A habitat includes both biotic and abiotic factors.

Give an example of an abiotic factor.

habitat.

factors.abiotic

biotic factors.

4–2 What Shapes an Ecosystem?

Key Concepts• How do biotic and abiotic

factors influence an ecosystem?

• What interactions occur withincommunities?

• What is ecological succession?

Vocabularybiotic factorabiotic factorhabitatnicheresourcecompetitive exclusion principlepredationsymbiosismutualismcommensalismparasitismecological successionprimary successionpioneer speciessecondary succession

Reading Strategy: Building Vocabulary Beforeyou read, preview new vocabu-lary terms by skimming thesection and making a list of thehighlighted, boldface terms.Leave space to make notes asyou read.

� Figure 4–4 Like allecosystems, this pond is shapedby a combination of biotic andabiotic factors. The bullfrog,plants, and other organisms in thepond are biotic factors. The water,the air, and the rock on which thebullfrog sits are abiotic factors.

SECTION RESOURCES

Print:

• Laboratory Manual A, Chapter 4 Lab• Laboratory Manual B, Chapter 4 Lab• Teaching Resources, Section Review 4–2,

Enrichment, Chapter 4 Exploration• Reading and Study Workbook A, Section 4–2• Adapted Reading and Study Workbook B,

Section 4–2• Lesson Plans, Section 4–2

Technology:

• iText, Section 4–2• Transparencies Plus, Section 4–2

Tim

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Section 4–2

The NicheAddress MisconceptionsStudents sometimes misunderstandwhat a niche is, believing it to be apart of an ecosystem. Use simpleanalogies to clarify the meaning ofthe term. For example, each playeron a baseball team has a specificniche—a different role to play.

Ecosystems and Communities 91

The NicheIf an organism’s habitat is its address, its niche is its occupa-tion. A (NITCH) is the full range of physical and biologi-cal conditions in which an organism lives and the way in whichthe organism uses those conditions. For instance, part of thedescription of an organism’s niche includes its place in the foodweb. Another part of the description might include the range oftemperatures that the organism needs to survive. The combina-tion of biotic and abiotic factors in an ecosystem often deter-mines the number of different niches in that ecosystem.

A niche includes the type of food the organism eats, how itobtains this food, and which other species use the organism asfood. For example, a mature bullfrog catches insects, worms,spiders, small fish, or even mice. Predators such as herons,raccoons, and snakes prey on bullfrogs.

The physical conditions that the bullfrog requires to surviveare part of its niche. Bullfrogs spend their lives in or near thewater of ponds, lakes, and slow-moving streams. A bullfrog’sbody temperature varies with that of the surrounding water andair. As winter approaches, bullfrogs burrow into the mud of pondor stream bottoms to hibernate.

The bullfrog’s niche also includes when and how it repro-duces. Female bullfrogs lay their eggs in water during thewarmer months of the year. The young frogs, called tadpoles,live in the water until their legs and lungs develop.

niche

How do abiotic factors affectdifferent plant species?

Materials presoaked rye and rice seeds, sand,potting soil, 4 paper cups

Procedure

1. Use a pencil to punch three holes in the bottom ofeach cup. Fill 2 cups with equal amounts of sandand 2 cups with the same amount of potting soil.

2. Plant 5 rice seeds in one sand-filled cup and 5 riceseeds in one soil-filled cup. Plant 5 rye seeds ineach of the other 2 cups. Label each cup with thetype of seeds and soil it contains.

3. Place all the cups in a warm, sunny location. Eachday for 2 weeks, water the cups equally and recordyour observations of any plant growth. CAUTION:Wash your hands well with soap and warm waterafter handling plants or soil.

Analyze and Conclude1. Analyzing Data In which medium did the rice

grow best—sand or soil? Which was the bettermedium for the growth of rye?

2. Inferring Soil retains more water than sand,providing a moister environment. What can youinfer from your observations about the kind ofenvironment that favors the growth of rice? Thegrowth of rye?

3. Drawing Conclusions Which would competemore successfully in a dry environment—rye orrice? In a moist environment?

Answer to . . . The example should be

any nonliving factor, such as air, water,soil, or rocks.

Less Proficient ReadersSome students learn best when material isorganized. Help these students better under-stand succession in a marine ecosystem byhaving them create a flowchart of the processdiscussed on pages 96 and 97. You could havestudents work in small groups to make thesegraphic organizers. When groups finish, displaythe flowcharts so that groups can compare theirapproaches.

Advanced LearnersEncourage students who need an extra chal-lenge to research the various types of defensesthat have evolved in prey species as protectionagainst predators. Such defenses include cam-ouflage, mechanical defenses such as quills andthorns, chemical defenses such as toxins, warn-ing coloration, and mimicry. Have studentsshare their findings with the class in oral reports,posters, or displays.

Objective Students will be able todescribe how abiotic factors affectgrowth in different species ofplants.Skill Focus Drawing ConclusionsMaterials rye and rice seeds, sand,potting soil, 4 paper cupsTime 15 minutes for setup; briefobservation and recording each dayfor 2 weeksAdvance Prep Soak the rice andrye seeds in water overnight.Strategies• Have students place the cups in

trays or other shallow containersto hold any water, sand, and soilthat may leak from the holes.

• Emphasize that except for the typeof soil and type of seeds in eachcup, all variables must be kept thesame for all four cups.

Alternative Materials If rye isnot available, you may use wheatseeds instead.Expected Outcome Rice seeds willnot grow well in the sand-filled cupbecause the water drains out andleaves the sand too dry. Rye seedsshould grow well in soil or sand.Analyze and Conclude1. Both types of seeds will be moresuccessful in soil. However, the effecton rice will be more pronounced.2. Rice requires a moister environ-ment than rye does. Rye cantolerate dry conditions better thanrice can but also benefits from anample supply of water.3. Rye will be more successful thanrice in dry conditions. Rice will bemore successful than rye in moistconditions.

92 Chapter 4

CommunityInteractionsDemonstrationMark off a 3-meter-square area withmasking tape or string. Scatter 25uncolored toothpicks (or other smallobjects) and 25 colored toothpicksover the area. Explain that the tooth-picks represent two different speciesof insects. Choose two students torepresent different species of lizardsthat eat both types of insects. At asignal from you, the two lizards startcatching insects of both types. Signalthe lizards to stop after 5–10 sec-onds, and ask them to count theirinsects. Rescatter the toothpicks andrepeat the activity, but this time haveone lizard eat only uncolored insectsand the other lizard eat only coloredinsects. Compare the insect countsfrom the two different methods. Askthe “lizards”: Was it easier to catchinsects when you were competingwith each other or when you eachhad a different food? (When eachhad a different food) Also ask theother students to describe competi-tive behaviors they observed.

Build Science SkillsProblem Solving Emphasize thatany given ecosystem has only a cer-tain amount of space, food, water,and other life essentials. Ask: If oneorganism is involved in direct com-petition for life essentials, what arethe possible outcomes for thatorganism? (The organism may winthe struggle and survive, or it may losethe struggle and die.) Is there anyother alternative for organismsthat are in competition with otherorganisms? (If the competition isbetween different yet similar species,the organisms may change in waysthat will decrease competition. In thisway, both species may survive.)

As you will see, no two species can share the same niche inthe same habitat. However, different species can occupy nichesthat are very similar. For instance, the three species of NorthAmerican warblers shown in Figure 4–5 live in the same sprucetrees but feed at different elevations and in different parts ofthose trees. The species are similar, yet each warbler has adifferent niche within the forest.

What is a niche?

Community Interactions When organisms live together in ecological communities, theyinteract constantly. These interactions help shape the ecosystemin which they live. Community interactions, such ascompetition, predation, and various forms of symbiosis,can powerfully affect an ecosystem.

Competition Competition occurs when organisms of thesame or different species attempt to use an ecological resourcein the same place at the same time. The term refersto any necessity of life, such as water, nutrients, light, food, orspace. In a forest, for example, broad-leaved trees such as oak orhickory may compete for sunlight by growing tall, spreading outtheir leaves, and blocking the sunlight from shorter trees.Similarly, two species of lizards in a desert might compete byattempting to eat the same type of insect.

Direct competition in nature often results in a winner and aloser—with the losing organism failing to survive. A fundamen-tal rule in ecology, the states that no two species can occupy the same niche in thesame habitat at the same time. Look again at the distribution ofthe warblers in Figure 4–5. Can you see how this distributionavoids direct competition among the different warbler species?

competitive exclusion principle,

resource

Fee

ding

hei

ght (

met

ers)

18

12

6

0Spruce tree

Bay-Breasted WarblerFeeds in the middle

part of the tree

Yellow-Rumped WarblerFeeds in the lower part of the tree andat the bases of the middle branches

Cape May WarblerFeeds at the tips of branchesnear the top of the tree

� Figure 4–5 Each of thesewarbler species has a different nichein its spruce tree habitat. By feedingin different areas of the tree, thebirds avoid competing with oneanother for food. Inferring Whatwould happen if two of the warblerspecies attempted to occupy thesame niche?

The competitive exclusion principleThe competitive exclusion principle was first pos-tulated by Russian ecologist G. F. Gause in 1934.In laboratory experiments, Gause studied theeffect of interspecific competition on two closelyrelated species of protists. When he cultured thetwo species separately, both populations grewrapidly and then leveled off at the culture’s

carrying capacity. When he cultured the twospecies together, however, one species apparentlyhad a competitive edge in obtaining food, andthe other species was driven to extinction in theculture. Gause concluded that two species so similar that they compete for the same limitedresources cannot coexist in the same place. Hisconclusion was later confirmed by further studies.

HISTORY OF SCIENCE

4–2 (continued)

Build Science SkillsProblem Solving Explain thatunder normal conditions, prey popu-lations seldom become extinct as aresult of predation. Tell students toimagine an ecosystem in which apredator species has killed off anentire prey species. Ask: What wouldthe possible consequences be forthe predators? (They would run outof food and die, they would have tochange their eating habits and findother prey, or they would have to moveto another area where that preyspecies still survives.)

Build Science SkillsApplying Concepts Have each stu-dent list examples of symbioticrelationships that he or she knowsfrom previous learning or hasresearched. In a class discussion, askvolunteers to describe exampleswithout identifying the type of sym-biosis each example represents. Aftereach description, challenge other stu-dents to identify the relationship asmutualism, commensalism, or para-sitism.

Ecosystems and Communities 93

Predation An interaction in which one organismcaptures and feeds on another organism is called

(pree-DAY-shun). The organism that doesthe killing and eating is called the predator (PRED-uh-tur), and the food organism is the prey. Cheetahsare active predators with claws and sharp teeth. Theirpowerful legs enable them to run after prey. Otherpredators, such as anglerfishes, are more passive. Ananglerfish has a fleshy appendage that resembles afishing lure, which it uses to draw unsuspecting preyclose to its mouth.

Symbiosis Any relationship in which two specieslive closely together is called (sim-by-OH-sis), which means “living together.” Biologists recog-nize three main classes of symbiotic relationships innature: mutualism, commensalism, and parasitism.Examples of these three symbiotic relationships areshown in Figure 4–6.

Mutualism In (MYOO-choo-ul-iz-um),both species benefit from the relationship. Many flow-ers, for example, depend on certain species of insectsto pollinate them. The flowers provide the insects withfood in the form of nectar, pollen, or other substances,and the insects help the flowers reproduce.

Commensalism In (kuh-MEN-sul-iz-um), one member of the association benefitsand the other is neither helped nor harmed. Smallmarine animals called barnacles, for example, oftenattach themselves to a whale’s skin. The barnaclesperform no known service to the whale, nor do theyharm it. Yet, the barnacles benefit from the constantmovement of water past the swimming whale,because the water carries food particles to them.

Parasitism In (PAR-uh-sit-iz-um),one organism lives on or inside another organism andharms it. The parasite obtains all or part of its nutri-tional needs from the other organism, called the host.Generally, parasites weaken but do not kill their host,which is usually larger than the parasite. Tapeworms,for example, are parasites that live in the intestinesof mammals. Fleas, ticks, and lice live on the bodies ofmammals, feeding on the blood and skin of the host.

parasitism

commensalism

mutualism

symbiosis

predation

Figure 4–6 Three examples of symbiosis are shown: mutualism,commensalism, and parasitism. Predicting What would happen to the aphids if the ant died?

Mutualism The ant cares for the aphids andprotects them from predators. The aphidsproduce a sweet liquid that the ant drinks.

Commensalism The orchid benefits from itsperch in the tree as it absorbs water and miner-als from rainwater and runoff, but the tree is notaffected.

Parasitism A tick feeds on the blood of its hostand may also carry disease-causing microorganisms.

Answers to . . . The full range of physical

and biological conditions in which anorganism lives and the way in whichthe organism uses those conditions

Figure 4–5 Most likely, one warblerspecies would be more successful inthat niche, and the other species wouldnot survive.

Figure 4–6 Without the ants, theaphids could be eaten by predators.

Predation and diversityIn nature, predator species rarely kill and eat alltheir prey species, which would reduce commu-nity diversity. In fact, studies have shown thatpredation can actually help maintain diversity.One example of this process involves the graywolf, a top predator in its ecosystem. Wherewolves were hunted to extinction, such as inmany parts of North America, populations of

deer and other herbivores increased dramatically.As these populations overgrazed the vegetation,many plant species that could not tolerate suchgrazing pressure disappeared from the ecosys-tem. In turn, many insects and small animals thatdepended on the plants for food also disap-peared. The elimination of wolves thus producedan ecosystem with considerably less speciesdiversity.

BACKGROUND

94 Chapter 4

Ecological SuccessionDemonstrationThe following activity models stagesof succession described on this page.Elicit student volunteers to help youcreate the model. Put a 2.5-cm layerof gravel in the bottom of a dishpan,and cover with a 10-cm layer of soil.Make a pond by sinking a shallowdish into the soil so its top is evenwith the soil surface. Put a 1-cm layerof soil in the bottom of the pond.Slowly pour water into the dishpanuntil the pond is completely full andthe soil around it is wet. Sprinkle ahandful of grass seeds over the entiredishpan. Leave the dishpan near asunny window. Every 3 to 4 days,sprinkle grass seeds over the dishpanagain. Lightly water the soil to keep itdamp, but do not refill the pond orclean it out. Over time, the pond willbecome shallower and will eventuallyfill in with growing grass. When thishas occurred, sprinkle a handful ofmixed birdseed over the dishpanonce a week for two weeks. The bird-seed plants, which will be larger thanthe grass plants, represent the grad-ual invasion of shrubs and trees andthe succession from a meadow to aforest.

Build Science SkillsProblem Solving Ask: What typesof human activities can disturb anecosystem and cause succession?(Examples include logging, strip mining,draining a marsh, clearing woodland togrow crops or graze livestock, removinga beaver dam, and the like.)

2 31 4

Ecological SuccessionOn the time scale of a human life, some ecosystems may seemstable. The appearance of stability is often misleading, becauseecosystems and communities are always changing. Sometimes,an ecosystem changes in response to an abrupt disturbance,such as a severe storm. At other times, change occurs as a moregradual response to natural fluctuations in the environment.

Ecosystems are constantly changing in response tonatural and human disturbances. As an ecosystemchanges, older inhabitants gradually die out and neworganisms move in, causing further changes in the com-munity. This series of predictable changes that occurs in acommunity over time is called Some-times succession results from slow changes in the physicalenvironment. A sudden natural disturbance from human activi-ties, such as clearing a forest, may also be a cause of succession.

Primary Succession On land, succession that occurs onsurfaces where no soil exists is called For example, primary succession occurs on the surfaces formedas volcanic eruptions build new islands or cover the land withlava rock or volcanic ash. Primary succession also occurs onbare rock exposed when glaciers melt.

In Figure 4–7, you can follow the stages of primary succes-sion after a volcanic eruption. When primary succession begins,there is no soil, just ash and rock. The first species to populatethe area are called The pioneer species onvolcanic rocks are often lichens (LY-kunz). A lichen is made up ofa fungus and an alga and can grow on bare rock. As lichensgrow, they help break up the rocks. When they die, the lichensadd organic material to help form soil in which plants can grow.

What are pioneer species?

pioneer species.

primary succession.

ecological succession.

� Figure 4–7 Primary successionoccurs on newly exposed surfaces,such as this newly deposited volcanicrock and ash. (1) A volcanic eruptiondestroys the previous ecosystem. (2) The first organisms to appear arelichens. (3) Mosses soon appear, andgrasses take root in the thin layer ofsoil. (4) Eventually, tree seedlings andshrubs sprout among the plantcommunity. Predicting What typesof animals would you expect to appearat each stage, and why?

Succession and chanceMany ecologists once believed that successionwas an orderly and predictable process. Today,they realize that random, unpredictable eventsmay influence which species succeed and whichdie off after a disturbance. For example, randomvariables such as the season of year the distur-bance occurs, the wind direction and rainfallimmediately after the disturbance, and which

organisms are in an active stage of their breedingcycle can change the succession of a communityafter a fire, volcanic eruption, or other major dis-turbance. Ecologists have also found that climaxcommunities are often not as stable as they wereonce thought to be. In studying coral reefs andtropical rain forests, for example, researchers findshifting patchworks of early, middle, and late suc-cessionary communities.

BIOLOGY UPDATE

4–2 (continued)

Use Community ResourcesInvite students to cite examples ofnatural or human disturbances theyhave seen in their area. Emphasizethat the disturbance need not be alarge-scale event, such as cuttingdown all the trees in an area ofwoodland, but could be on a smallscale—for example, homeownersremoving thorny bushes from a nar-row strip of land between theirhouses. Ask students to describe anychanges they observed after the dis-turbance or, if the disturbance is veryrecent, to predict changes they thinkwill occur over time. Take the class toa disturbed site, if feasible, or ask stu-dents to visit a site on their ownperiodically to observe changes thatoccur during the school year.

Ecosystems and Communities 95

Secondary Succession Components of an ecosys-tem can be changed by natural events, such as fires,or by human activities, such as farming. Thesechanges may affect the ecosystem in predictable orunpredictable ways. When the disturbance is over,community interactions tend to restore the ecosys-tem to its original condition through

For example, secondary successionoccurs after wildfires burn woodlands and when landcleared for farming is abandoned. Figure 4–8 showstrees regrowing after a wildfire. In fact, fires set bylightning occur in many ecosystems, and some plantsare so adapted to periodic fires that their seeds won’tsprout unless exposed to fire!

Ecologists used to think that succession in agiven area always proceeded through predictablestages to produce the same stable “climax commu-nity.” Old-growth forests in the Pacific Northwest, forexample, were considered climax communities. Butnatural disasters, climate change, and human activ-ity such as introduction of nonnative species pro-foundly affect these communities today. Healthyecosystems usually recover from natural distur-bances because of the way components of the systeminteract. Ecosystems may or may not recover fromlong-term, human-caused disturbances.

succession.secondary

� Figure 4–8 Ten years after wildfires burnedregions of Yellowstone National Park, small evergreentrees have begun to regenerate the forest. PredictingHow do you think this region will look 20 years after thefires?

Forestry TechnicianJob Description: work outdoors to helpmaintain, protect, and develop forests (byplanting trees, fighting insects and diseasesthat attack trees, and controlling soil erosion)

Education: two- or four-year college degree inforestry, wildlife, or conservation; summerwork in parks, state and national forests; andprivate industry provides on-the-job training

Skills: knowledge of the outdoors and basicsafety precautions; communication skills forworking with the public; keen observationalskills; physical fitness for jobs that requirewalking long distances through forests

Highlights: help to manage and conserveforest biomes by analyzing data, planting trees,and managing fires when necessary; contributeto people’s enjoyment of outdoor recreation

Careers in Biology

For: Career linksVisit: PHSchool.comWeb Code: cbb-2042

To help students understand ecological succes-sion, have them interview an older familymember or neighbor who has lived in theirneighborhood for a long time. Ask the person todescribe how the neighborhood has changedover time. Make sure that students ask the fol-lowing questions. (1) Have areas that wereformerly grassy been paved or developed?

(2) Have any farms, parks, or lots returned totheir wild state? Ask students to write a summaryof their interview and then share it with the class.

—Deidre GalvinBiology TeacherRidgewood High SchoolRidgewood, NJ

TEACHER TO TEACHER

Encourage students to use libraryresources to find out how to getstarted in a forestry career. Suggestthat they present their findings inposters that include information suchas the geographic locations whereforestry professionals work, specificcourses that are necessary, areas ofresearch, and issues in the industry.

Resources Society of AmericanForesters; International Union ofForestry Research Organizations; U.S.Department of Agriculture ForestService

Careers in Biology

You can have students write amore extensive job description aswell as list the educational require-ments for a career in this field.

Answers to . . . The first species to popu-

late an area at the beginning of theprocess of primary succession

Figure 4–7 Stage 2: insects and spi-ders are carried in by the wind; stage3: rodents that feed on these arthro-pods and new grasses; stage 4: largermammals and birds that feed onrodents

Figure 4–8 Answers may vary. Moststudents will suggest that succession willhave proceeded in specific and pre-dictable stages and the community in20 years might be mature and stable.

96 Chapter 4

Use VisualsFigure 4–9 After students have stud-ied the figure and read the caption,ask: How is the situation shown inthis illustration an example of eco-logical succession? (Ecologicalsuccession is the series of predictablechanges that occurs in a communityover time. In this situation, the pre-dictable changes that occur are thedifferent stages in the consumption ofthe dead whale.) What is the causeof succession in this situation? (Thedeath and sinking of the whale causesthe succession.) Is the succession in amarine ecosystem more like pri-mary or secondary succession onland? (Students may compare it favor-ably to either kind of succession onland. Like primary succession, succes-sion in a marine ecosystem begins withan event, a cause. It’s also like second-ary succession in that certain oceanorganisms are adapted to the “distur-bance” of a sinking dead whale, just asland organisms are adapted to the dis-turbance of fire.)

Build Science SkillsInterpreting Graphics Collect, orask students to find, several sets ofphotographs that show areas soonafter a disturbance and at intervals assuccession occurs. Good subjects forsuch photos include areas affected bya volcanic eruption or forest fire, suchas the areas mentioned in the stu-dent text. Photos of succession afterthe eruption of Mount St. Helens arealso widely available. Display each setof photos in random order, and havestudents identify the correct order.For each set, also ask: How were youable to determine the correctorder? (Sample answer: by the typesand sizes of the plants growing in thearea)

Succession in a Marine Ecosystem Succession canoccur in any ecosystem—even in the permanently dark, deepocean. In 1987, scientists found an unusual community oforganisms living on the remains of a dead whale in the deepwaters off the coast of southern California. At first, ecologistsdid not know what to make of this extraordinary community.After several experiments and hours of observation, theecologists found that the community represented a stage insuccession amid an otherwise stable and well-documenteddeep-sea ecosystem. Since that discovery, several more whalecarcasses have been found in other ocean basins with similarorganisms surrounding them. Figure 4–9 illustrates threestages in the succession of a whale-fall community.

The disturbance that causes this kind of succession beginswhen a large whale, such as a blue or fin whale, dies and sinksto the normally barren ocean floor. The whale carcass attracts ahost of scavengers and decomposers, including amphipods(inset), hagfishes, and sharks, that feast on the decaying meat.

Within a year, most of the whale’s tissues have been eaten.The carcass then supports only a much smaller number of fishes,crabs, marine snails (inset), and other marine animals. Thedecomposition of the whale’s body, however, enriches the sur-rounding sediments with nutrients, forming an oasis of sedimentdwellers, including many different species of marine worms.

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Figure 4–9 Ecosystems areconstantly changing in responseto disturbances. In natural environments, succession occurs in stages. A dead whale that falls to the ocean floor is soon coveredwith scavengers. After a time, onlybare bones are left. The bonescontain oil that supports severaltypes of deep-sea bacteria. In thenext stage of succession, thebacteria provide energy andnutrients for a different communityof organisms that live on the bonesand in the surrounding sediments.

1

4–2 (continued)

3 ASSESSEvaluate UnderstandingHave each student select an exampleof succession—either one describedin the student text or one of his orher own choice—and write a briefdescription of the sequence ofchanges that the ecosystem couldundergo. As an alternative, studentscould draw sketches to show thechanges.

ReteachUsing photographs of ecosystemsthat you have selected from otherchapters in this textbook or fromother sources, have students list thebiotic and abiotic factors in eachecosystem.

Ecosystems and Communities 97

When only the whale’s skeleton remains, a third communitymoves in. Heterotrophic bacteria begin to decompose oils insidethe whale bones. In doing so, they release chemical compoundsthat serve as energy sources for other bacteria that arechemosynthetic autotrophs. The chemosynthetic bacteria, inturn, support a diverse community of mussels, limpets, snails,worms, crabs, clams, and other organisms that live on the bonesand within the nearby sediments.

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1. Key Concept What is thedifference between a biotic factorand an abiotic factor?

2. Key Concept Name threetypes of community interactionsthat can affect an ecosystem.

3. Key Concept What is thedifference between primary suc-cession and secondary succession?

4. How is an organism’s nichedetermined?

5. Critical Thinking Comparingand Contrasting How are thethree types of symbiotic relation-ships different? Similar?

6. Critical Thinking ApplyingConcepts Summarize the roleof organisms, including micro-organisms, in maintaining theequilibrium of a marine ecosys-tem while a dead whale decayson the ocean floor.

Creative WritingUse the information from thissection to write a short storyabout an ecosystem that isdisturbed and undergoessuccession. Hint: Include aflowchart with your story toshow the main stages ofchange.

4–2 Section Assessment

If your class subscribes to theiText, use it to review the KeyConcepts in Section 4–2.

4–2 Section Assessment1. A biotic factor is a living organism. An abiotic

factor is nonliving.2. Competition, predation, and symbiosis3. Primary succession occurs on surfaces where

no soil exists. Secondary succession occurswhen a disturbance of some kind changes anexisting community without removing the soil.

4. An organism’s niche is determined by thephysical and biological conditions in its envi-ronment and how it uses those conditions.

5. In mutualism, both species benefit. In com-mensalism, only one species benefits; the otheris neither helped nor harmed. In parasitism,one species benefits; the other is harmed. Inall three, two species live closely together.

6. Students should describe how scavengers anddecomposers eat the decaying meat, how thedecomposition of the whale’s body forms anoasis for sediment dwellers, and how bacteriadecompose the oils inside the whale’s bones.

Let students use any ecosystemand any kind of disturbance oftheir choice. In general, students’stories should include informationabout a change in the biotic orabiotic factors in a stable ecosys-tem, resulting in succession.Students should chronicle thegradual changes that return theecosystem to a climax community.If students have a hard time get-ting started, suggest that theybegin by making a flowchart ofsteps in succession for a particularecosystem and then use the flow-chart as an outline for the story.

98 Chapter 4

1 FOCUSObjectives4.3.1 Explain what microclimates

are.4.3.2 Identify the characteristics of

major land biomes.

Vocabulary PreviewHave students recall the definition ofclimate they learned earlier. Writemicroclimate on the board, and drawa box around the prefix micro-. Ask avolunteer to find the meaning of theprefix in a dictionary. Micro- means“small”; thus the term microclimateliterally means “small climate”—a climate that exists over a small area.

Reading StrategyEncourage students to create a tablefor recording the characteristics ofeach biome. Suggest that theyinclude the following columns: Nameof Biome, Temperature, Precipitation,Soil Type, Dominant Plants, DominantAnimals, and a final column labeledOther Characteristics in which torecord any information that does notfit in the previous columns.

2 INSTRUCT

Biomes and Climate Use Community ResourcesTake students on a tour of the schoolgrounds or immediate neighborhoodto look for microclimates. Examplesmight include a south-facingembankment along a roadway; thesunny south side and shaded northside of a building; and the shaded,damp environment beneath a groupof trees. Encourage students to checkeach microclimate periodically andnote any changes—for example,spring flowers blooming along abuilding’s south side.

Ecologists group Earth’s diverse environments into biomes.A is a complex of terrestrial communities that covers

a large area and is characterized by certain soil and climateconditions and particular assemblages of plants and animals.

Can all kinds of organisms live in every biome? No. Speciesvary in their adaptations to different conditions. An adaptationis an inherited characteristic that increases an organism’sability to survive and reproduce.

The leaves of the saguaro cactus, for example, are reduced tospines to minimize water loss, and its stems store water duringdry spells. Its shallow, wide-spreading roots absorb waterrapidly. Desert rodents, such as kangaroo rats, have adaptationsin their kidneys that help conserve water, and they extractwater from food. Many rain forest plants, such as certainanthuriums, have long, thin leaves whose pointed tips help shedexcess water. Some rain forest animals, such as certain treefrogs, spend their life in trees—their tadpoles grow in waterpockets in leaf bases of plants such as bromeliads.

These sorts of variations in plants and animals help differentspecies survive under different conditions in different biomes.Plants and animals also exhibit variations in orability to survive and reproduce under conditions that differfrom their optimal conditions. Plants and animals of the Arizonadesert, for example, can tolerate temperatures that range fromblisteringly hot to below freezing. Some rain forest plants andanimals, by comparison, die quickly if the temperature dropsbelow freezing or rises above 34°C for long. Either too much ortoo little of any environmental factor can make it difficult for anorganism to survive. A saguaro would rot and die in a rain forest

as surely as an anthurium or rain forest tree frogwould shrivel and die in the desert!

Biomes and ClimateBecause each species is adapted to certain conditions,the climate of a region is an important factor in deter-mining which organisms can survive there. Evenwithin a biome, precise conditions of temperatureand precipitation can vary over small distances. Theclimate in a small area that differs from the climatearound it is called a For example,certain streets in San Francisco are often blanketedin fog while the sun shines brightly just a few blocksaway. Two main components of climate—temperatureand precipitation—can be summarized in a graphcalled a climate diagram, as shown in Figure 4–10.

microclimate.

tolerance,

biome

4–3 Biomes

Key Concept• What are the unique

characteristics of the world’smajor biomes?

Vocabularybiome • tolerancemicroclimate • canopyunderstory • deciduousconiferous • humustaiga • permafrost

Reading Strategy: Using Visuals Before youread, preview Figure 4–11.Write down the names of thedifferent biomes. As you read,examine the photographs andlist the main characteristics ofeach biome.

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New Orleans, Louisiana

� Figure 4–10 Climate diagramsshow the average temperature andprecipitation at a given locationduring each month of the year. Inthis graph, and the others to follow,temperature is plotted as a red line.Precipitation is shown as verticalpurple bars. InterpretingGraphics What is the approximateaverage temperature and precipita-tion in New Orleans during the monthof July?

SECTION RESOURCES

Print:

• Teaching Resources, Section Review 4–3• Reading and Study Workbook A,

Section 4–3• Adapted Reading and Study Workbook B,

Section 4–3• Issues and Decision Making,

Issues and Decisions 46• Investigations in Forensics, Investigation 2• Lesson Plans, Section 4–3

Technology:

• iText, Section 4–3• Transparencies Plus, Section 4–3

Tim

eSaver

Section 4–3

Build Science SkillsInterpreting Tables and GraphsTo ensure that students understandthe format of a climate diagram, askquestions about Figure 4–10, such asthe following: In which month doesNew Orleans have the least precipi-tation? (October) The mostprecipitation? (July) What generaltrend do you see in the averagemonthly temperatures throughoutthe year? (Temperatures are lowest inwinter, rise through the spring, arehighest in summer, and declinethrough the fall and early winter.)

The Major BiomesUse VisualsFigure 4–11 Direct students’ atten-tion to the map and ask: Whichbiomes are found in the UnitedStates, not including Alaska andHawaii? (Temperate grassland, desert,temperate woodland and shrubland,northwestern coniferous forest andtemperate forest) Which biomes arefound in Alaska? (Temperate forest,boreal forest, and tundra)

Build Science SkillsInferring Direct students to lookback at Figure 4–2 on page 88 andcompare it with Figure 4–11 on thispage. Ask: Why do you think scien-tists classify land biomes into 10categories when there are onlythree major climate zones onEarth? (Conditions vary somewhatwithin each climate zone, so severalbiomes may occur in some climatezones.)

Ecosystems and Communities 99

The Major BiomesEcologists recognize at least ten different biomes. Theworld’s major biomes include tropical rain forest, tropi-cal dry forest, tropical savanna, desert, temperate grass-land, temperate woodland and shrubland, temperateforest, northwestern coniferous forest, boreal forest, andtundra. Each of these biomes is defined by a unique set ofabiotic factors—particularly climate—and a characteris-tic assemblage of plants and animals. The distribution ofmajor biomes is shown in Figure 4–11, and some of their mostimportant characteristics are summarized over the next fivepages.

There is often ecological variation within a biome.Sometimes, this variation is due to changes in microclimatecaused by differences in exposure or elevation above sea level.Other times, variation may be related to local soil conditions orthe presence of rock outcroppings. Note also that althoughboundaries between biomes on this map appear to be sharp,there are often transitional areas in which one biome’s plantsand animals become less common, whereas organisms of theadjacent biome become more common. These variations indistribution often can be related to the ranges of tolerances ofplants and animals for different environmental factors. As youlook at Figure 4–11 and the following pages, see if you can relatethe characteristics and locations of biomes to the patterns ofglobal winds and ocean currents in Figure 4–3.

� Figure 4–11 This map showsthe locations of the world’s majorbiomes. Other parts of Earth’ssurface are classified as mountains or ice caps. Each biome has acharacteristic climate and com-munity of organisms. Thesecharacteristics are shown on thepages that follow.

30° N

60° N

30° S

60° S

0° Equator

0 3000 Kilometers

0 3000 Miles

1500

1500

Tropical rain forest

Tropical dry forest

Tropical savanna

Temperate grassland

Desert

Temperate woodlandand shrubland

Temperate forest

Northwesternconiferous forestBoreal forest(Taiga)

Tundra

Mountains andice caps

For: Earth’s Biomes activityVisit: PHSchool.comWeb Code: cbp-2043

Answer to . . . Figure 4–10 During the month ofJuly in New Orleans, the average tem-perature is 25°C and the averageprecipitation is 200 mm.

Comprehension: Prior KnowledgeBeginning Have the students locate theirnative country on the biome map in Figure4–11. Ask the students to use the key to identi-fy the biome of their native country and thebiome of their current home in the UnitedStates. Point out the names of the biomes inthe figure’s key, and read the names out loudto model correct pronunciation.

Intermediate Pair ESL students with Englishproficient students to prepare two lists. One listshould contain words or phrases that describethe biome, climate, and common organisms oftheir native country. The other list should con-tain words or phrases that describe the biome,climate, and common organisms of their cur-rent home in the United States. Have thestudents add examples to their list by usingpictures from newspapers and magazines.

SUPPORT FOR ENGLISH LANGUAGE LEARNERS

For: Earth’s Biomes activityVisit: PHSchool.comWeb Code: cbe-2043Students compare and contrastthe temperatures and rainfalllevels of the different biomes.

100 Chapter 4

Build Science SkillsComparing and ContrastingGuide students through the wealthof information on pages 100–104 byhaving them focus on a single factorat a time across all the biomes. Forexample, first have students comparethe biomes’ temperature ranges andsequence them from lowest to high-est. (Tundra, boreal forest, temperateforest, northwestern coniferous forest,temperate grassland, temperate wood-land and shrubland, desert, tropicalsavanna, tropical rain forest, tropicaldry forest) Then, have students com-pare the biomes’ precipitation andsequence those amounts from lowestto highest. (Desert and tundra, borealforest, temperate woodland and shrub-land, temperate grassland, temperateforest, tropical savanna, tropical dryforest, northwestern coniferous forest,tropical rain forest) Next, have stu-dents compare the types of plantsthat are dominant in each biomeand, finally, the dominant animals.Discuss any biome features or organ-isms that are unfamiliar to students.Encourage students to share any per-sonal experiences they have had withdifferent land biomes.

Address MisconceptionsSome students may have the miscon-ception that all areas in tropicalregions receive a great amount ofrainfall all the time. Explain that it istrue that many areas have abundantrainfall because of frequent thunder-storms caused by local heating of theair. Currents in the atmosphere, how-ever, are extremely complex, and insome regions wind patterns result inmuch less precipitation than is foundin regions with tropical rain forests.The result is that the tropics containdry forests, savannas, and evendeserts.

Golden LionTamarin

Toucan

Tropical Rain ForestTropical rain forests are home to morespecies than all other biomes combined.The leafy tops of tall trees—extendingfrom 50 to 80 meters above the forestfloor—form a dense covering called a

In the shade below the canopy,a second layer of shorter trees and vinesforms an Organic matter thatfalls to the forest floor quickly decomposes,and the nutrients are recycled.

� Abiotic factors: hot and wetyear-round; thin, nutrient-poor soils

� Dominant plants: broad-leavedevergreen trees; ferns; large woodyvines and climbing plants; orchids andbromeliads

� Dominant wildlife: herbivoressuch as sloths, tapirs, and capybaras;predators such as jaguars; anteaters;monkeys; birds such as toucans,parrots, and parakeets; insects such asbutterflies, ants, and beetles; piranhasand other freshwater fishes; reptilessuch as caymans, boa constrictors, andanacondas

� Geographic distribution: partsof South and Central America, South-east Asia, parts of Africa, southernIndia, and northeastern Australia

understory.

canopy.

Tropical dry forests grow in places whererainfall is highly seasonal rather than year-round. During the dry season, nearly all thetrees drop their leaves to conserve water. Atree that sheds its leaves during a particularseason each year is called

� Abiotic factors: generally warmyear-round; alternating wet and dryseasons; rich soils subject to erosion

� Dominant plants: tall, deciduoustrees that form a dense canopy duringthe wet season; drought-tolerantorchids and bromeliads; aloes andother succulents

� Dominant wildlife: tigers;monkeys; herbivores such as elephants,Indian rhinoceroses, hog deer; birdssuch as great pied hornbills, piedharriers, and spot-billed pelicans;insects such as termites; reptiles suchas snakes and monitor lizards

� Geographic distribution: partsof Africa, South and CentralAmerica, Mexico, India, Australia,and tropical islands

deciduous.

Tropical Dry Forest

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What’s soil got to do with it?Soil is a mixture of rock, mineral ions, and organicmatter. Each land biome tends to have a charac-teristic soil type. The top layer of soil in tropicalrain forest biomes is acidic, with light-coloredhumus. The subsoil consists of iron and aluminum

compounds mixed with clay. The soil in desertbiomes is dry, brown to reddish brown with vari-able accumulations of clay, calcium carbonate,and soluble salts. A humus-mineral mixture existsin a thin layer of topsoil.

BACKGROUND

4–3 (continued)

Build Science SkillsCommunicating Divide the classinto 10 groups, and assign a differentbiome to each group. Tell studentsthat each group is to serve as the“class experts” on its assigned biome.Let each group’s members divideresponsibilities among themselveshowever they wish. For example, onestudent could handle abiotic factors,another student the dominant plants,and a third student the dominantanimals. Encourage groups to doresearch to gain additional informa-tion about the biomes. Provide anopportunity for each group to pres-ent its biome to the class, shareadditional information they havegathered, and answer other students’questions.

Address MisconceptionsMost students—in fact, most peoplein general—think that all deserts arehot as well as dry. Emphasize that it isthe amount of precipitation, not thetemperature range, that distinguishesthe desert from other biomes.Encourage students to find out aboutcold deserts, including the high-altitude deserts of Mongolia andChina and the Great Basin in thewestern United States.

Ecosystems and Communities 101

Receiving more seasonal rainfall thandeserts but less than tropical dry forests,tropical savannas, or grasslands, arecharacterized by a cover of grasses.Savannas are spotted with isolated treesand small groves of trees and shrubs.Compact soils, fairly frequent fires, andthe action of large animals such asrhinoceroses prevent some savanna areasfrom turning into dry forest.

� Abiotic factors: warm tempera-tures; seasonal rainfall; compact soil;frequent fires set by lightning

� Dominant plants: tall, perennialgrasses; sometimes drought-tolerantand fire-resistant trees or shrubs

� Dominant wildlife: predatorssuch as lions, leopards, cheetahs,hyenas, and jackals; aardvarks;herbivores such as elephants, giraffes,antelopes, and zebras; baboons; birdssuch as eagles, ostriches, weaverbirds, and storks; insects such astermites

� Geographic distribution: largeparts of eastern Africa, southern Brazil,and northern Australia

All deserts are dry—in fact, a desert biomeis defined as having annual precipitationof less than 25 centimeters. Beyond that,deserts vary greatly, depending onelevation and latitude. Many undergoextreme temperature changes during thecourse of a day, alternating between hotand cold. The organisms in this biomecan tolerate the extreme conditions.

� Abiotic factors: low precipitation;variable temperatures; soils rich inminerals but poor in organic material

� Dominant plants: cacti and othersucculents; creosote bush and otherplants with short growth cycles

� Dominant wildlife: predators suchas mountain lions, gray foxes, andbobcats; herbivores such as mule deer,pronghorn antelopes, desert bighornsheep, and kangaroo rats; bats; birdssuch as owls, hawks, and roadrunners;insects such as ants, beetles, butterflies,flies, and wasps; reptiles such astortoises, rattlesnakes, and lizards

� Geographic distribution: Africa,Asia, the Middle East, United States,Mexico, South America, and Australia

Desert

Tropical Savanna

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NubianVulture

WhiteRhinoceros

GoldenEagle

Desert HairyScorpion

Convergent evolutionPlants and animals that appear to be quite similaroften are found in similar environments but inwidely separated parts of the world. For example,a member of the cactus family that grows indeserts of the southwestern United States is simi-lar in appearance to a member of the spurge

family that grows in the deserts of southwesternAfrica. It would seem that these plants haveevolved from a common ancestor, but this is notthe case. The two species evolved from plantsthat are not related. This phenomenon of similaryet unrelated species occurring in different partsof the world is known as convergent evolution.

FACTS AND FIGURES

102 Chapter 4

Build Science SkillsComparing and ContrastingHave students refer back to thebiome map in Figure 4–11 on page99. Ask: Which biome makes up thelargest portion of the continentalUnited States? (Temperate grassland)Then, direct students to review theclimate diagrams and text descrip-tions of the temperate grasslandbiome on this page and the tropicalsavanna biome on page 101. Ask:What is the major similaritybetween these two biomes? (Thedominant plants are grasses.) Whatare the major differences in thetwo biomes’ climate? (The savannagets more rainfall and has a greaterrange between the highest and lowestamounts. Savanna temperatures arehigher but less variable than temperategrassland temperatures.)

Make ConnectionsEarth Science Ask students: What isthe difference in the soils of tem-perate grassland and temperatewoodland and shrubland?(Temperate grassland has fertile soils,whereas temperate woodland andshrubland has nutrient-poor soils.)Have students compare the climatediagrams for the two biomes. Explainthat soil is a combination of mineraland organic matter, and climate isperhaps the most influential factor insoil formation. Temperature and pre-cipitation determine the kind ofweathering, which determines thecharacteristics of the minerals thatmake up the soil. In addition, climatealso is the main factor in the growthof vegetation and the abundance ofmicroorganisms in the soil, both ofwhich affect the soil’s characteristics.Point out that just as the soils helpdetermine the kind of vegetationfound in a biome, the vegetation inturn contributes to how rich the soilsare, since it’s primarily the vegetationof an area that contributes the organ-ic material in a rich soil.

Temperate Grassland

Temperate Woodlandand Shrubland

Characterized by a rich mix of grasses andunderlaid by some of the world’s mostfertile soils, temperate grasslands—such asplains and prairies—once covered vastareas of the midwestern and central UnitedStates. Since the development of the steelplow, however, most have been convertedto agricultural fields. Periodic fires andheavy grazing by large herbivores maintainthe characteristic plant community.

� Abiotic factors: warm to hot sum-mers; cold winters; moderate, seasonalprecipitation; fertile soils; occasional fires

� Dominant plants: lush, perennialgrasses and herbs; most are resistantto drought, fire, and cold

� Dominant wildlife: predators suchas coyotes and badgers—historicallyincluded wolves and grizzly bears;herbivores such as mule deer, pronghornantelopes, rabbits, prairie dogs, andintroduced cattle—historically includedbison; birds such as hawks, owls,bobwhites, prairie chickens, mountainplovers; reptiles such as snakes; insectssuch as ants and grasshoppers

� Geographic distribution:central Asia, North America, Australia,central Europe, and upland plateaus ofSouth America

This biome is characterized by a semiaridclimate and a mix of shrub communitiesand open woodlands. In the open wood-lands, large areas of grasses and wildflowerssuch as poppies are interspersed with oaktrees. Communities that are dominated byshrubs are also known as chaparral. Thegrowth of dense, low plants that containflammable oils makes fires a constant threat.

� Abiotic factors: hot, dry sum-mers; cool, moist winters; thin,nutrient-poor soils; periodic fires

� Dominant plants: woodyevergreen shrubs with small, leatheryleaves; fragrant, oily herbs that growduring winter and die in summer

� Dominant wildlife: predatorssuch as coyotes, foxes, bobcats, andmountain lions; herbivores such asblacktailed deer, rabbits, and squirrels;birds such as hawks, California quails,warblers and other songbirds; reptilessuch as lizards and snakes; butterflies

� Geographic distribution:western coasts of North and SouthAmerica, areas around the Mediter-ranean Sea, South Africa, and Australia

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PrairieChicken

Black-TailedPrairie Dog

Coyote

CaliforniaSlender Salamander

More on soilThe topsoil of temperate grassland biomes tendsto be dark, alkaline, and rich in humus. This top-soil layer extends downward for more than ameter. Because topsoil formed on grasslands is

often very fertile, most of the world’s crops aregrown on grassland soils. The subsoil consists ofclay and calcium compounds. Soil in the borealforest biomes is often quite acidic.

BACKGROUND

4–3 (continued)

Build Science SkillsApplying Concepts Point out thatthe temperate forest biome in north-eastern regions of North America andAsia is noted for its striking colored fallfoliage. If students do not live in anarea that experiences this seasonalchange, urge them to collect photo-graphs of fall foliage. Also suggest thatthey obtain booklets and other touristguides that describe the best timesand locations for foliage viewing atdifferent latitudes within the biome.

Build Science SkillsClassifying Collect photographs ofvarious types of animals that arecharacteristic of each major landbiome. Number the photographs,and display them in random order.Working individually or in pairs, stu-dents should try to determine thebiome(s) in which each animal mightlive. In a follow-up class discussion,let students compare their choicesand explain their reasoning.

Ecosystems and Communities 103

Temperate forests contain a mixture ofdeciduous and coniferous (koh-NIF-ur-us)trees. trees, or conifers,produce seed-bearing cones and mosthave leaves shaped like needles. Theseforests have cold winters that halt plantgrowth for several months. In autumn, the deciduous trees shed their leaves. Inthe spring, small plants burst out of theground and flower. Soils of temperateforests are often rich in (HYOO-mus), a material formed from decayingleaves and other organic matter thatmakes soil fertile.

� Abiotic factors: cold to moderatewinters; warm summers; year-roundprecipitation; fertile soils

� Dominant plants: broadleafdeciduous trees; some conifers;flowering shrubs; herbs; a ground layer of mosses and ferns

� Dominant wildlife: Deer; blackbears; bobcats; nut and acorn feederssuch as squirrels; omnivores such asraccoons and skunks; numeroussongbirds; turkeys

� Geographic distribution: easternUnited States; southeastern Canada;most of Europe; and parts of Japan,China, and Australia

humus

Coniferous

Mild, moist air from the Pacific Oceanprovides abundant rainfall to this biome.The forest is made up of a variety ofconifers, ranging from giant redwoodsalong the coast of northern California tospruce, fir, and hemlock farther north.Moss often covers tree trunks and theforest floor. Flowering trees and shrubssuch as dogwood and rhododendron arealso abundant. Because of its lush vegeta-tion, the northwestern coniferous forest issometimes called a “temperate rain forest.”

� Abiotic factors: mild tempera-tures; abundant precipitation duringfall, winter, and spring; relatively cool,dry summer; rocky, acidic soils

� Dominant plants: Douglas fir, Sitkaspruce, western hemlock, redwood

� Dominant wildlife: bears; largeherbivores such as elk and deer;beavers; predators such as owls, bob-cats, and members of the weasel family

� Geographic distribution:Pacific coast of northwestern UnitedStates and Canada, from northernCalifornia to Alaska

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NorthwesternConiferous Forest

Temperate Forest

TigerBeetle

WhitetailDeer

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Layers of plant growthIn a temperate forest, there may be up to fivelayers of plant growth. The tallest trees make upthe canopy layer; often this layer consists of onlyone or two dominant species. Under the canopyis a layer of shorter trees called the understory.

Below the understory is a shrub layer made up ofshort, branching, woody plants. An herb layerconsisting of grasses, ferns, and annual wildflow-ers grows close to the ground. Finally, there is theground layer, which consists of mosses, fungi,and leaf litter.

FACTS AND FIGURES

104 Chapter 4

Build Science SkillsDrawing Conclusions Focus stu-dents’ attention on the climatediagram for the tundra biome. Ask:In terms of precipitation through-out the year, which other biomedoes the tundra most resemble?(The desert biome) Have students lookback at the biome map on page 99.Ask: Why does the tundra biomehave the lowest temperatures of allthe biomes? (The tundra is the far-thest north of all biomes, so it receivesthe sun’s rays at the lowest angles andfor the shortest periods of time.)

Other Land AreasMake ConnectionsEarth Science Display a large worldmap that shows Earth’s major moun-tain ranges. Have students locate thecolor-coded mountain areas on thebiome map in Figure 4–11, page 99,and then find those areas on thelarge map and list the names of themountain ranges. Separate groupscould investigate each range’s char-acteristics—the heights of its tallestpeaks, the temperature ranges anddominant organisms at various eleva-tions, and other data. Encouragestudents to also search out interest-ing facts about the ranges, such asthe 1998 discovery of mummifiedchildren on high Andean peaks ortales of the elusive Yeti (“abominablesnowman”) high in the Himalayas.Let groups share their findings in oralreports, illustrated displays, or three-dimensional models.

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Tundra

The tundra is characterized by a layer of permanently frozen subsoil.During the short, cool summer, the groundthaws to a depth of a few centimeters andbecomes soggy and wet. In winter, thetopsoil freezes again. This cycle of thawingand freezing, which rips and crushes plantroots, is one reason that tundra plants aresmall and stunted. Cold temperatures,high winds, the short growing season, andhumus-poor soils also limit plant height.

� Abiotic factors: strong winds; lowprecipitation; short and soggysummers; long, cold, and dark winters;poorly developed soils; permafrost

� Dominant plants: ground-huggingplants such as mosses, lichens, sedges,and short grasses

� Dominant wildlife: a few residentbirds and mammals that can with-stand the harsh conditions; migratorywaterfowl, shore birds, musk ox, Arcticfoxes, and caribou; lemmings andother small rodents

� Geographic distribution:northern North America, Asia, andEurope

permafrost,

SnowyOwl

Caribou

Lynx

Moose

Boreal Forest

Along the northern edge of the temperatezone are dense evergreen forests ofconiferous trees. These biomes are calledboreal forests, or (TY-guh). Wintersare bitterly cold, but summers are mildand long enough to allow the ground tothaw. The word boreal comes from theGreek word for “north,” reflecting thefact that boreal forests occur mostly in theNorthern Hemisphere.

� Abiotic factors: long, coldwinters; short, mild summers; moder-ate precipitation; high humidity;acidic, nutrient-poor soils

� Dominant plants: needleleafconiferous trees such as spruce and fir;some broadleaf deciduous trees; small,berry-bearing shrubs

� Dominant wildlife: predatorssuch as lynxes and timber wolves andmembers of the weasel family; smallherbivorous mammals; moose andother large herbivores; beavers;songbirds and migratory birds

� Geographic distribution: NorthAmerica, Asia, and northern Europe

taiga

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Oases in the tundraAs an example of the tundra’s extreme dryness: Inthe Arctic regions north of mainland Canada, lessthan 15 cm of precipitation falls annually—aboutthe same amount as falls in the desert regions ofArizona. Such dryness, coupled with intense cold,makes the tundra a barren place. Yet, like the

oases in deserts, there are areas where livingthings can survive and even thrive. Some of theseareas are sheltered valleys that are protected frombitterly cold winds. Other areas are meadowswith an abundant water supply that can supportlarge numbers of animals.

FACTS AND FIGURES

4–3 (continued)

3 ASSESSEvaluate UnderstandingBriefly describe characteristics of vari-ous biomes, and call on students atrandom to identify each one. Forexample, if you say, “High tempera-tures that do not vary muchthroughout the year,” studentsshould identify the biome as a tropi-cal rain forest or a tropical savanna.Base your descriptions on the infor-mation presented on pages 100–104of the student text.

ReteachMake overhead transparencies of theclimate diagrams for each of the landbiomes. Project the diagrams in anyorder. For each diagram, call on onestudent to summarize the diagram’sinformation about temperature andprecipitation (for example, “High tem-peratures and heavy rainfallyear-round”), and call on a secondstudent to identify the biome.

Ecosystems and Communities 105

Other Land Areas Some areas of land on Earth do not fall neatlyinto the major biome categories described on theprevious pages. These areas include mountainranges and polar ice caps.

Mountain Ranges Mountain ranges can befound on all continents. On mountains like theone in Figure 4–12, the abiotic and biotic condi-tions vary with elevation. As you move up frombase to summit, temperatures become colder andprecipitation increases. Therefore, the types ofplants and animals also change. If you were toclimb the Rocky Mountains in Colorado, forexample, you would begin in a grassland. Then,you would pass through an open woodland ofpines. Next, you would hike through a forest ofspruce and other conifers. Near the summit, youwould reach open areas of wildflowers andstunted vegetation resembling tundra. In theCanadian Rockies, ice fields occur at the peaks of some ranges.

Polar Ice Caps The icy polar regions thatborder the tundra are cold year-round. Outside ofthe ice and snow, plants and algae are few but doinclude mosses and lichens. In the north polarregion, the Arctic Ocean is covered with sea ice,and a thick ice cap covers most of Greenland.Polar bears, seals, insects, and mites are thedominant animals. In the south polar region, thecontinent of Antarctica is covered by a layer of icethat is nearly 5 kilometers thick in some places.There, the dominant wildlife includes penguinsand marine mammals.

� Figure 4–12 Washington’s Mount Rainier towersabove the tree line. Applying Concepts Based onwhat you have seen in the previous pages, which biomelies at the base of this mountain?

NSTA

For: Links on biomesVisit: www.SciLinks.orgWeb Code: cbn-2043

1. Key Concept List themajor biomes, and give onecharacteristic feature of each.

2. How are biomes classified?3. What are the two types of tropical

forest? How do they differ? 4. How might a mountain range

affect the types of plants andanimals found in an area?

5. Critical Thinking InferringWhat characteristics would youexpect tundra animals to have?

6. Critical Thinking Comparingand Contrasting Choose twovery different biomes. From eachbiome, select a plant and ananimal that are dominant.Compare how these plants’adaptations are suited to theirbiomes. Compare how theseanimals’ adaptations are suited totheir biomes.

4–3 Section AssessmentCreating ArtworkChoose one of the biomesdiscussed in this section.Then, depict the biome in apiece of artwork. Include thebiome’s characteristic plantand animal life in your art.Add labels to identify theorganisms, and write acaption describing thecontent of the artwork.

Answer to . . .

Figure 4–12 Boreal forest

This activity can be completedindividually or in small groups.Provide students with a variety ofmaterials to choose from, includ-ing basic art supplies, modelingclay, pasta shapes, pipe cleaners,fabric, and construction paper.You might also encourage stu-dents to bring materials fromhome, or you might coordinatethis activity with an art class atyour school. Encourage studentsto be creative but accurate indepicting the biomes.

NSTA

Download a worksheet on biomes for students to com-plete, and find additional teachersupport from NSTA SciLinks.

If your class subscribes to theiText, use it to review the KeyConcepts in Section 4–3.

4–3 Section Assessment1. Students should list the major biomes along

with one characteristic of each.2. By their climate, which is determined by

precipitation and temperature, and by thecommunity of organisms that live there

3. Tropical rain forests have higher tempera-tures and more rainfall annually than dotropical dry forests.

4. Animals and plants found in mountainranges must be adapted to the generally

cooler, wetter conditions that are foundthere.

5. Sample answer: Tundra animals need to bewell insulated with thick coats of fur/hair orlayers of feathers.

6. Answers may vary. Students might select anyplants and animals mentioned in the profilesof the 10 biomes. In their comparisons, theyshould discuss specific adaptations of theorganisms.

106 Chapter 4

1 FOCUSObjectives4.4.1 Identify the factors that gov-

ern aquatic ecosystems.4.4.2 Identify the two types of

freshwater ecosystems.4.4.3 Describe the characteristics of

the marine zones.

Vocabulary PreviewPoint out the words photic andaphotic in the Vocabulary list on thispage. Explain that phot- in thesewords means the same thing as theprefix photo- in words such as photo-graph. Ask: What does the prefixphoto- mean? (“Light”) What doesthe prefix a- in the word aphoticmean? (“Not” or “without”) What doyou think the terms photic andaphotic mean? (“With light” and“without light”) Tell students to checktheir predictions when theyencounter these words in the text.

Reading StrategyAs with the biomes in Section 4–3,have students set up a table forrecording the similarities and differ-ences they find as they read aboutaquatic ecosystems. Suggest thatthey divide the “Marine Ecosystems”section of the table into two subsec-tions so they can keep separate noteson the photic and aphotic zones.

2 INSTRUCT

FreshwaterEcosystemsUse Community SourcesHave students consult road maps tofind the locations and names of anyfreshwater ecosystems—lakes, ponds,rivers, or streams—in their area. Ifpossible, arrange a trip to one ofthese locations so students canobserve its characteristics and thetypes of organisms living there.

Nearly three fourths of Earth’s surface is covered with water,so it is not surprising that many organisms make their

homes in aquatic habitats. Oceans, streams, lakes, andmarshes—indeed, nearly any body of water—contain a widevariety of communities. These aquatic communities are gov-erned by biotic and abiotic factors, including light, nutrientavailability, and oxygen.

Aquatic ecosystems are determined primarily bythe depth, flow, temperature, and chemistry of the over-lying water. In contrast to land biomes, which are groupedgeographically, aquatic ecosystems are often grouped accordingto the abiotic factors that affect them. One such factor is thedepth of water, or distance from shore. The depth of water, inturn, determines the amount of light that organisms receive.Water chemistry refers primarily to the amount of dissolvedchemicals—especially salts, nutrients, and oxygen—on whichlife depends. For example, communities of organisms found inshallow water close to shore can be very different from the commu-nities that occur away from shore in deep water. One abiotic factorthat is important both to biomes and aquatic ecosystems is lati-tude. Aquatic ecosystems in polar, temperate, and tropical oceansall have distinctive characteristics.

Freshwater EcosystemsIt may surprise you to know that only 3 percent of the surfacewater on Earth is fresh water. Freshwater ecosystemscan be divided into two main types: flowing-waterecosystems and standing-water ecosystems.

Flowing-Water Ecosystems Rivers, streams, creeks, andbrooks are all freshwater ecosystems that flow over the land.Organisms that live there are well adapted to the rate of flow.Some insect larvae have hooks that allow them to take hold of

aquatic plants. Certain catfish have suckers that anchor them torocks. Trout and many other fishes have streamlined bodies

that help them move with or against the current.Flowing-water ecosystems like the river in Figure 4–13

originate in mountains or hills, often springing from anunderground water source. Near the source, the

turbulent water has plenty of dissolved oxygenbut little plant life. As the water flows downhill,

sediments build up and enable plants toestablish themselves. Farther down-

stream, the water may meander moreslowly through flat areas, where

turtles, beavers, or river ottersmake their homes.

4–4 Aquatic Ecosystems

Key Concepts• What are the main factors that

govern aquatic ecosystems?• What are the two types of

freshwater ecosystems?• What are the characteristics of

the different marine zones?

Vocabularyplankton • phytoplanktonzooplankton • wetlandestuary • detritus • salt marshmangrove swampphotic zone • aphotic zonezonation • coastal oceankelp forest • coral reefbenthos

Reading Strategy: Making Comparisons Asyou read, write down state-ments about similarities anddifferences among the differenttypes of aquatic ecosystems.

� Figure 4–13 The MenomineeRiver in Michigan is a flowing-waterecosystem. Like all aquaticecosystems, this river’s communi-ties are determined by the depth,flow, and chemistry of the water.

SECTION RESOURCES

Print:

• Teaching Resources, Section Review 4–4• Reading and Study Workbook A, Section 4–4• Adapted Reading and Study Workbook B,

Section 4–4• Lesson Plans, Section 4–4

Technology:

• iText, Section 4–4• Transparencies Plus, Section 4–4

Tim

eSaver

Section 4–4

Build Science SkillsComparing and ContrastingAs suggested for biomes, guide stu-dents through the information in thissection by having them focus on onefactor at a time—temperature range,light, oxygen and nutrient availabili-ty, and characteristic organisms—across all the aquatic ecosystems.Discuss any unfamiliar organisms,and provide field guides so studentscan do further research. Also, encour-age students to share any personalexperiences they have had with dif-ferent aquatic biomes.

DemonstrationCollect several different types offreshwater plants and animals to setup a classroom aquarium. Also collectsome abiotic elements—water, rocks,mud, sand, and the like—so theorganisms will have as natural anenvironment as possible. Make sureyou or students return all organismsto their original location at the end ofthis unit.

Use Community ResourcesEmphasize that a particular area ofland is classified as a wetland not bywhether it has water on it at any par-ticular time of the year but by its soiltype and the plants found there. Infact, many freshwater wetlands aredry for a good part of the year, sopeople may not even recognize themas wetlands. If a wetland exists nearthe school, take the class to observeit. Caution students to be very carefulwalking in the area, as many wetlandplants are fragile and the soil, ifdamp, can be easily compacted. Donot allow students to collect anyplants, animals, or abiotic materials.

Ecosystems and Communities 107

Standing-Water Ecosystems Lakes and ponds are themost common standing-water ecosystems. In addition to the netflow of water in and out of these systems, there is usually watercirculating within them. This circulation helps to distributeheat, oxygen, and nutrients throughout the ecosystem.

The relatively still waters of lakes and ponds provide habitatsfor many organisms, such as plankton, that would be quicklywashed away in flowing water. is a general term for thetiny, free-floating organisms that live in both freshwater andsaltwater environments. See Figure 4–14 for examples. Unicellularalgae, or (fyt-oh-PLANK-tun), are supportedby nutrients in the water and form the base of many aquatic foodwebs. Planktonic animals, or (zoh-oh-PLANK-tun),feed on the phytoplankton.

What are phytoplankton?

Freshwater Wetlands A is an ecosystem in whichwater either covers the soil or is present at or near the surface ofthe soil for at least part of the year. The water in wetlands maybe flowing or standing and fresh, salty, or brackish, which is amixture of fresh and salt water. Many wetlands are very produc-tive ecosystems that serve as breeding grounds for insects, fishesand other aquatic animals, amphibians, and migratory birds.

The three main types of freshwater wetlands are bogs,marshes, and swamps. Bogs, which are wetlands that are oftendominated by sphagnum moss, typically form in depressions wherewater collects. The water in sphagnum bogs is often very acidic.Marshes are shallow wetlands along rivers. They may be under-water for all or part of the year. Marshes often contain cattails,rushes, and other tall, grasslike plants. Water flows slowly throughswamps, which often look like flooded forests. The presence of treesand shrubs is what distinguishes a swamp from a marsh.

Some wetlands, such as the swamp shown in Figure 4–15,are wet year-round. Other kinds of wetlands, however, may notalways be covered in standing water. Such areas may be classi-fied as wetlands because they have certain kinds of soils and arewet enough to support a specific community of water-lovingplants and animals.

wetland

zooplankton

phytoplankton

Plankton

� Figure 4–14 Both freshwaterand saltwater ecosystems ofteninclude plankton. This photographshows phytoplankton, zooplankton,and larger animals called water fleas.Predicting What might happen toan aquatic food web if phytoplanktonwere removed from the ecosystem?

� Figure 4–15 Freshwaterecosystems can be divided intotwo main types: flowing-waterecosystems and standing-waterecosystems. Although this swampalong the Loxahatchee River inFlorida appears stagnant, wateractually flows through it slowly. Theswamp is home to turtles, otters,alligators, and herons that liveamong the baldcypress trees.

Answers to . . . Single-celled algae

Figure 4–14 The consumers woulddie off because there would be no moreproducers to sustain them.

Less Proficient ReadersFew students will have observed any marineecosystems beyond the intertidal zone. To helpstudents comprehend the text description ofmarine zones, provide a wide variety of visualresources—photographic books, nature maga-zines, videotapes, and CD-ROMs—so studentscan see what the different zones and theirorganisms look like.

Advanced LearnersStudents who need an additional challengemight enjoy researching and reading aboutSylvia Earle, a marine biologist who earnedinternational recognition for her pioneeringstudies of hydrothermal vents and the uniqueorganisms found there. Encourage students toshare their findings in posters, oral reports,mock radio shows, or skits.

108 Chapter 4

Estuaries

A detritivore is an organism that eatsdetritus.

Build Science SkillsComparing and ContrastingHave students describe similaritiesand differences between the types oforganisms found in freshwaterecosystems and those found in estu-aries. Then, ask: Do the samespecies of aquatic organisms live inboth ecosystems? (No) Why not?(Estuaries are saltwater ecosystems.Species usually are adapted to live ineither a saltwater environment or afreshwater environment, not both.)

Marine EcosystemsBuild Science SkillsPredicting Draw a horizontal lineon the chalkboard to represent thesurface of the ocean. Then, draw adiagonal line slanting downward,and mark it to indicate ocean depthsof 50 meters, 100 meters, 200meters, 1000 meters, 2000 meters,and 10,000 meters. Invite students torelate what they already know aboutmarine organisms. Then, ask: Whatfactors do you think determine thetypes of organisms that live at dif-ferent depths in the ocean? (Moststudents will realize that available lightis a major factor. Accept all responseswithout comment at this time.)

Detritus is a Latin wordmeaning “worn away.” Inecology, detritus refers toparticles that have worn awayfrom decaying organic mate-rial. If the Latin word voraremeans “to devour,” what is adetritivore?

Estuaries(ES-tyoo-ehr-eez) are wetlands formed where rivers

meet the sea. Estuaries thus contain a mixture of fresh waterand salt water, and are affected by the rise and fall of oceantides. Many are shallow, so sufficient sunlight reaches thebottom to power photosynthesis. Primary producers includeplants, algae, and both photosynthetic and chemosyntheticbacteria. Estuary food webs differ from those of more familiarecosystems because most primary production is not consumedby herbivores. Instead, much of that organic material enters thefood web as detritus. is made up of tiny pieces oforganic material that provide food for organisms at the base ofthe estuary’s food web. Organisms that feed on detritus includeclams, worms, and sponges.

Estuaries support an astonishing amount of biomass,although they usually contain fewer species than freshwater ormarine ecosystems. Estuaries serve as spawning and nurserygrounds for commercially important fishes and for shellfish suchas shrimps and crabs. Many young animals feed and grow inestuaries, then head out to sea to mature, and return to repro-duce. Many waterfowl use estuaries for nesting, feeding, andresting during migrations.

are temperate-zone estuaries dominated bysalt-tolerant grasses above the low-tide line, and by seagrassesunder water. Salt marshes like the one shown in Figure 4–16(left) are (or were once) found along great stretches of easternNorth America from southern Maine to Georgia. One of thelargest systems of connected salt marshes in America surroundsthe Chesapeake Bay estuary in Maryland.

shown in Figure 4–16 (right), arecoastal wetlands that are widespread across tropical regions,including southern Florida and Hawaii. Here, the dominant plantsare several species of salt-tolerant trees, collectively called man-groves. Seagrasses are also common below the low-tide line. Likesalt marshes, mangrove swamps are valuable nurseries for fishand shellfish. The largest mangrove area in the continental UnitedStates is within Florida’s Everglades National Park.

Mangrove swamps,

Salt marshes

Detritus

Estuaries

Figure 4–16 Salt marshes occur inestuaries along seacoasts in thetemperate zone. Salt-tolerant grassesare the dominant plants in this saltmarsh (left) along the coast of MountDesert Island in Maine. Mangroveswamps (right) occur in bays andestuaries along tropical coasts. Thestiltlike roots of mangrove trees trapsediment that accumulates as mudbehind the trees. This allows otherplants to take root and helps to buildthe mangrove forest out from theshoreline. Predicting Would youexpect to find mangrove swamps orsalt marshes on a coast exposed tolarge ocean waves? Explain.

Bottoms up!A problem that occurs in aquatic ecosystems isthat nutrients tend to sink below the photiczone so organisms cannot use them. In lakes,strong winds usually mix the water. In oceans,deep nutrient-rich water rises to the photic zonein a process called upwelling. In upwelling,winds carry surface water away from land.

Bottom water with valuable nutrients is pulledup into the photic zone to replace the surfacewater that has been moved out to sea. Thesenutrients support vigorous and rapid growth ofphytoplankton, which provide the basis formarine food webs. Upwelling is common alongthe coastal margins of continents, where windscarry surface currents toward the open ocean.

FACTS AND FIGURES

4–4 (continued)

Build Science SkillsProblem Solving Explain that threemain factors determine the types ofmarine organisms that live at differ-ent depths: available sunlight, watertemperature, and water pressure.Ask: At what depth do you thinksunlight is most abundant? (Nearthe surface) How does this factoraffect where organisms live?(Organisms that conduct photosynthe-sis live near the surface, as do manyanimals that depend on those organ-isms for food.) At what depth wouldyou expect water temperatures tobe the warmest? Why? (Near thesurface, because sunlight warms thewater there) How do you thinkwater pressure changes with oceandepth? (Pressure increases as depthincreases.) How would this factoraffect where organisms live? (Mostorganisms cannot withstand greatpressure on their bodies, so they mustlive near the surface.)

Use VisualsFigure 4–17 Have students locatethe intertidal zone, coastal ocean,open ocean, and benthic zone on thefigure and identify the characteristicorganisms pictured for each of thefour zones. Ask: What are the abiot-ic characteristics of each zone?(Intertidal zone: extreme changes inconditions from being submerged insea water to being exposed to air, sun-light, and heat; subject to waves andcurrents. Coastal ocean: receives sun-light. Open ocean: surface receivessunlight; deep ocean has high pressure,frigid temperatures, and total darkness.Benthic zone: includes ocean floor, vari-ous ocean depths, and deep-sea vents.)

Ecosystems and Communities 109

Land

Coastalocean

OpenoceanBenthic zone

Continentalshelf

Photic zone

Aphotic zone

200 m

Continental slope andcontinental rise

Abyssalplain

Oceantrench

Intertidal z

one

1,000 m

4,000 m

6,000 m

10,000 m

Marine EcosystemsUnless you are an avid diver or snorkeler, it takes some imagi-nation to picture what life is like in the vast, three-dimensionalocean. Sunlight penetrates only a relatively short distancethrough the surface of the water. Photosynthesis is limited tothis well-lit upper layer known as the (FOH-tik) Only in this relatively thin surface layer—typically down to adepth of about 200 meters—can algae and other producers grow.Below the photic zone is the (ay-FOH-tik) whichis permanently dark. Chemosynthetic autotrophs are the onlyproducers that can survive in the aphotic zone.

There are several different classification systems that scien-tists use to describe marine ecosystems. In addition to thedivision between the photic and aphotic zones, marinebiologists divide the ocean into zones based on the depthand distance from shore: the intertidal zone, the coastalocean, and the open ocean. Each of these zones supportsdistinct ecological communities. The benthic zone covers theocean floor and is, therefore, not exclusive to any of the othermarine zones. Figure 4–17 shows a generalized diagram of themarine zones.

What factor is absent in the aphotic zone?

zone,aphotic

zone.photic

� Figure 4–17 The ocean canbe divided into zones based on lightpenetration and into zones basedon depth and the distance fromshore. Each zone contains a character-istic assemblage of organisms.

For: Links on aquatic ecosystems

Visit: www.SciLinks.orgWeb Code: cbn-2044

NSTA

Answers to . . . Sunlight

Figure 4–16 No, because largeocean waves would make it impossiblefor the roots of salt marsh grasses ormangrove trees to remain anchored.

NSTA

Download a worksheeton aquatic ecosystems for studentsto complete, and find additionalteacher support from NSTASciLinks.

110 Chapter 4

Build Science SkillsClassifying To reinforce students’understanding of which organismslive in which zone, provide a varietyof once-living ocean organisms forstudents to examine. Possibilitiesinclude dried sea stars and seaurchins, seashells, crab and lobstershells, dried kelp and other seaweed,pieces of coral, and dried, pickled, orfresh squid or octopus. Challengestudents to sort the objects intogroups based on the zones in whichthe living organisms are found.

Intertidal Zone Organisms that live in the inter-tidal zone are exposed to regular and extreme changes

in their surroundings. Once or twice a day, they aresubmerged in sea water. The remainder of the time,they are exposed to air, sunlight, and temperaturechanges. Often, organisms in this zone are batteredby waves and sometimes by strong currents.

There are many different types of intertidalcommunities. One of the most interesting is the rocky

intertidal, shown in Figure 4–18, which exists in tem-perate regions where exposed rocks line the shore. There,

barnacles and seaweed permanently attach themselves tothe rocks. Other organisms, such as snails, sea urchins, and seastars, cling to the rocks by their feet or suckers.

Competition among organisms in the rocky intertidal zoneoften leads to zonation (zoh-NAY-shun). is the promi-nent horizontal banding of organisms that live in a particularhabitat. In the rocky intertidal zone, each band can be distin-guished by differences in color or shape of the major organisms.For example, a band of black algae might grow at the highest high-tide line, followed by encrusting barnacles. Lower down, clusters ofblue mussels might stick out amid clumps of green algae. Thiszonation is similar to the pattern that you might observe as youclimb up a mountain. In the intertidal zone, however, zonationexists on a smaller vertical scale—just a few meters compared tothe kilometers you would ascend on a mountain.

Coastal Ocean The extends from thelow-tide mark to the outer edge of the continental shelf, therelatively shallow border that surrounds the continents.The continental shelf is often shallow enough to fall mostlyor entirely within the photic zone, so photosynthesis canusually occur throughout its depth. As a result, the coastalocean is often rich in plankton and many other organisms.

One of the most productive coastal ocean communi-ties is the kelp forest. are named for theirdominant organism: a giant brown alga that can grow atextraordinary rates—as much as 50 centimeters a day.Huge forests of this seaweed are found in cold-temperateseas around the world, including those along the coastsof California and the Pacific Northwest. Kelp forests, likethe one shown in Figure 4–19, support a complex foodweb that includes snails, sea urchins, sea otters, a varietyof fishes, seals, and whales.

What is the coastal ocean?

Kelp forests

coastal ocean

Zonation

� Figure 4–19 Kelp forests are ecosystems that occur in coastaloceans. The long strands of kelp create a habitat that shelters avariety of organisms. This kelp forest off the coast of California ispart of a larger zone of kelp forests found along the western coastof North America from Alaska to Mexico. Comparing andContrasting How is a kelp forest like a forest on land?

� Figure 4–18 The maindivisions in the ocean based ondepth and distance from shore arethe intertidal zone, the coastalocean, and the open ocean. Alongthe coast of Vancouver Island inCanada, low tide reveals sea stars,seaweed, and other organismsadapted to life in the intertidal zone.

The ocean floorThe benthic zone, or ocean floor, extends fromthe high-tide mark to the deepest part of theocean. Life in this zone consists of sessile andmotile organisms. These organisms are distributedfrom near the shore to the depths of the oceanand they play an important role in the ocean’sfood chain. Plants found in the benthic zone canlive only in the photic zone, or area where sun-light can penetrate (30 to 200 meters below theocean’s surface). The portion of the benthic zone

that is between 2000 meters and 6000 metersdeep is known as the abyssal zone. The floor ofthe abyssal zone is covered with mud and organicdebris. For the most part, food is in short supply.However, there are fishes (rattails), echinoderms,mollusks, and burrowing worms. In areas aroundhydrothermal vents (volcanic hot springs), clumpsof bacteria growing on rocks use the hydrogensulfide as an energy source. Living on these bacte-ria are filter-feeding animals such as giant clamsand giant tube worms (up to 3.7 meters long).

BACKGROUND

4–4 (continued)

Ecosystems and Communities 111

Ecosystem ProductivityThe data table on the right compares the primaryproductivity of some of the world’s ecosystems. Usethe data table to answer the following questions:

1. Using Tables and Graphs Construct a bar graphto display the data. Use different colors to distin-guish aquatic and land ecosystems.

2. Using Tables and Graphs According to yourgraph, which ecosystem is most productive? Usewhat you know to explain that fact.

3. Inferring Although the open ocean is among theleast productive ecosystems, it contributes greatlyto the overall productivity of the biosphere. Howcan this situation be explained?

4. Applying Concepts What are two abiotic factorsthat might account for the differences in productiv-ity among the land ecosystems in the table? (Hint:Review the relevant biomes on pages 100–104.)

Productivity of Aquaticand Land Ecosystems

Ecosystem

Average PrimaryProductivity (gramsof organic matterproduced per squaremeter per year)

Aquatic Ecosystems:

Coral reef

Estuary

Lake

Open ocean

Land Ecosystems:

Tropical rain forest

Temperate forest

Tropical savanna

Tundra

2500

1800

500

125

2200

1250

900

90

Coral Reefs In the warm, shallow water of tropical coastaloceans are coral reefs, among the most diverse and productiveenvironments on Earth. are named for the coralanimals whose hard, calcium carbonate skeletons make up theirprimary structure. As you can see in Figure 4–20, an extraordinarydiversity of organisms flourishes in these spectacular habitats.

Coral animals are tiny relatives of jellyfish that live togetherin vast numbers. Most coral animals are the size of your finger-nail, or even smaller. Each one looks like a small sack with amouth surrounded by tentacles. These animals use their tenta-cles to capture and eat microscopic creatures that float by. Coralanimals cannot grow in cold water or water that is low in salt.

The types of corals that build reefs grow with the help of algaethat live symbiotically within their tissues. These algae carry outphotosynthesis using the coral animals’ wastes as nutrients. In turn,the algae provide their coral hosts with certain essential carboncompounds. Because their algae require strong sunlight, most reef-building corals thrive only in brightly lit areas within 40 meters ofthe surface.

Coral reefs

� Figure 4–20 This coral reef off the island of New Britain in the PacificOcean supports a dazzling variety of corals and fishes. Reefs are mostabundant around islands and along the eastern coasts of continents. In theUnited States, only the coasts of southern Florida and Hawaii have coralreefs. Applying Concepts In what types of community interactions arecoral animals involved?

Answers to . . . The part of the ocean

that extends from the low-tide mark tothe outer edge of the continental shelf

Figure 4–19 Students’ comparisonsshould include the idea that the pro-ducers in a kelp forest ecosystem—giant kelp—have a function similar tothe producers in a forest on land.

Figure 4–20 Coral animals areinvolved in predation both as predatorsand as prey. They are also involved in amutualistic symbiotic relationship withalgae. Students might also infer thatcorals are involved in competition andare affected by parasitism and disease.

Build Science SkillsUsing Analogies Direct students toconsider what they learned aboutmountains when they studied biomesin the previous section. Then, ask:How is the benthic zone like anupside-down mountain? (Sampleanswer: As you go up a mountain,temperatures become colder and pre-cipitation increases, producing differentconditions at different elevations.Similarly, as you go farther down in theocean and the water depth increases,pressure also increases, available sun-light decreases, and temperaturesbecome colder, producing differentzones along the ocean floor.)

Before students graph the data, havethem review the characteristics of thelisted types of ecosystems.1. Students should choose a scale forthe axis of the graph representingaverage primary productivity that islarge enough to enable them tograph the data accurately.2. Coral reef ecosystems are the mostproductive. Students may infer thatreefs are so productive because theyare near the top of the photic zone.3. The area of the open ocean farexceeds the area occupied by all theother ecosystems put together.4. Latitude and precipitation are bothfactors that affect the productivity ofthe land ecosystems in the table.Ecosystems that are drier (tropicalsavanna) or closer to the polarzones (tundra) are less productive.

112 Chapter 4

Use VisualsFigure 4–21 Focus students’ atten-tion on the photo of the octopus,and ask: Since this animal livesmainly on the ocean floor, can it beclassified as a benthos organism?(Yes, but not exclusively so. Someoctopi live in the depths of oceans, butothers live in shallow coastal waters.)Point out that marine animals canadapt to different environments, justas land animals can.

3 ASSESSEvaluate UnderstandingAs you did with biomes in the previ-ous section, describe various aquaticecosystems and ocean zones, and callon students at random to identifyeach one. Limit your descriptions tothe information contained in this section.

ReteachHave students work cooperatively toconstruct a bulletin board displayshowing the different kinds of aquat-ic ecosystems and ocean zonesdiscussed in this section, using pic-tures they have drawn themselves orphotocopied. Have students label thenames of the aquatic ecosystems andocean zones, their major characteris-tics, and the types of organismsfound in each.

Open Ocean The open ocean, often referred to as theoceanic zone, begins at the edge of the continental shelf and

extends outward. It is the largest marine zone, coveringmore than 90 percent of the surface area of the world’s

oceans. The open ocean ranges from about 500 meters deepalong continental slopes to more than 11,000 meters at the

deepest ocean trench. Organisms in the deep ocean are exposedto high pressure, frigid temperatures, and total darkness.

Typically, the open ocean has very low levels of nutrients andsupports only the smallest producers. Productivity is generallylow. Still, because of the enormous area, most of the photosyntheticactivity on Earth occurs in the part of the open ocean within thephotic zone. Fishes of all shapes and sizes dominate the openocean. The swordfish and the octopus in Figure 4–21 are just twoexamples of the organisms found in this zone. Marine mammalssuch as dolphins and whales also live there but must stay close tothe surface to breathe.

Benthic Zone The ocean floor contains organisms that liveattached to or near the bottom, such as sea stars, anemones,and marine worms. Scientists refer to these organisms as the

That is why the ocean floor is called the benthic zone.This zone extends horizontally along the ocean floor from thecoastal ocean through the open ocean.

Benthic ecosystems often depend on food from organismsthat grow in the photic zone, particularly the producers. Animalsthat are attached to the bottom or do not move around much,such as clams and sea cucumbers, feed on pieces of dead organicmaterial, or detritus, that drift down from the surface waters.Near deep-sea vents, where superheated water boils out ofcracks on the ocean floor, dwell chemosynthetic primary pro-ducers that support life without light and photosynthesis.

benthos.� Figure 4–21 In the openocean, the swordfish (top) cansometimes be seen swimming nearthe surface, yet these fish can alsodive to more than 600 meters toprey on fishes of the deep ocean.Some types of octopus (bottom) livein the depths of the open ocean,although other types live in shallowcoastal waters.

1. Key Concept List threecharacteristics that determine thestructure of aquatic ecosystems.

2. Key Concept Comparestanding-water ecosystems toflowing-water ecosystems. Howare they alike? How are theydifferent?

3. Key Concept List sixdistinct ecological zones that canbe found in the ocean. Give twoabiotic factors for each zone.

4. Define the terms wetland andestuary. Give at least one exampleof a freshwater wetland and of anestuary.

5. Critical Thinking PredictingHow might the damming of ariver affect an estuary at theriver’s mouth?

Comparing andContrastingChoose three different aquaticecosystems. From each of theseecosystems, select a plant andan animal and describe howthe organisms are adapted totheir environments. Showcomparisons. Hint: Create atable to organize your ideas.

4–4 Section Assessment

4–4 (continued)

If your class subscribes to theiText, use it to review the KeyConcepts in Section 4–4.

Answers may vary. Students mightselect any plants and animals fromthree of the aquatic ecosystemsdiscussed in this section. In theircomparisons, they should describehow specific adaptations of theorganisms help them live in theirenvironments

4–4 Section Assessment1. Any three of these four: depth, flow, temper-

ature, and chemistry of overlying water2. Alike: freshwater ecosystems; water contains

oxygen and nutrients. Different: Water in aflowing-water ecosystem moves rapidly nearthe source and slows near the mouth. Waterin a standing-water ecosystem has little netflow but circulates within the system.

3. Photic zone, aphotic zone, intertidal zone,coastal ocean, open ocean, benthic zone;

and the abiotic factors for each.4. A wetland is an ecosystem in which water

either covers the soil or is present at or nearthe surface of the soil for some of the year.An estuary is a wetland where a river meetsthe sea. Check students’ examples.

5. Without fresh water from the river, thebrackish estuary water would become saltier,changing the kinds of organisms that couldsurvive in that ecosystem.