5 unit ecology · each of the variety of organisms on earth depends in some way on other living and...

Coral reef communities are second only to rain forests in diversity.

18 Introductionto Ecology

19 Populations

20 Community Ecology

21 Ecosystems

22 Humans and theEnvironment

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CHAPTERSCHAPTERS

ECOLOGY“We and our fellow vertebrates are largely along for

the ride on this planet. If we want to perpetuate the

dream that we are in charge of our destiny and that

of our planet, it can only be by maintaining biological

diversity—not by destroying it. In the end, we impoverish

ourselves if we impoverish the biota.”From “Diverse Considerations,” by Thomas E. Lovejoy from Biodiversity,edited by E. O. Wilson. Copyright © 1988 by the National Academy of Sciences.Reproduced by permission of National Academy Press.

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Tropical rain forests are richer in speciesthan other areas of Earth are.

The biosphere

Mimicry helps this mantid hide from both predators and potential prey.

Bears are among the largest terrestrial predators.

357

357

CHAPTER

18 INTRODUCTION TO ECOLOGYPlanning Guide

Compression GuideTo shorten instructionbecause of time limitations,omit Section 1.

Chapter Opener

Section 1 Introduction to Ecology• Identify a key theme in ecology.• Describe an example showing the effects of inter-

dependence upon organisms in their environment.• Identify the importance of models to ecology.• State the five different levels of organization at which

ecology can be studied.

Section 2 Ecology of Organisms• Compare abiotic factors with biotic factors, and list

two examples of each.• Describe two mechanisms that allow organisms to

survive in a changing environment.• Explain the concept of the niche.

TE Activity Abiotic and Biotic Factors, p. 363 ◆bTE Activity Tolerance, p. 364 gTE Internet Activity Niche/Habitats, p. 365SE Exploration Lab Observing Habitat Selection,

pp. 378–379 ◆gHBS Skills Practice Labs Assessing Abiotic Factors in

the Environment* ◆a

TE Activity Freshwater Producers, p. 367 ◆gTE Activity Observing Plant Detritivores,

p. 368 ◆gHBS Biotechnology Labs Oil-Degrading

Microbes* ◆a

OSP Parent LetterCD Student Edition on CD-ROMCD Guided Reading Audio CD

TR E1 Making an Ecosystem Model*TR E2 Levels of Organization*CD Visual Concepts CD-ROM

TR E3 Earthworm Niche*CD Visual Concepts CD-ROMVID Biology Lab Video Observing How

Brine Shrimp Select a Habitat

TR E4 Trophic Levels*TR E5 Food Chain in an Antarctic

Ecosystem*TR E6 Food Web in an Antarctic

Ecosystem*TR E7 Grassland Food Web* TR E8 Energy Transfer Through

Trophic Levels*TR E9 Four Trophic Levels in an Aquatic

Ecosytem*TR E10 Amount of Energy at Four

Trophic Levels*TR E11 Energy Efficiency in Food

Consumption*CD Visual Concepts CD-ROM

pp. 358–362

358A C H A P T E R 1 8 I n t r o d u c t i o n t o E c o l o g y

OBJECTIVES LABS, DEMONSTRATIONS, AND ACTIVITIES TECHNOLOGY RESOURCESPACING • 45 min

pp. 363–365PACING • 90 min



Section 3 Energy Transfer• Summarize the role of producers in an ecosystem.• Identify several kinds of consumers in an ecosystem.• Explain the important role of decomposers in

an ecosystem.• Compare the concept of a food chain with that

of a food web. • Explain why ecosystems usually contain only a few

trophic levels.

TE Group Activity Interconnected Organisms, p. 360 b

TE Internet Activity Ecosystems, p. 360HBS Quick, Data, and Math Labs Evaluating

Biodiversity*g

SE Chapter Highlights, p. 375SE Chapter Review, p. 376TR Graphic Organizer*gTR Concept Mapping*g

ANC Vocabulary Review*gANC Quizzes*gANC Chapter Test*gANC Chapter Test*a

SE Standardized Test Prep, p. 377OSP Test GeneratorOSP Test Item Listing

CHAPTER REVIEW, ASSESSMENT, ANDSTANDARDIZED TEST PREPARATION

PACING • 90 min

TR E12 Water Cycle*TR E13 Carbon Cycle*TR E14 Nitrogen Cycle*CD Visual Concepts CD-ROM

SE Quick Lab Modeling Groundwater, p. 372 ◆gANC Datasheets for In-Text Labs Modeling

Groundwater*gTE Internet Activity Cycles of Mater, p. 373

ANC Forensics Labs Solubility and Chemical Fertilizers(CBL™)* ◆g

Section 4 Ecosystem Recycling• List four major biogeochemical cycles.• Summarize three important processes in the water cycle.• Outline the major steps in the carbon cycle.• Describe the role of decomposers in the nitrogen cycle. • Summarize the major steps of the phosphorus cycle.

Visit go.hrw.com to find avariety of online resources.Click Holt Online Learningfor an online edition of this textbook and otherinteractive resources.

This DVD package includes: • Holt Calendar Planner• Customizable Lesson Plans• Editable Worksheets• MindPoint® Quiz Show• Holt PowerPoint® Resources

• ExamView® Version 6.0Assessment Suite

• Interactive Teacher’s Edition• Holt PuzzlePro®

Online and Technology Resources

KEY SE Student Edition OSP One-Stop Planner VID Classroom Video/DVDTE Teacher Edition TR Transparencies and * Also on One-Stop Planner

ANC Ancillary Workbook Transparency Worksheets ◆ Requires advance prepHBS Holt BioSources Lab Program CD CD or CD-ROM

TE Using the Figure Global Biosphere, p. 358ANC Science Skills Worksheet*gANC Critical Thinking Worksheet*a

TE Reading Skill Builder Interactive Reading, p. 359 bTE Using the Figure Lyme Disease, p. 360 gTE Skill Builder Science Literacy, p. 361 gTE Reading Skill Builder Exploring Primary Sources, p. 361 a

ANC Active Reading Guide*

TE Skill Builder Interpreting Graphics, p. 364 bTE Reading Skill Builder Vocabulary, p. 364 b


TE Reading Skill Builder Active Reading, p. 366 gTE Using the Figure Primary Productivity, p. 367 gTE Skill Builder Writing Skills, p. 367 bTE Inclusion Strategies, p. 367TE Using the Figure Food Webs, p. 368 g


TE Reading Skill Builder Word Origins, p. 371 bTE Using the Figure Nitrogen Cycle, p. 373 gTE Inclusion Strategies, p. 373


TE Assessing Prior Knowledge, p. 358ANC Study Guide*g

SE Section Review, p. 362 gTE Reteaching, p. 362 bTE Quiz, p. 362 g

SE Section Review, p. 365 gTE Reteaching, p. 365 bTE Quiz, p. 365 g

SE Section Review, p. 369 gTE Reteaching, p. 369 ◆bTE Quiz, p. 369 g

National Science EducationStandards

LSInter3, LSInter5, UCP1, UCP2,HNS2

LSInter3, LSInter4, LSInter5,LSMat2, LSMat5, HNS1, HNS2

LSInter2, LSInter3, LSInter5,LSMat2, LSMat3, UCP1, SI1, PS5,ESS1, HNS2, HNS3

LSInter1, LSInter5, LSMat1,LSMat5, ESS2, PS2, PS6, SPSP3

C H A P T E R 1 8 P l a n n i n g G u i d e 358B

SKILLS DEVELOPMENT RESOURCES REVIEW AND ASSESSMENT CORRELATIONS

SE Section Review, p. 374 gTE Reteaching, p. 374 bTE Quiz, p. 374 gTE Alternative Assessment, p. 375 gTE Study Tip, p. 375 g

Maintained by the National ScienceTeachers Association.

www.scilinks.orgClassroom CD-ROMs

• Guided Reading Audio Program• Student One Stop• Virtual Investigations• Visual Concepts• Dissection Labs

Classroom Videos

• Lab Videos demonstratethe chapter lab.

Holt Lab GeneratorCD-ROM

Search for any lab by topic, standard,difficulty level, or time. Edit any lab to fit your needs, or create your own labs.Use the Lab Materials QuickList softwareto customize your lab materials list.

358 C H A P T E R 1 8

CHAPTER 18Using the FigureGlobal Biosphere Have studentsexamine the photograph of Earthfrom space. Ask students to inferthe relationship between the planetand ecology. Tell students thatthe photograph represents thebiosphere, where all living organ-isms interact with one anotherand the physical environment.

Visual

Assessing PriorKnowledgeReview the following conceptswith students.

Evolution (Ch. 15): Ask studentshow a constantly changing envi-ronment might affect evolution.(Populations can evolve by naturalselection with respect to heritable traitsthat favor reproductive success and sur-vivorship in each particular environment.)Ask them if people have an impacton the environment.

Matter, Energy, and Organization(Ch. 2): Ask students to tracebackward the source of the foodthey had for their last meal.(Students may trace their meal to plant-eating animals or to plant materials.) Tellstudents that plants are part of thefirst trophic level of an ecosystem.Plants are producers that makeenergy-storing molecules that otherorganisms depend on.

GENERAL

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Standards Correlations

National Science Education Standards

LSInter1 The atoms and molecules on the earth cycleamong the living and nonliving components of the biosphere.

LSInter2 Energy flows through ecosystems in one direction,from photosynthetic organisms to herbivores to carnivoresand decomposers.

LSInter3 Organisms both cooperate and compete in ecosystems.

LSInter4 Living organisms have the capacity to producepopulations of infinite size, but environments and resourcesare finite.

LSInter5 Human beings live within the world’s ecosystems.

LSMat1 All matter tends toward more disorganized states.

LSMat2 The energy for life primarily derives from the sun.

LSMat3 The chemical bonds of food molecules contain energy.

LSMat5 The distribution and abundance of organisms andpopulations in ecosystems are limited by the availability of matter and energy and the ability of the ecosystems to recycle matter.

ESS1 Energy in the earth system

ESS2 Geochemical cycles

Ecology is the study of the interactionsof organisms with each other and withthe nonliving parts of Earth. This imageis a view of Earth as seen from space.

SECTION 1 Introduction to Ecology

SECTION 2 Ecology of Organisms

SECTION 3 Energy Transfer

SECTION 4 Ecosystem Recycling

18CHAPTER INTRODUCTION TO

ECOLOGYINTRODUCTION TOECOLOGY

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I N T R O D U C T I O N T O E C O L O G Y 359

OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describes a key theme in ecology, interde-pendence, and explains the levelsof organization in ecology. Thesection also covers the use ofmodels in science.

Emphasize to students that a setof crucial interactions takes placebetween living organisms and theliving and nonliving environment.Have students brainstorm exam-ples of interdependence. (Answersmay include mutualistic symbioses suchas ant-fungus interactions and living-nonliving relationships such as thedependence of plants on water or soil.)

Logical

Identifying PreconceptionsHuman Interdependence Somestudents may have the preconcep-tion that humans are not depend-ent on other organisms or theenvironment. Discuss an examplethat illustrates human dependence.Have students brainstorm otherexamples to include in the discus-sion. (Examples may include the effectsof crop failures or drought on humanpopulations. A relatively recent examplewould be the outbreak of the hantavirusinfections on the Navajo Reservation inArizona and Utah caused by an increasein the rodent population, which was triggered by abundant piñon nuts in the 1990s.) Interpersonal

Interactive Reading AssignChapter 18 of the Modern BiologyGuided Reading Audio CDProgram to help studentsachieve greater success in reading the chapter.

VerbalLS

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SECTION 1

I N T RO D U C T I O N TO

E C O L O G YEcology is the study of the interactions between organisms

and the living and nonliving components of their environment.

Each of the variety of organisms on Earth depends in some

way on other living and nonliving things in its environment.

Ecology is a broad science that involves collecting information

about organisms and their environments, observing and

measuring interactions, looking for patterns, and seeking to

explain these patterns.

INTERDEPENDENCE: A KEYTHEME IN ECOLOGY

Although the field of ecology was not named until 1866, ecologicalinformation and understanding have always been crucial tohumans. Before the development of agriculture, about10,000–12,000 years ago, our ancestors obtained all of their foodby hunting animals and gathering plants, seeds, berries, and nuts.Their survival depended on practical knowledge about the envi-ronment. Although most humans today don’t survive as hunter-gatherers, they interact with the environment and otherorganisms every day.

Organisms and Their EnvironmentsAll organisms interact with other organisms in their surroundingsand with the nonliving portion of their environment. Their survivaldepends on these interactions. Ecologists refer to this quality asinterconnectedness or interdependence.

Interdependence is a key theme found throughout ecology.For example, you could not survive without the plants and otherphotosynthetic organisms that produce oxygen. Your cells needoxygen to release the energy in food, and cells will die if deprivedof oxygen for even a few minutes. Conversely, photosyntheticorganisms depend on the release of carbon dioxide gas by thecellular respiration of other organisms, such as humans, andgeochemical processes, such as volcanic eruptions. Carbon diox-ide gas is an essential raw material for making carbohydrates byphotosynthesizers.

SECTION 1

O B J E C T I V E S

● Identify a key theme in ecology.● Describe an example showing the

effects of interdependence uponorganisms in their environment.

● Identify the importance of modelsto ecology.

● State the five different levels oforganization at which ecology canbe studied.

V O C A B U L A R Y

ecologyinterdependenceecological modelbiosphereecosystemcommunitypopulation

ecology

from the Greek oikos,meaning “house,” and

logos, meaning “study of”

Word Roots and Origins

359

STATE RESOURCES

For specific resourcesfor your state, visitgo.hrw.com and type inthe keyword HSHSTR.

TEACHER RESOURCES

Workbooks

Active Reading Guide (Section 1)

Technology

Visual Concepts CD-ROM• Levels of Ecology

Using the FigureLyme Disease Have studentsstudy Figure 18-1. Ask studentshow the abundance of acornsmight affect the incidence ofLyme disease. (During seasons whenthere is an abundance of acorns, thereare more deer and mice and, thus, moreticks. When there are fewer acorns,there are fewer deer and mice and, consequently, fewer ticks.) Visual

Group ActivityInterconnected OrganismsOrganize the students into smallgroups. Have groups brainstorma list of organisms they mightexpect to see living in their area.Take students on a walk aroundthe school grounds or in a nearbypark. Have students make a list ofall the organisms that they see.After students have made theirlists, have them discuss withintheir groups how the organismsthat they have seen are intercon-nected. After the trip, have thestudent groups make a master listof the organisms they observedand the interconnections thatthey found. Interpersonal

Ecosystems Have studentsresearch ecosystems by using theInternet Connect box on thispage. IntrapersonalLS

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360 C H A P T E R 1 8

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23

Acorns

White-tailed deer

Deermouse

Deer tick

Humans

Effects of InterdependenceA consequence of interdependence is that any change in the envi-ronment can spread through the network of interactions and affectorganisms that appear far removed from the change. One exampleis the interrelationships among species in forests in the easternUnited States. Through these relationships, as shown in Figure 18-1,acorn production is connected to the spread of Lyme disease, aninfection that can damage the human nervous system.

In most years, oak trees produce few or no acorns. Every fewyears, however, they produce a huge crop of acorns. The largenumber of acorns supports larger populations of deer and mice,which feed on acorns. Ticks feed on the blood of animals, so thetick population also increases. The increased number of ticksincreases the chance that ticks will bite any humans in the forest.The bite of the deer tick can transmit the bacterium that causesLyme disease to humans. So, in general, after a season of highacorn production, the cases of Lyme disease increase.

ECOLOGICAL MODELSEcology is extremely complex and difficult to study. One way thatecologists deal with this complexity is to use ecological models torepresent or describe the components of an ecological system. Amodel may be physical, conceptual, or mathematical. Ecologistsconstruct models to help them understand environmental interac-tions and to make predictions about possible changes. These pre-dictions can be tested by comparing them with observations fromthe natural world. Models are widely used to help plan and evalu-ate solutions to environmental problems. However, an ecologicalmodel may be limited in its application, because it cannot alwaysaccount for the influence of every variable in a real environment.

All of the different species shown areinterconnected in the forest. Anunusually plentiful crop of acorns helpssupport a large population of deer andmice. The deer and mice helpsupport a large population of ticks.

Ticks carry the bacterium that causesLyme disease. They pass on the diseaseto humans who visit the forest.

3

2

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FIGURE 18-1

www.scilinks.org

Topic: EcosystemsKeyword: HM60466

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SOCIAL STUDIESSOCIAL STUDIESCONNECTIONCONNECTION

Global Environmental ChangeEnvironmental changes have occurredthroughout the world as a result of humanimpact. Ask students to research suchchanges and show on maps of the worldwhere they have occurred. Some examplesare the gradual desertification of Africa’sSahel over the last century and the extensivedestruction of rain forests in Central orSouth America during the same period.

Teaching TipLife in the Soil Most of the life in Earth’s biosphere lives on thesurface or in the oceans. However,the soil also contains manyimportant organisms. Theseorganisms are mainly inverte-brates and microorganisms, manyof which are vital for healthyplants. Obtain a soil sample, andhave students examine the samplein a jar and under a microscope.

Visual

Science Literacy Have studentsresearch the Biosphere II Projectin Arizona. Students can then writea short research paper, composea travel brochure, or make aposter based on their research.

Verbal

Teaching TipLocal Communities Have studentsname the types of communities oforganisms that might be found inyour local area. List the differentcommunities on the board. Then,have students name all the organ-isms they can think of that belongto each community. List theorganisms on the board.

Intrapersonal

Exploring Primary SourcesAssign the Supplemental Readingworksheet titled “Silent Spring.”The worksheet can be found byvisiting go.hrw.com. Type in thekeyword HM6SRT. Verbal LS

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LEVELS OF ORGANIZATIONScientists recognize a hierarchy of different levels of organizationwithin organisms. Each organism is composed of one or moreorgans. Each organ is composed of tissues, which, in turn, are com-posed of cells, and so on. Likewise, ecologists recognize a hierar-chy of organization in the environment, as illustrated in Figure 18-2.

Each level has unique properties that result from interactionsbetween its components, so a complete study of ecology wouldlook at all levels. But for practical reasons, ecologists often focustheir research on one level of organization while recognizing thateach level is influenced by processes at other levels.

The BiosphereThe broadest, most inclusive level of organization is the biosphere(BIE-oh-SFIR), the thin volume of Earth and its atmosphere that sup-ports life. All organisms are found within the biosphere. It is about20 km (13 mi) thick and extends from about 8 to 10 km (5 to 6 mi)above the Earth’s surface to the deepest parts of the oceans. Incomparison, the Earth’s diameter is about 12,700 km (7,900 mi), ormore than 600 times the thickness of the biosphere. If Earth werethe size of an apple, the biosphere would only be as thick as theapple’s skin. Ecologists often describe the biosphere as a thin filmof life covering an otherwise lifeless planet. Living things are notdistributed evenly throughout the biosphere. Most organisms arefound within a few meters of the surface of the land or oceans.

Ecology has been organized into five levels because of the complexity of the science. This diagram is a modelillustrating the hierarchical organizationof ecology.

FIGURE 18-2

BIOSPHERE

ECOSYSTEM

COMMUNITY

POPULATION

ORGANISM

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Unusual Organisms Tell students that representative cell lines, tissue types, cell abnormalities, and diseases are kept by the American Type Culture Collection in Bethesda, Maryland. These samples help scientists to identify unusual organismsor cell types.

TEACHER RESOURCES

Workbooks

Quick, Data and Math Labs• Evaluating the Degree of

Biodiversity Around YourHome

Technology

Transparencies• E1 Making an Ecosystem Model• E2 Levels of Organization

Visual Concepts CD-ROM• Levels of Ecology

GENERAL

ReteachingComponents of the BiosphereHave students make their ownpersonal “biosphere.” Have thembegin by drawing a small circleon a sheet of paper. Ask them towrite their name inside the circlealong with the level of organizationto which they belong. (organism)Then, have them draw anothercircle outside the first one to represent a larger population,and label this circle with a popu-lation to which he or she belongs.(neighborhood, ethnic group, or religiousaffiliation) Continue this activity,using increasingly larger circles,until the entire diagram is encircledby the level of “true” biosphere.

Visual

QuizTrue or False:1.Geology is the study of the

interactions between organismsand the environment. (false,the study described is ecology)

2.The broadest level of organiza-tion in ecology is the biosphere.(true)

3.All ecological models are mathematical. (false, they can beverbal, visual, or mathematical)

GENERAL

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Answers to Section Review

1. All organisms interact with other organisms andwith their environment, so it is impossible to studyecology without investigating interdependence.

2. Sample answer: A farmer sprays insecticide on afield. The insecticide causes reduced fertility in abird species that preys on field mice. The farmer’shome becomes infested with mice.

3. Models enable scientists to simplify and betterunderstand complex processes in the environment.

4. A population contains individuals of only one species.A community contains populations of severalspecies.

5. broadest level of ecology containing all living andnonliving things

6. biosphere, ecosystem, community, population,and organism

7. If the wolf population decreased, the deer populationwould probably increase. There would be morecompetition between deer and mice for food. Thismay lead to a decrease in the mice population.

8. Sunlight is the ultimate source of energy for photo-synthetic organisms, such as plants and algae.Animals obtain their energy by consumingautotrophs or animals that eat autotrophs.

9. Yes, the biosphere includes all parts of Earth,its oceans, and atmosphere that contain life.

362 C H A P T E R 1 8

EcosystemsThe biosphere is composed of smaller units called ecosystems. Anecosystem (EK-oh-SIS-tuhm) includes all of the organisms and the non-living environment found in a particular place. Consider a pondecosystem. It contains a variety of living things, such as fish, turtles,aquatic plants, algae, insects, and bacteria. These organisms inter-act in ways that affect their survival. For instance, insects and fisheat aquatic plants, and turtles eat fish. The pond ecosystem alsoincludes all the nonliving (physical and chemical) aspects of thepond that influence its inhabitants. The chemical composition ofthe pond—its pH, its levels of dissolved oxygen and carbon dioxide,and its supply of nitrogen—helps to determine what kinds of organ-isms live in the pond and how abundant they are. A very importantphysical factor is the amount of sunlight the pond receives, becausesunlight is the ultimate source of energy for the pond’s inhabitants.

Communities, Populations, and OrganismsWhereas an ecosystem contains both living and nonliving compo-nents, a community includes only species of organisms. A communityis all the interacting organisms living in an area. For instance, all thefish, turtles, plants, algae, and bacteria in the pond described abovemake up a community. Although it is less inclusive than an ecosys-tem, a community is still very complex, and it may contain thousandsof species. Ecologists studying a community often focus on howspecies interact and how these interactions influence the nature ofthe community. Remember that the word community has a specificmeaning in biology that differs from its everyday meaning.

Below the community level of organization is the population level,where the focus is on the members of a single species. A populationincludes all the members of a species that live in one place at onetime. An example of a population of flowers is shown in Figure 18-3. The simplest level of organization in ecology is that of the organ-ism. Research at this level concentrates on the adaptations that alloworganisms to overcome the challenges of their environment.

1. Explain why interdependence is an importanttheme in ecology.

2. Describe one example of the effects of interde-pendence upon organisms in their environment.

3. Why are models used so often in the science ofecology?

4. How does a population differ from a community?

5. Define the term biosphere.

6. List the five main levels of organization inecology.

CRITICAL THINKING

7. Predicting Results Assuming wolves eat deer,how could a disease that kills a large portion ofthe wolf population affect the mice populationin an area of the eastern United States?

8. Analyzing Concepts Why is the amount of sun-light important to the animals in an ecosystem?

9. Applying Information Would bacteria thatinhabit a cave deep inside Earth be consideredpart of the biosphere? Explain.

SECTION 1 REVIEW

These flowers represent a population ofCalifornia poppies, Eschscholziacalifornica, living in California.

FIGURE 18-3

362

OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describesthat organisms continuouslyinteract with the biotic and abi-otic factors of their environmentand explains that the need tomeet biological needs underliesall interactions. This section alsodiscusses that changes are alwaysoccurring in the environment andexplains that organisms respond tochanges through adaptations thathelp provide biological stability.

Have students make a list of the ways humans have recentlychanged the environment throughpollution. (Students may list thermalpollution, by heating lakes and streams;water pollution, by disposal of detergentsand fertilizer; air pollution, as evidencedby acid rain and smog; or the ozone hole,from release of CFCs.) Ask studentsto list organisms that have beenaffected by these changes or thatpotentially could be affected.(Answers may vary.) Ask students todiscuss any changes that haveoccurred in their neighborhood,town, or county. Interpersonal

ActivityAbiotic and Biotic Factors Showstudents a picture of an aquarium.Ask students to make a list of allthe abiotic and biotic factors thataffect the survival of a fish speciesin the aquarium. (Abiotic: temperature,light, pH, and oxygen; Biotic: fish, plants,insects, other invertebrates, (algae andworms) organisms in the tank)

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E C O L O G Y O F O R G A N I S M SThe place where an organism lives is its habitat. But why

does it live there and not elsewhere? What parts of its habitat

does it use? The answers to these questions depend on an

organism’s evolutionary history, its abilities, and its needs.

ECOSYSTEM COMPONENTSEcologists separate the environmental factors that influence anorganism into two types. The living components of the environ-ment are called biotic (bie-AHT-ik) factors. Biotic factors include allof the living things that affect the organism. The nonliving factors,called abiotic (AY-bie-AHT-ik) factors, are the physical and chemicalcharacteristics of the environment.

Biotic and Abiotic FactorsAbiotic factors include temperature, humidity, pH, salinity, oxygenconcentration, amount of sunlight, availability of nitrogen, and pre-cipitation. The importance of each factor varies from environmentto environment. Abiotic and biotic factors are not independent;organisms change their environment and are influenced by thosechanges. For example, the availability of nitrogen in the soil affectshow fast plants can grow, and plants affect nitrogen availability byabsorbing nitrogen from the soil.

Abiotic factors are not constant. They vary from place to placeand over time, as shown in Figure 18-4. Consider temperature,which is a very important abiotic factor. Temperature varies fromhour to hour, from day to day, from season to season, and fromplace to place. Also important are the small differences in temper-ature within a habitat, such as the difference between an area inthe shade of a tree and an area exposed to direct sunlight.

ORGANISMS IN A CHANGINGENVIRONMENT

Each organism is able to survive within a limited range of environ-mental conditions. For example, an organism may be able to func-tion only within a specific range of temperatures. It is possible todetermine this range for an organism by measuring how efficientlyit performs at different temperatures. A graph of performance ver-sus values of an environmental variable, such as temperature, iscalled a tolerance curve.

SECTION 2

O B J E C T I V E S● Compare abiotic factors with biotic

factors, and list two examples ofeach.

● Describe two mechanisms thatallow organisms to survive in achanging environment.

● Explain the concept of the niche.

V O C A B U L A R Yhabitatbiotic factorabiotic factortolerance curveacclimationdormancymigrationniche

These pictures show the same area offorest at different times of the year. Onthe top, the forest displays springfoliage. On the bottom, the same area iscovered with snow in the winter.

FIGURE 18-4

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SECTION 2

TEACHER RESOURCES

Workbooks


Technology

Visual Concepts CD-ROM• Comparing Biotic and Abiotic Factors

ActivityTolerance Ask students to listways that people can change theirtolerance to physical factors.(Answers may include references tosome drugs: increasingly higher dosesneeded to get the same effect; tempera-tures: people living in warmer climatestolerate heat more easily than individualsliving in cold climates; and elevation:people living at higher altitudes havemore lung capacity for obtaining oxygen.)

Logical

Interpreting Graphics Have stu-dents use Figure 18-5 to answerthe following questions: Whatswimming speed do the two groupsof fish have at 20°C? (about 23cm/sfor the fish raised at 5°C and 32cm/s forthe fish raised at 25°C) At what tem-perature does the fastest swim-ming speed occur? (a speed of about40 cm/s occurs at about 29°C for fishraised at 25°C) Visual

Vocabulary An organism can beboth a conformer and a regulator.A fish may be a conformer ofenvironmental temperature but a regulator of internal salt con-centration. Verbal LS

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Trends in EcologyAcclimation Studies suggest a downside toacclimation. Results of these new studies callinto question previous laboratory findingsthat low-level metal contamination makesfish more tolerant of larger doses of metalcontamination. Scientists at the University of Colorado and the Colorado Division ofWildlife reported that brown trout were put in cages for 96 hours in an area highlypolluted by mining effluent such that no fishlived there. Fish that had previously residedin water with low-level mining effluent sur-vived only 28 hours, whereas fish fromcleaner waters survived almost 48 hours.

364 C H A P T E R 1 8

Job Description Canopy scien-tists are biologists who study the forestcanopy—the uppermost layer of trees.Today’s researchers use a variety ofequipment to reach the canopy. Canopyscientists can work in universities,botanical gardens, museums, and gov-ernment and conservation agencies.

Focus On a CanopyScientist“I’m on the edge of discovering what isnew. Plus, I get to climb trees!” NaliniNadkarni teaches at a university and con-ducts research in both tropical and tem-

perate forests. She has also invited artistsand musicians to visit the canopy. “I try tounderstand the science of the canopy, butartists and musicians help capture itsaesthetic value.” Nadkarni knows that herjob is important. The forests she studiesare important factors in world climate andare home to many unique species.

Education and Skills• High School—three years of science

courses and four years of math courses.• College—bachelor of science in biol-

ogy, including course work in botany,zoology, ecology, geography, and data

analysis; a master’s (M.S.) or doctoraldegree (Ph.D.) for research.

• Skills—self-motivation, curiosity,patience, good observation skills,research skills, computer literacy,quick thinking, and field survival skills.

Careersin BIOLOGY

Canopy Scientist

For more about careers, visitgo.hrw.com and type in thekeyword HM6 Careers.

An organism can survive and function in conditionsoutside its optimal range, but its performance is greatlyreduced. It cannot survive under conditions that fall out-side its tolerance limits. An organism’s range may bedetermined by the levels of one or more factors, such aspH, temperature, or salinity.

AcclimationSome organisms can adjust their tolerance to abiotic factorsthrough the process of acclimation (AK-luh-MAY-shuhn). Forexample, goldfish raised at different temperatures havesomewhat different tolerance curves, as shown in Figure18-5. Be sure not to confuse acclimation with adaptation.Acclimation occurs within the lifetime of an individualorganism. Adaptation is genetic change in a species or pop-ulation that occurs from generation to generation over time.

Control of Internal ConditionsEnvironments fluctuate in temperature, light, moisture, salinity, andother chemical factors. There are two ways for organisms to dealwith some of these changes in their environment. Conformers areorganisms that do not regulate their internal conditions; theychange as their external environment changes. The internal condi-tions of a conformer remain within the optimal range only as long asenvironmental conditions remain within that range. In contrast,regulators are organisms that use energy to control some of theirinternal conditions. Regulators can keep an internal condition withinthe optimal range over a wide variety of environmental conditions.

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Goldfish raised at 25°C are acclimatedto higher temperatures, so they have adifferent tolerance curve than the fishraised at 5°C do.

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MEDICINEMEDICINECONNECTIONCONNECTION

Antibiotic Resistance A serious problemin medicine today is the increasing resist-ance of disease-causing bacteria to commonantibiotics. The bacteria have genetic varia-tion that render them highly resistant tomost antibiotics. Scientists are constantlyworking to develop new types of antibiotics.However, this problem will continue to beserious, as bacteria are continually evolvingresistance to the newly developed antibiotics.

TEACHER RESOURCES

Technology

Transparencies• E3 Earthworm Niche

Visual Concepts CD-ROM• Niche, Habitat

Teaching TipMigration Ask students how theythink migration and hibernationare different solutions to the sameproblem. (Both are ways of coping withadverse conditions in the environment.)Ask students how birds benefitby laying their eggs in the spring.(The young will be mature and ready tomigrate by winter.) Logical

Niche/Habitats Have studentsresearch how niches and habitatsare interrelated by using theInternet Connect box on thispage. Intrapersonal

ReteachingSurvival Strategies Ask studentsto predict what might happen toa bird species that found itselfexposed to unusually cold tem-peratures earlier than normal.(The birds may migrate early in the seasonto a more favorable and warmer habitat.)

Logical

QuizTrue or False:1.Temperature is an example of

a biotic environmental factor.(false, it is an abiotic factor)

2.Regulators use energy to control an internal condition,such as body temperature.(true)

3.A habitat is an organism’s complete way of life. (false, this is a species’ niche)

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1. Distinguish between biotic and abiotic factors.

2. Explain how migration allows organisms to copewith a changing environment.

3. What does a tolerance curve indicate about anorganism?

4. How does an organism’s niche differ from itshabitat?

5. Give examples of a generalist and a specialistnot mentioned in the text above.

CRITICAL THINKING

6. Analyzing Concepts Why do different speciesnever occupy exactly the same niche?

7. Applying Information If some of the resourcesin a habitat are destroyed, which would be morelikely to survive, a generalist species or a spe-cialist species? Explain.

8. Drawing Conclusions A small rodent speciesand a bird species are adapted to cold tempera-tures. How might each species survive a majortemperature increase?

SECTION 2 REVIEW

Escape from Unsuitable ConditionsSome species can survive unfavorable environmental conditionsby escaping from them temporarily. For example, desert animalsusually hide underground or in the shade during the hottest partof the day. Many desert species are active at night, when temper-atures are much lower. A longer-term strategy is to enter a state ofreduced activity, called dormancy, during periods of unfavorableconditions, such as winter or drought. Another strategy is to moveto a more favorable habitat, called migration. An example ofmigration is the seasonal movements of birds, which spend springand summer in cooler climates and migrate to warmer climates inthe fall.

THE NICHESpecies do not use or occupy all parts of their habitat at once. Thespecific role, or way of life, of a species within its environment isits niche (NICH). The niche includes the range of conditions that thespecies can tolerate, the resources it uses, the methods by whichit obtains resources, the number of offspring it has, its time ofreproduction, and all other interactions with its environment.Parts of a lion’s niche are shown in Figure 18-6.Generalists are species with broad niches; they can tolerate a

range of conditions and use a variety of resources. An example of ageneralist is the Virginia opossum, found across much of the UnitedStates. The opossum feeds on almost anything, from eggs and deadanimals to fruits and plants. In contrast, species that have narrowniches are called specialists. An example is the koala of Australia,which feeds only on the leaves of a few species of eucalyptus trees.

Some species have more than one niche within a lifetime. Forexample, caterpillars eat the leaves of plants, but as adult butter-flies, they feed on nectar.

Plants and animals are able to share thesame habitats because they each havedifferent niches.

FIGURE 18-6

niche

from the Old French nichier,meaning “to nest”


www.scilinks.org

Topic: Niche/HabitatsKeyword: HM61029

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1. biotic: all living things that affect organisms; abiotic: nonliving factors, such as pH, in the environment.

2. Migration allows animals to move to a more favorable habitat.

3. A tolerance curve shows the range of conditionswithin which an organism can function.

4. Habitat is where an organism lives; niche is therole of an organism in its environment—how itobtains resources and what conditions it cantolerate.

5. Sample answer: A raccoon is a generalist becauseit uses many food resources. The larvae of a butterflyspecies may specialize on a plant species.

6. Species have unique niches. This conditionreduces competition for resources. In the sameniche, one species will outcompete the other, andeventually the other species will be eliminated.

7. A generalist species would be more likely to sur-vive, because generalists are able to use a broaderrange of resources. However, if the resource thatthe specialist uses is not affected, the survivorshipof the specialist will not be affected.

8. A rodent might be able to survive increased temperatures by becoming dormant or less activeduring the heat of the day. A bird could migrate toan area with cooler temperatures.

OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describeshow energy in an ecosystem isacquired by organisms for growthand reproduction. The sectionalso describes how energy in an ecosystem is organized intotrophic levels with correspondingproducers and consumers.

Have students think about organ-isms that are common in the localarea, and ask students to con-struct a diagram that would be atypical food chain in the area. Askstudents to try and put 6 or 7trophic levels in their food chain.(Generally, there are no more than fourtrophic levels in a food web. This is dueto the fact that a low rate of energytransfer occurs between trophic levels.)This will lead into a discussion oftrophic levels and energy. Visual

Active Reading Before studentsbegin reading the section, workwith the class to develop a list ofall the different trophic levels inan ecosystem. (producers, herbivores,small carnivores, and large carnivores)Have students read the section tosee how scientists have describedenergy flow between levels of anecosystem. VerbalLS

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366 C H A P T E R 1 8

E N E R G Y T R A N S F E RAll organisms need energy to carry out essential functions,

such as growth, movement, maintenance and repair, and

reproduction. In an ecosystem, energy flows from the sun to

autotrophs, then to organisms that eat the autotrophs, and then

to organisms that feed on other organisms. The amount of

energy an ecosystem receives and the amount that is transferred

from organism to organism affect the ecosystem’s structure.

PRODUCERSAutotrophs, which include plants and some kinds of protists andbacteria, manufacture their own food. Because autotrophs cap-ture energy and use it to make organic molecules, they are calledproducers. Recall that organic molecules are molecules that con-tain carbon.

Most producers are photosynthetic, so they use solar energy topower the production of food. However, some autotrophic bacteriado not use sunlight as an energy source. These bacteria carry outchemosynthesis (KEE-moh-SIN-thuh-sis), in which they use energystored in inorganic molecules to produce carbohydrates. In terres-trial ecosystems, plants are usually the major producers. Inaquatic ecosystems, photosynthetic protists and bacteria are usu-ally the major producers.

Measuring ProductivityGross primary productivity is the rate at which producers in anecosystem capture the energy of sunlight by producing organiccompounds. Photosynthetic producers use energy and carbondioxide to make sugar, an energy-rich organic molecule. Some ofthe sugar is used for cellular respiration, some is used for mainte-nance and repair, and some is used for making new organic mate-rial through either growth or reproduction. Ecologists refer to theorganic material that has been produced in an ecosystem asbiomass. Producers add biomass to an ecosystem by makingorganic molecules.

Only energy stored as biomass is available to other organisms inthe ecosystem. Ecologists often measure the rate at which biomassaccumulates, called the net primary productivity. Net primaryproductivity is typically expressed in units of energy per unit areaper year (kcal/m2/y) or in units of dry organic mass per unit areaper year (g/m2/y). Net primary productivity equals gross primaryproductivity minus the rate of respiration in producers.

SECTION 3

O B J E C T I V E S● Summarize the role of producers in

an ecosystem.● Identify several kinds of consumers

in an ecosystem.● Explain the important role of

decomposers in an ecosystem.● Compare the concept of a food

chain with that of a food web.● Explain why ecosystems usually

contain only a few trophic levels.

V O C A B U L A R Yproducerchemosynthesisgross primary productivitybiomassnet primary productivityconsumerherbivorecarnivoreomnivoredetritivoredecomposertrophic levelfood chainfood web

www.scilinks.org

Topic: Producers andConsumers

Keyword: HM61220

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SECTION 3

GEOLOGYGEOLOGYCONNECTIONCONNECTION

Producers as Hydrocarbon Sources Theorganic matter that forms hydrocarbons,such as oil, natural gas, and coal, comesmainly from producers. Until about 400 mil-lion years ago, the only source of organiccarbon was from producers such as algaeand photosynthetic bacteria. After theDevonian, land plants accounted for a higherpercentage of organic carbon. However, 50 to 60 percent of the world’s total organiccarbon was still produced by phytoplank-ton and bacteria in the oceans. Primaryproducers provide the energy we use in ourcars, homes, and industries today.

TEACHER RESOURCES

Workbooks


Technology

Visual Concepts CD-ROM• Comparing Consumers and Producers,

Types of Consumers, Biomass

Using the FigurePrimary Productivity Have stu-dents study Figure 18-7. Askstudents why an estuary or wet-land is more productive than afreshwater lake. (An estuary receivesnutrients drained from larger landmassesand supports marine, freshwater, andbrackish organisms.) Visual

ActivityFreshwater Producers Obtain asample of pond or stream waterthat has a heavy growth of algae.Divide the sample into Petri dishes,and provide slides, droppers, andcoverslips so that students canobserve water samples under themicroscope. Have students countthe number of green things theysee in the square of the coverslip.They should also count the num-ber of animal-like organisms (protists). Ask students whichorganism is greater in number, thealgae or the animal-like organisms,and why. Ask which species ismore numerous. (Algae are producers,and animal-like protists are consumers.It takes many producers to support eachconsumer, so producers are usuallygreater in number.) Visual

Writing Skills Have studentswrite a paragraph describing a producer, a consumer, and adetritivore that are commonlyfound in your local area. Verbal

Teaching TipProducers Most students will onlybe familiar with producers thatutilize the sun’s energy throughphotosynthesis. However, photo-synthetic organisms are not theonly producers. Chemosyntheticbacteria are also producers. Theyare important in ecosystems suchas deep-ocean hydrothermal ventcommunities. AuditoryLS

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2000As the histogram shows, the net primaryproductivity in a tropical rain forest isvery similar to the net primaryproductivity in an estuary. Temperategrasslands and freshwater lakes are alsovery similar in productivity.

FIGURE 18-7

This turkey vulture, Cathartes aura, is adetritivore that consumes dead animals.Detritivores play the important role ofcleaning up dead organisms and aidingdecomposition.

FIGURE 18-8

omnivore

from the Latin omnis,

meaning “all,” and -vore,

meaning “one who eats”


Figure 18-7 shows that net primary productivity can vary greatlybetween ecosystems. For example, the average net primary pro-ductivity in a tropical rain forest is 25 times greater than the ratein a desert of the same size. Although rain forests occupy onlyabout 5 percent of Earth’s surface, they account for almost 30 per-cent of the world’s net primary productivity. Variations in threefactors—light, temperature, and precipitation—account for mostof the variation in productivity among terrestrial ecosystems. Anincrease in any of these variables usually leads to a productivityincrease. In aquatic ecosystems, productivity is usually deter-mined by only two factors: light and the availability of nutrients.

CONSUMERSAll animals, most protists, all fungi, and many bacteria are het-erotrophs. Unlike autotrophs, heterotrophs cannot manufacturetheir own food. Instead, they get energy by eating other organismsor organic wastes. Ecologically speaking, heterotrophs areconsumers. They obtain energy by consuming organic moleculesmade by other organisms. Consumers can be grouped according tothe type of food they eat. Herbivores eat producers. An antelopethat eats grass is a herbivore. Carnivores eat other consumers.Lions, cobras, and praying mantises are examples of carnivores.Omnivores eat both producers and consumers. The grizzly bear,whose diet ranges from berries to salmon, is an omnivore.

Detritivores (dee-TRIET-uh-VAWRZ) are consumers that feed onthe “garbage” of an ecosystem. This waste, or detritus, includesorganisms that have recently died, fallen leaves, and animalwastes. The vulture shown in Figure 18-8 is a detritivore. Manybacteria and fungi are detritivores that cause decay by breakingdown complex molecules into simpler molecules. So, they arespecifically called decomposers. Some of the molecules releasedduring decay are absorbed by the decomposers, and some arereturned to the soil or water. Decomposers make the nutrientsthat were contained in detritus available again to the autotrophsin the ecosystem. Thus, the process of decomposition recycleschemical nutrients.

367

• Hearing Impaired • Learning Disabled • Developmentally Delayed • Attention Deficit Disorders • Behavior Control Issues

StrategiesStrategiesINCLUSIONINCLUSION

Because of their language delays, studentswho have hearing impairments, learningdisabilities, developmental delays, attention deficit disorders, and behaviorcontrol issues can benefit from methodsof learning input and output that do notinvolve language. One such method is toask students to interpret information inpictures. Have students draw or cut outpictures to make a poster of a specific

group of animals that are herbivores, carnivores, or omnivores, showing theanimals in their environment. For example,if herbivores are the topic, the postercould include caribou from the tundra or antelopes from the grasslands. Havestudents label each animal on the posterand title it by the group of organisms it represents.

ActivityObserving Plant DetritivoresCollect some leaf litter that hasbeen moist for some time. Placethe litter in dishes for observationunder dissecting microscopes.Have students observe the leaflitter for signs of mold. Ask themhow they can identify a mold andwhat role a mold plays in a forestecosystem. (Mold usually has a fuzzyappearance. Molds are detritivore in aforest ecosystem, breaking down leavesand other plant debris to organic mole-cules.) Ask them to which kingdommolds belong. (Most molds belong tothe kingdom Fungi.) Visual

Teaching TipUnderstanding Energy FlowHave students make a GraphicOrganizer similar to the one atthe bottom of this page that summarizes the flow of energyfrom producers to herbivores,omnivores, carnivores, anddetritivores. Visual

Using the FigureFood Webs Have students create a food web, as found inFigure 18-10, that might exist intheir schoolyard or in their ownyard. (Sample answer: Grass, trees,shrubs, weeds, and flowers are theproducers. Songbirds eat seeds, butsome also eat insects. The insects arealso eaten by lizards, which in turn arecaught by cats. Some insects eat otherinsects, and some feed on plants. Birdsmay be eaten by cats.) VisualLS

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368 C H A P T E R 1 8

ENERGY FLOWWhen one organism eats another, molecules are metabolized andenergy is transferred. As a result, energy flows through an ecosystem,moving from producers to consumers. One way to follow the patternof energy flow is to group organisms in an ecosystem based on howthey obtain energy. An organism’s trophic (TRAHF-ik) level indicatesthe organism’s position in a sequence of energy transfers. For exam-ple, all producers belong to the first trophic level. Herbivores belongto the second trophic level, and the predators belong to the thirdlevel. Most terrestrial ecosystems have only three or four trophic lev-els, whereas marine ecosystems often have more.

Food Chains and Food WebsA food chain is a single pathway of feeding relationships amongorganisms in an ecosystem that results in energy transfer. A foodchain may begin with grass, which is a primary producer. Thechain may continue with a consumer of grass seeds—a meadowmouse. Next, a carnivorous snake may kill and eat the mouse. Ahawk then may eat the snake, as shown in Figure 18-9.

The feeding relationships in an ecosystem are usually too com-plex to be represented by a single food chain. Many consumers eatmore than one type of food. In addition, more than one species ofconsumer may feed on the same organism. Many food chains inter-link, and a diagram of the feeding relationships among all theorganisms in an ecosystem would resemble a web, as shown inFigure 18-10. For this reason, the interrelated food chains in anecosystem are called a food web.

Hawk

Snake

Mouse

Grass

Energy is transferred from one organismto another in a food chain. The foodchain shown above begins with aproducer, grass, and ends with acarnivore, a hawk.

FIGURE 18-9

Because a large carnivore may be at thetop of several food chains, it is helpfulto show as many feeding relationshipsas possible in a food-web diagram.Not all organisms are listed in the foodweb. For example, no decomposers are shown.

FIGURE 18-10

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Graphic Organizer

Use this GraphicOrganizer withTeaching Tip:UnderstandingEnergy Flow onthis page.

Carnivores: consume herbivores

Omnivores: consume producers and herbivores

Detritivores: consume producers, herbivores, carnivores, and omnivores

Producers: makeenergy-storing

molecules

Herbivores: consume producers

TEACHER RESOURCES

Workbooks

Quick, Data, and Math Labs • Making a Food Web GENERAL

ReteachingFood Web Give students a pictureof a mouse, or place a picture onthe overhead. Have them con-struct a food web with as manyparts as possible that connect tothe mouse. Have students explaintheir food web to other students.

Visual

Quiz1.What is the organic material in

an ecosystem called? (biomass)

2.What is an organism called that eats both producers andconsumers? (an omnivore)

3.How much of the total energyis transferred from one trophiclevel to the next? (from� 1% to20%, averaging about 10%)

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Energy TransferFigure 18-11 represents the amount ofenergy stored as organic material ineach trophic level in an ecosystem.The pyramid shape of the diagramindicates the low percentage of energytransfer from one level to the next. Onaverage, 10 percent of the total energyconsumed in one trophic level is incor-porated into the organisms in the next.

Why is the percentage of energy transfer so low? One reason isthat some of the organisms in a trophic level escape being eaten.They eventually die and become food for decomposers, but theenergy contained in their bodies does not pass to a higher trophiclevel. Even when an organism is eaten, some of the molecules in itsbody will be in a form that the consumer cannot break down anduse. For example, a cougar cannot extract energy from the antlers,hooves, and hair of a deer. Also, the energy used by prey for cellu-lar respiration cannot be used by predators to synthesize new bio-mass. Finally, no transformation or transfer of energy is 100percent efficient. Every time energy is transformed, such as duringthe reactions of metabolism, some energy is lost as heat.

Limitations of Trophic LevelsThe low rate of energy transfer between trophic levels explainswhy ecosystems rarely contain more than a few trophic levels.Because only about 10 percent of the energy available at onetrophic level is transferred to the next trophic level, there is notenough energy in the top trophic level to support more levels.

Organisms at the lowest trophic level are usually much moreabundant than organisms at the highest level. In Africa, for exam-ple, you will see about 1,000 zebras, gazelles, and other herbivoresfor every lion or leopard you see, and there are far more grassesand shrubs than there are herbivores. Higher trophic levels con-tain less energy, so, they can support fewer individuals.

1. How do producers and consumers obtain energy?

2. Name five types of consumers.

3. What important role do decomposers play in anecosystem?

4. How does a food chain differ from a food web?

5. Give two reasons for the low rate of energytransfer within ecosystems.

6. Explain why food chains usually do not exceedthree to four levels.

CRITICAL THINKING

7. Predicting Results Describe the probableeffects on an ecosystem if all the plants were todie. What if all the decomposers were to die?

8. Evaluating Models A student has modeled anecosystem with seven trophic levels. Is this num-ber reasonable? Explain.

9. Analyzing Concepts Explain why the same areacan support a greater number of herbivores thancarnivores.

SECTION 3 REVIEW

This diagram represents energy transferthrough four trophic levels. The amountof energy transferred from one level toanother can vary, so the structure showncan vary. What is always true, however,is that the top level is much smallerthan the lowest level. Hence, energy-transfer diagrams are always roughlypyramid shaped.

FIGURE 18-11

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Small carnivores

Herbivores

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1. Producers convert energy from the sun or fromorganic molecules. Consumers obtain energy byeating other organisms.

2. herbivores, carnivores, omnivores, detritivores,and decomposers

3. They cause decay, releasing nutrients in organ-isms, and return the nutrients to the ecosystem.

4. Food chains show a single path of energy flow.Food webs show several paths of energy flow.

5. Many organisms avoid being eaten and the energyis partly lost, some of the molecules in a body areindigestible, and organisms use energy for theirown life processes.

6. About 10 percent of total energy is transferred fromone level to next, so there is not enough energyavailable to support more than a few trophic levels.

7. The ecosystem would collapse because plantsprovide energy to support all other organisms.If all decomposers died, other organisms woulddie because nutrients would not be recycled.

8. No, because in most cases, 90 percent of the energyfrom a trophic level is lost or used by animals atthat level, and thus, energy is not available to thenext higher level. Thus, terrestrial ecosystems usu-ally have only three or four levels because there isnot enough energy available for additional levels.

9. Only about 10% of the energy from herbivores istransferred to carnivores. So, an area can only sup-port about 10% as many carnivores as herbivores.

TEACHER RESOURCES

Technology

Transparencies• E4 Trophic Levels• E5 Food Chain in an Antarctic

Ecosystem• E6 Food Web in an Antarctic

Ecosystem• E7 Grassland Food Web• E8 Energy Transfer Through

Trophic Levels• E9 Four Trophic Levels in an

Aquatic Ecosystem• E10 Amount of Energy at

Four Trophic Levels• E11 Energy Efficiency in Food

Consumption

Visual Concepts CD-ROM• Food Chains and Food Webs,

Food Chains and Energy Transfer,Energy Pyramid

Science in Action

Review Answers

1. It was a mathematical model to predict the numberof species on an island. They theorized that smallerislands would have fewer species than larger ones,and that remote islands would have fewer speciesthan less remote islands.

2. Their model predicted that there would be 30 birdspecies on Krakatau. They found 27 species, sotheir prediction was very close.

3. Equilibrium might not be reached if the island had a violent geologic history, such as the frequent vol-canic eruptions on Krakatau. A hostile climatemight also prevent equilibrium from being reached.

370 C H A P T E R 1 8

HYPOTHESIS: The Number of Species on AnyIsland Is Constant

Ant biologist Edward O. Wilson (1929–) and mathe-matical ecologist Robert H. MacArthur (1930–1972)were both interested in community patterns withinnature. Shortly after they met, they decided to worktogether on a study of species on islands.

Wilson noticed that the number of ant species onan island correlate with the size of the island. Healso noticed that when a new ant species arrives onan island, one of the species already on the islandbecomes extinct. However, the total number of antspecies remains constant. Wilson and MacArthurhypothesized that islands have a constant numberof species. They proposed that the number of specieson an island reflects an equilibrium—a balancebetween the rate at which new species colonize theisland and the rate at which established speciesbecome extinct.

METHOD: Construct and Test a ModelMacArthur and Wilson developed a mathematicalmodel to explain their observations. The mathemat-ics of the theory is complex, but the broad outlinescenter on two observable patterns: (1) large islandshave more species than small islands have and (2)remote islands—those located far from the mainlandor from a larger island—have fewer species than lessremote ones.

MacArthur and Wilson decided to test their modelon Krakatau, an island in Indonesia on which a vol-cano had erupted in 1883, killing most forms of lifeon the island. The return of plant and animal lifeto the island had been carefully recorded sinceKrakatau was first revisited in 1886.

RESULTS: Species Reached EquilibriumAfter examining the records of bird life at Krakatau,they learned that the number of species had climbedto 27 before leveling off.

Science in Action

CONCLUSION: Prediction WasClose

Using their model, MacArthurand Wilson predicted that atthe point of equilibrium, thenumber of bird species wouldbe about 30. Their predictionhad come close.

Recent Tests of Island BiogeographyMore recent studies of islands, such as those in the Seaof Cortez, suggest that many models of island bio-geography may be required to explain patterns ofspecies distributions. Researchers have generatedalternative models that account for factors such asisland history, climate, and species interactions.

Robert H. MacArthur

Edward O. Wilson

When the volcano that forms the island of Krakatau erupted inthe 1880s, it destroyed most life on the island. As life returned,scientists had a unique opportunity to study ecology in action.

R E V I E W

1. Describe MacArthurand Wilson’s model ofisland biogeography.

2. Summarize theresults from testingthe model on Krakatau.

3. Critical ThinkingSuggest how island factors might prevent equilibriumfrom being reached in MacArthur and Wilson’s model.

Testing a Theory of BiogeographyIn the 1960s, mathematical ecologist Robert H. MacArthur ofPrinceton University and taxonomist Edward O. Wilson of HarvardUniversity developed a theory and mathematical model of island bio-geography based on their study of species on islands. This model, andothers inspired by it, is used to explain patterns of species distributionaround the world.

www.scilinks.org

Topic: Island BiogeographyKeyword: HM61693

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BackgroundEdward O. Wilson earned his doctorate atHarvard University in 1955. He is recog-nized today as the world’s leading authorityon ants. The late Robert H. MacArthur, aprofessor of biology at Princeton University,was the ecologist who developed the categories of “r” and “K” to describe thelife and reproductive strategies of speciesand who first described the niche strategyof resource partitioning.

Biogeography is the study of the geo-graphic distribution of plants and animalsin an area. Wilson and MacArthur realizedthat islands offer a controlled area forstudying the factors that affect species’distribution. Their theory of island bio-geography predicts the number of speciesthat can inhabit an island.

DiscussionGuide the discussion by posing the following questions:

1.What two observations form the basisof MacArthur and Wilson’s theory ofisland biogeography? (Large islandshold more species than small islands.Remote islands have fewer speciesthan less remote islands.)

2.MacArthur and Wilson used their theoryto predict the number of bird specieson the island of Krakatau. How closewas their prediction? (They predictedthe number of bird species would be30. They found 27 species.)

3.Why did they use the term equilibriumto refer to the constant number ofisland species? (to refer to the stableor balanced state of the number ofspecies)

Testing a Theory of Biogeography

OverviewBefore beginning this section,review with students the Objectives listed in the StudentEdition. This section describesthe predictable patterns of water,carbon, nitrogen, and phosphoruscycles in an ecosystem. This section also emphasizes how the stability of biogeochemicalcycles may be disrupted byhuman activities.

Ask students which items theyuse can be recycled. Compile alist of recyclable items on theboard. Ask students to list thebenefits and problems with recy-cling things such as glass bottles,aluminum cans, and paper.

Intrapersonal

DiscussionDrinking Water Ask studentswhere they think their drinkingwater comes from. (probably fromeither a reservoir or wells) Then, askstudents how the local drinkingwater could become polluted.(Sample answers: by industry dischargingwastes or chemicals into streams orfrom runoff from lawns and fields)

Logical

Word Origins The water cycle issometimes called the hydrologiccycle. Have students research theorigin of the word hydrologic. (fromthe Greek hydro, meaning “water” andthe Latin logia,meaning “study of.”) Askstudents to list other words thatbegin with hydro. (hydrology,hydroponics, andhydroplane) Verbal LS

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Water vapor(clouds)

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EvaporationEvaporation

E C O S YS T E M R E C YC L I N GAs energy and matter flow through an ecosystem, matter must

be recycled and reused. Substances such as water, carbon,

nitrogen, calcium, and phosphorus each pass between the living

and nonliving worlds through biogeochemical cycles.

THE WATER CYCLEWater is crucial to life. Cells contain 70 to 90 percent water, andwater provides the environment in which most of life’s chemicalreactions occur. The availability of water is one of the key factorsthat regulate the productivity of terrestrial ecosystems. However,very little of the available water on Earth is trapped within livingthings at any given time. Bodies of water, such as lakes, rivers,streams, and oceans, contain a substantial percentage of Earth’swater. The atmosphere also contains water—in the form of watervapor. In addition, some water is found below ground. Water in thesoil or in underground formations of porous rock is known asgroundwater.

The movement of water between these various reservoirs,known as the water cycle, is illustrated in Figure 18-12. Threeimportant processes in the water cycle are evaporation, transpira-tion, and precipitation.

SECTION 4

O B J E C T I V E S

● List four major biogeochemicalcycles.

● Summarize three importantprocesses in the water cycle.

● Outline the major steps in thecarbon cycle.

● Describe the role of decomposersin the nitrogen cycle.

● Summarize the major steps of thephosphorus cycle.

V O C A B U L A R Y

biogeochemical cyclegroundwaterwater cycletranspirationcarbon cyclenitrogen cyclenitrogen fixationnitrogen-fixing bacteriaammonificationnitrificationdenitrificationphosphorus cycle

In the water cycle, water falls to Earth’ssurface as precipitation. Some waterreenters the atmosphere by evaporationand transpiration. Some water runs intostreams, lakes, rivers, and oceans. Otherwater seeps through the soil andbecomes groundwater. Follow thepathways of the water cycle in the figure.

FIGURE 18-12

371

SECTION 4

TEACHER RESOURCES

Workbooks


Technology

Transparencies• E12 Water Cycle• E13 Carbon Cycle• E14 Nitrogen Cycle

Visual Concepts CD-ROM• Biogeochemical Cycle, Water Cycle,

Groundwater, Water Table, Carbon Cycle, Nitrogen Cycle, Nitrogen Fixation, Ammonification, Nitrification, Denitrification

Modeling GroundwaterTime Required 25 minutes

Safety safety goggles, apron, disposable gloves

Procedural Tips Have studentswork in teams of three or four.Each team will need a plastic sodabottle prepared ahead of time.Punch several small holes aroundthe neck of the bottle and in thebottle cap. Use a large nail and ahammer to punch the holes. Cutthe bottle in half. Obtain squaresof sod from a nursery, or get per-mission to dig grassy soil from alocal area. The sod must be dry.

Answers to Analysis Answers may varyaccording to the type of soil used. Thewater will take longer to drain throughclay soil, but it will drain quickly throughsandy soil. Clay will hold the most water,and sand will hold the least amount of water. Loamy garden soil will holdapproximately 100 mL of water. In nature,the water will drain through the soil downto the groundwater where dissolved fertilizer or pesticides might contaminatethe groundwater.

Teach

Trends in ClimatologyThe Greenhouse Effect and Carbon DioxideClimatologists have calculated that the meanglobal temperature has increased about 1°Csince 1900. The U.S. National Research Councilrecently estimated that by the year 2035, theaverage surface air temperature will increasebetween 1.5°C and 4.5°C. It was also suggestedthat the increase might be much greaterbecause of the number of trace gases, suchas methane, nitrous oxide, ozone, and chlorofluorocarbons, which are increasingrapidly and have warming or greenhouseeffects similar to those of carbon dioxide.

372 C H A P T E R 1 8

Evaporation adds water as vapor to the atmosphere. Heatcauses water to evaporate from bodies of water, from the soil, andfrom the bodies of living things. The process by which water evap-orates from the leaves of plants in terrestrial ecosystems is calledtranspiration. Transpiration causes plants to take in water throughtheir roots to replace the water that is being lost through theirleaves. Animals also participate in the water cycle. Animals drinkwater or obtain it from their food. They release this water whenthey breathe, sweat, or excrete.

Water leaves the atmosphere through precipitation. The amountof water the atmosphere can hold depends on abiotic factors, suchas temperature and air pressure. Once the atmosphere becomessaturated with water vapor, precipitation occurs in the form ofrain, snow, sleet, hail, or fog.

THE CARBON CYCLEPhotosynthesis and cellular respiration form the basis of the short-term carbon cycle, illustrated in Figure 18-13. In photosynthesis,plants and other autotrophs use carbon dioxide (CO2), along withwater and solar energy, to make carbohydrates. Both autotrophsand heterotrophs use oxygen to break down carbohydrates duringcellular respiration. The byproducts of cellular respiration are car-bon dioxide and water. Decomposers release carbon dioxide intothe atmosphere when they break down organic compounds.

Carbon exists in the atmosphere ascarbon dioxide. Cellular respiration,combustion, and decomposition oforganic matter are the three majorsources of carbon dioxide in the short-term carbon cycle. By burning largeamounts of fossil fuels, humans arereleasing carbon dioxide from a long-term reservoir and increasing theamount of carbon dioxide in theatmosphere.

FIGURE 18-13

Modeling Groundwater

Materials disposable gloves, labapron, 3 L plastic bottle (cut inhalf), small stones (250 mL), dry sodwith grass, water, graduated cylin-der, 500 mL beaker

Procedure1. Put on your lab apron, goggles,

and disposable gloves.

2. Invert the top half of the plasticbottle, and place it inside thebottom half of the bottle to forma column.

3. Place the stones in the bottomof the inverted top half of thebottle. Place a chunk of dry sodwith grass on top of the stones.

4. Pour 250 mL of water over thesod, and observe how the waterpenetrates the soil and movesthrough the column.

5. When the water is no longerdraining, remove the top half ofthe column, and pour the waterfrom the bottom of the columninto a beaker. Measure the vol-ume of liquid in the beaker.

Analysis What is the volume ofthe water that drained throughthe sod? How much of the waterremained in the soil? Where doesthe water go when applied to a reallawn or crop? What might the fateof fertilizer or pesticides be that areapplied to a lawn or crop?

Quick Lab

Cellularrespiration

Combustion

Photosynthesis

Fossilfuels

Carbon dioxidein atmosphere

Death anddecomposition

Fossilfuels

372

CHEMISTRYCHEMISTRYCONNECTIONCONNECTION

Carbon Chemistry The most common ele-ments in living things are carbon, hydrogen,oxygen, and nitrogen. The bonding ofhydrogen, nitrogen, oxygen, and other elements with carbon forms organic molecules. Carbon-based organic mole-cules often form long chains. These chainsof molecules form carbohydrates, fats,amino acids, nucleic acids, and proteinswithin living organisms.

TEACHER RESOURCES

Workbooks

Datasheets for In-Text Labs• Modeling Groundwater

Forensics Labs• Solubility and Chemical Fertilizers

GENERAL

DiscussionMarine Links to the CarbonCycle Discuss the role of marineorganisms in the carbon cycle.Tell students that coral organismsbuild reefs of calcium carbonatethat contain carbon. The carboncomes from food produced byphotosynthetic algae that liveinside the coral. Other organisms,such as many mollusks, producea calcium carbonate shell. Whenthese animals die, their shellsbecome part of the bottom sedi-ment that may eventually becomelayers of rock. The calcium car-bonate eventually decomposes tocarbon dioxide and calcium oxide.The carbon dioxide is releasedinto the atmosphere. Auditory

Cycles of Matter Have studentsresearch the different cycles ofmatter by using the Internet Connect box on this page.

Intrapersonal

Using the FigureNitrogen Cycle Point out inFigure 18-14 that the nitrogencycle depends on bacteria fornitrogen conversion. Ask stu-dents how human activities coulddisrupt this cycle. (The addition oftoxic chemicals to soil or the use of pesticides and herbicides may alter thebacterial composition of soil. Constructionand deforestation also cause soil erosionthat could eliminate soil bacteria.)

Logical

Teaching TipThe Greenhouse Effect andMethane The atmospheric levelof methane has more than doubledsince 1951. Ask students what hascaused this increase in atmos-pheric methane. (Methane is a prod-uct of the bacterial decomposition oforganic matter in the absence of oxygen.This decomposing action has occurredmainly in rice paddies and in the diges-tive tracts of termites, which are nowpresent in greater numbers because ofall the forests that are being destroyed.Students may be amused to learn thatbelching by cattle and sheep is anothersource of greenhouse gases.) LogicalLS

GENERAL

LS

GENERAL

LS

GENERAL

LS

GENERAL


Assimilation Nitrogenfixation

Nitrogen-fixingbacteria inplant roots

Nitrogen-fixingbacteria in soil

Nitrifyingbacteria

Denitrifyingbacteria

Atmosphericnitrogen (N2)

Animals

Death Death

Plants

Ammonia (NH3) and Ammonium (NH4+)

Nitrates(NO3)

Waste(urine and feces)

Decomposers

Denitrification

Nitrification Nitrogenfixation

Ammonification

Human Influences on the Carbon CycleIn the last 150 years, the concentration of atmospheric carbondioxide has risen more than 30 percent. Humans contribute to thisincrease by burning fossil fuels and other organic matter. Ourindustrial society depends on the energy released by the burningof fossil fuels—coal, oil, and natural gas. Fossil fuels are theremains of organisms that have been transformed by decay, heat,and pressure into energy-rich molecules. Burning releases theenergy in these molecules, but it also releases carbon dioxide.When large areas of forest are burned each year to clear land foragriculture, less vegetation remains to absorb carbon dioxide fromthe atmosphere through photosynthesis.

NITROGEN CYCLEAll organisms need nitrogen to make proteins and nucleic acids.The complex pathway that nitrogen follows in an ecosystem iscalled the nitrogen cycle, as shown in Figure 18-14. Nitrogen gas,N2, makes up about 78 percent of the atmosphere, so it might seemthat it would be readily available for living things. However, mostplants can use nitrogen only in the form of nitrate. The process ofconverting N2 gas to nitrate is called nitrogen fixation.

Most organisms rely on nitrogen-fixing bacteria to transformnitrogen gas into a usable form. These bacteria live in the soil andinside swellings on the roots of some kinds of plants, such asbeans, peas, clover, and alfalfa. These plants supply carbohydratesfor the bacteria, and the bacteria produce usable nitrogen for theplant. Additional nitrogen is released into the soil.

This figure shows the cycling of nitrogenwithin a terrestrial ecosystem. Bacteriaare responsible for many of the stepsin the nitrogen cycle, including theconversion of atmospheric nitrogen intoammonium. Nitrogen-fixing bacteria livein the soil or in the roots of plants. Thesebacteria convert nitrogen gas intoammonium. Other bacteria convert theammonium into nitrates. Plants take upthe nitrates produced by the bacteria.Animals get nitrogen by eating plantsor other animals.

FIGURE 18-14

www.scilinks.org

Topic: Cycles of MatterKeyword: HM60373

373

• Developmentally Delayed • Attention Deficit Disorders • Behavior Control IssuesStrategiesStrategiesINCLUSIONINCLUSION

Students who have developmental delays,attention deficit disorders, or behaviorcontrol issues often have little understand-ing of ideas until they can connect the ideasto themselves. If they are able to visualizethemselves in a situation that illustrates an idea, they are more able to have a clearunderstanding of the idea. After studentsread this section, take students on a walkaround the campus to point out various

examples of the carbon, nitrogen, andwater cycles. If the school grounds havegrass, point out that fertilizers may be usedto make it grow, and show students wherethe fertilizers might run off. If a stream,pond, or gutter is nearby, have studentsspeculate on where the water goes andhow it relates to the water cycle. Have stu-dents discuss their observations in class.

ReteachingPlants and BiogeochemicalCycles Have students write ashort essay on how plants areimportant in biogeochemical cycle.(Water passes through plants in theprocess of transpiration. Plants use carbondioxide (CO2) to make carbohydrates.Leguminous plants contain nitrogen-fixingbacteria that transform nitrogen gas intoa usable form in living organisms. Plantsget phosphorus from soil and water, andanimals get phosphorus by eating plants.)

Verbal

Quiz1.What biogeochemical cycles is

photosynthesis part of? (the water cycle and the carbon cycle)

2.What process returns nitrogento the atmosphere? (denitrification)

3.How do plants and animalsobtain phosphorus? (plants:from water and through their roots,and animals: from eating plants orother animals)

GENERAL

LS

Close


1. water, nitrogen, carbon, phosphorus2. evaporation3. Photosynthesis uses atmospheric CO2 to build

organic molecules. Cellular respiration, combustion,and decomposition release CO2 to the atmosphere.

4. They break down the nitrogen-containing moleculesin dead organisms and wastes and make nitrogenavailable to other organisms.

5. erosion of rocks into the soil and water,decomposition of organisms, and fertilizers

6. It might eliminate the plants that produce oxygenand lower oxygen levels in the atmosphere.

7. carbon: bacteria take in CO2 during photosynthesisand release CO2 during cellular respiration;.nitrogen: bacteria can take in nitrogen gas fromthe atmosphere and convert it to ammonium,or convert ammonium into nitrites and nitrates;phosphorus: bacteria break down wastes anddead organisms to release carbon and nitrogen

8. Nutrients cycle because they can be used overand over by organisms as they move through theecosystem, whereas most energy flows in onedirection and is used up or lost as it flows througha food chain.

374 C H A P T E R 1 8

1. Identify four major biogeochemical cycles.

2. Through what process does most water vaporenter the atmosphere?

3. Outline the steps of the carbon cycle.

4. Describe the role of decomposers in thenitrogen cycle.

5. Identify the sources of phosphorus in thephosphorus cycle.

CRITICAL THINKING

6. Inferring Relationships How might the removal of vegetation affect oxygen levels inthe atmosphere?

7. Making Comparisons Identify the role of bacte-ria in the carbon, nitrogen, and phosphorus cycles.

8. Analyzing Concepts Explain the statement thatnutrients cycle, but energy flows.

SECTION 4 REVIEW

Recycling NitrogenThe bodies of dead organisms contain nitrogen, mainly in proteinsand nucleic acids. Urine and dung also contain nitrogen.Decomposers break down these materials and release the nitrogenthey contain as ammonia, NH3, which in soil becomes ammonium,NH4

�. This process is known as ammonification. Through thisprocess, nitrogen is again made available to other organisms.

Soil bacteria take up ammonium and oxidize it into nitrites,NO2

�, and nitrates, NO3�, in a process called nitrification. The ero-

sion of nitrate-rich rocks also releases nitrates into an ecosystem.Plants use nitrates to form amino acids. Nitrogen is returned to theatmosphere through denitrification. Denitrification occurs whenanaerobic bacteria break down nitrates and release nitrogen gasinto the atmosphere. Plants can absorb nitrates from the soil, butanimals cannot. Animals obtain nitrogen in the same way theyobtain energy—by eating plants and other organisms and thendigesting the proteins and nucleic acids.

PHOSPHORUS CYCLEPhosphorus is an element that is an essential material needed byanimals to form bones, teeth, and parts of molecules, such as DNAand RNA. Plants get the phosphorus they need from soil and water,whereas animals get their phosphorus by eating plants or otheranimals. The phosphorus cycle is the movement of phosphorusfrom the environment to organisms and then back to the environ-ment. This cycle is slow and does not normally occur in the atmos-phere, because phosphorus rarely occurs as a gas.

When rocks erode, small amounts of phosphorus dissolve asphosphate, PO4

3�, in soil and water. Plants absorb phosphorus inthe soil through their roots. Phosphorus is also added to soil andwater when excess phosphorus is excreted in wastes from organ-isms and when organisms die and decompose. Some phosphorusapplied to fields as fertilizer washes off the land into streams andgroundwater.

374

AlternativeAssessmentBiogeochemical Cycles Havestudents select one of the fourbiogeochemical cycles discussedin the chapter. Have the studentsconstruct a poster or multimediapresentation explaining the cyclethey have chosen. Students can then present their work tothe class. Visual

Study TipReading Effectively Make surestudents use the section Objectivesand subheadings as they read tohelp them identify the main ideas.

VerbalLS

GENERAL

Co-op LearningLS

GENERAL


Introduction to EcologySECTION 1

CHAPTER HIGHLIGHTS

ecology (p. 359)interdependence (p. 359)

ecological model (p. 360)biosphere (p. 361)

ecosystem (p. 362)community (p. 362)

population (p. 362)Vocabulary

habitat (p. 363)biotic factor (p. 363)abiotic factor (p. 363)

tolerance curve (p. 363)acclimation (p. 364)dormancy (p. 365)

migration (p. 365)niche (p. 365)

Vocabulary

biogeochemical cycle (p. 371)groundwater (p. 371)water cycle (p. 371)transpiration (p. 372)

carbon cycle (p. 372)nitrogen cycle (p. 373)nitrogen fixation (p. 373)

nitrogen-fixing bacteria (p. 373)

ammonification (p. 374)

nitrification (p. 374)denitrification (p. 374)phosphorus cycle (p. 374)

Vocabulary

producer (p. 366)chemosynthesis (p. 366)gross primary

productivity (p. 366)

biomass (p. 366)net primary

productivity (p. 366)consumer (p. 367)

herbivore (p. 367)carnivore (p. 367)omnivore (p. 367)detritivore (p. 367)

decomposer (p. 367)trophic level (p. 368)food chain (p. 368)food web (p. 368)

Vocabulary

● Species interact with both other species and theirnonliving environment.

● Interdependence is a theme in ecology, and states thatone change can affect all species in an ecosystem.

● Ecological models help to explain the environment.● Ecology is usually organized into five levels: organism,

population, community, ecosystem, and biosphere.

Ecology of OrganismsSECTION 2

● Both biotic, or living, factors and abiotic, or nonliving,factors influence organisms. Examples of nonliving thingsare climate, sunlight, and pH.

● A niche is a way of life, or a role in an ecosystem.● Some species survive unfavorable environmental

conditions by becoming dormant or by migrating.

Energy TransferSECTION 3

● Most producers are photosynthetic and makecarbohydrates by using energy from the sun.

● Consumers obtain energy by eating other organisms andinclude herbivores, omnivores, carnivores, detritivores,and decomposers.

● Decomposers feed on dead organisms and wastes, whichreleases the nutrients back into the environment.

● A single pathway of energy transfer is a food chain.A network showing all paths of energy transfer is a food web.

● Ecosystems contain only a few trophic levels becausethere is a low rate of energy transfer between each level.

Ecosystem RecyclingSECTION 4

● Key processes in the water cycle are evaporation,transpiration, and precipitation.

● Photosynthesis and cellular respiration are the two mainsteps in the carbon cycle.

● Nitrogen-fixing bacteria are important in the nitrogencycle because they change nitrogen gas into a usableform of nitrogen for plants.

● Phosphorus moves from phosphate deposited in rock, tothe soil, to living organisms, and finally to the ocean.

375

Answer to Concept Map

The following is one possible answerto Chapter Review item 22.

SECTION 0CHAPTER HIGHLIGHTS

TEACHER RESOURCES

Workbooks

• Study Guide• Vocabulary Review• Science Skills• Critical Thinking• Quizzes• Chapter Test• Chapter Test

Technology

Transparencies• Graphic Organizer• Concept Mapping

One-Stop Planner CD-ROM• Concept Mapping

Worksheet GENERAL

GENERAL

GENERAL

GENERAL

GENERAL

GENERAL

Water

precipitation

when it fallsto earth

undergoes

transpiration

when it is released by plants

as water vapor

evaporation

as water vaporinto the

atmosphere

water vapor is then condensedinto a liquid through

condensation

ANSWERS

Using Vocabulary1. a. regulators use energy to control

some internal conditions; conformerschange as their external environmentchanges b. ecosystem includes bothliving and nonliving things in one place;community is different species oforganisms in an area c. migration: whenanimals escape from unfavorableconditions by moving; dormancy:organisms escape by becominginactive d. nitrogen fixation: produc-tion of ammonium from atmosphericnitrogen; ammonification: release ofammonia as a result of decomposition

2. Sample answer: Consumers, such asherbivores, omnivores, carnivores,decomposers, and detritivores, eatproducers, other consumers, or wastematerials.

3. In transpiration, plants “breathe” byhaving leaves release water and oxy-gen, and take in carbon dioxide (CO2)through the same pores.This is meta-phorically like breathing in animals.

Understanding Key Concepts4. Small changes in the environment

through interdependence canincrease certain environmental fac-tors that cause disease.

5. Models help ecologists simplify andunderstand complex ecosystems.

6. Models may be too simplified and notaccount for the influences of all factors.

7. biosphere, ecosystem, community,population, organism

8. abiotic: temperature and sunlight;biotic: predators and plants availablefor food

9. an organism’s role in the environmentincluding its way of getting resources,range of conditions tolerated, offspringnumber, time of reproduction, andall other interactions between theorganism and its environment

10. Conformers can’t regulate their internal conditions,so they change with the environment or migrate.Regulators use energy to control some of their inter-nal conditions and function over a wider range ofconditions than conformers.

11. photosynthetic: use the sun’s energy to makeorganic molecules; non-photosynthetic: useenergy from inorganic molecules

12. Herbivores eat producers, carnivores eat herbi-vores or other carnivores, and omnivores eatboth producers and other consumers.

13. herbivores: deer, grasshopper; carnivores: cougars,hawks; omnivores: humans, raccoons

14. They break down molecules in dead tissues andwastes and return nutrients to the environment.

15. A food chain has only one path of energy transfer.Most organisms feed on more than one type offood, so the actual energy path is like a web.

16. Only 10 % of the total energy consumed in one levelis incorporated into the next level. Thus, there isonly enough energy to support a few levels.

17. Energy flows from producers to consumers andsome energy is used at each level. Nutrients cyclewithin an ecosystem and can be used again.

18. Plants release water to the atmosphere bytranspiration through their leaves.

19. CO2 is used by producers during photosynthesis,and is released by respiration, burning of fossilfuels and plants, and decomposition.

376 C H A P T E R 1 8

CHAPTER REVIEW

USING VOCABULARY1. For each pair of terms, explain how the meanings

of the terms differ.a. conformer and regulatorb. community and ecosystemc. migration and dormancyd. nitrogen fixation and ammonification

2. Use the following terms in the same sentence:producer, consumer, herbivore, omnivore,carnivore, detritivore, and decomposer.

3. Word Roots and Origins The word transpirationis derived from the Latin trans, which means“through,” and spirare, which means “breathe.”Using this information, explain why the termtranspiration is a good name for the process itdescribes.

UNDERSTANDING KEY CONCEPTS4. Explain how an understanding of interdepen-

dence in ecosystems might be important topublic health officials.

5. Evaluate how models are valuable to ecologists.

6. Describe some limitations of ecological models.

7. Identify five levels of organization in ecology.

8. Propose two examples of biotic factors andabiotic factors.

9. Explain the ecological concept of a niche.

10. Distinguish between conformers and regulators inhow they deal with environmental change.

11. Compare photosynthetic and nonphotosyntheticproducers.

12. Distinguish between a herbivore, a carnivore, andan omnivore.

13. State an example of each of the following: aherbivore, a carnivore, and an omnivore.

14. Explain the importance of decomposers in anecosystem.

15. Describe why a food web is a more complete pic-ture of the feeding relationships in an ecosystemthan a food chain is.

16. Identify the reasons why most ecosystems nor-mally contain only a few trophic levels.

17. Compare the transfer of energy with the transferof nutrients in an ecosystem.

18. Explain how plants return water to the atmos-phere as part of the water cycle.

19. Describe two processes in the carbon cycle.

20. List the mutual benefits in the associationbetween nitrogen-fixing bacteria and the plantsthat they inhabit.

21. Summarize the phosphorus cycle.

22. CONCEPT MAPPING Use the following terms to create a concept map that

shows some of the processes involved in thewater cycle: evaporation, precipitation,transpiration, and condensation.

CRITICAL THINKING23. Interpreting Graphics Examine the diagram below

of a tolerance curve. Briefly describe the condi-tions in each zone of tolerance and the reactionsa species may have to them.

24. Relating Concepts Nitrogen, water, phosphorus,and carbon are recycled and reused within anecosystem, but energy is not. Explain why energycannot be recycled.

25. Drawing Conclusions In the fall, many kinds ofsongbirds migrate from the United States toCentral America or South America. Explain thebenefits of migration for songbirds. What aresome possible costs of this behavior?

26. Analyzing Concepts Ecologists have identifiedseveral characteristics that increase the likeli-hood that a species will become extinct.Specialization is one such characteristic. Explainwhy a very specialized species is likely to bemore vulnerable to extinction.

27. Making Models Farmers often grow alfalfa, clover,or bean plants in fields after they have grown a grain crop. Explain this practice in terms ofbiochemistry.

Low salinity High salinity

Intolerance IntoleranceStress StressOptimal

Salinity Tolerance Curve

Tolerancelimit

Oxy

gen

con

sum

pti

on

Tolerancelimit

376

CHAPTER REVIEW

ANSWERS


Standardized Test PreparationDIRECTIONS: Choose the letter of the answer choicethat best answers the question.

1. What are the levels of organization in ecology?A. cell, tissue, organ, organ system, bodyB. organ, organism, population, communityC. organism, population, community, ecosys-

tem, biosphereD. population, habitat, ecosystem, biogeochem-

ical system, planet

2. What makes up an ecosystem?F. all the habitat types on EarthG. all parts of Earth where life existsH. all members of a species in the same areaJ. all the living and nonliving factors in an

environment

3. Which of the following are abiotic factors?A. plantsB. animalsC. sunlightD. microorganisms

4. How do decomposers benefit an ecosystem?F. by returning nutrients to the soilG. by manufacturing energy from sunlightH. by removing excess nutrients from the soilJ. by removing predators from the ecosystem

5. Which organisms are most critical in the nitrogencycle?A. plantsB. nitratesC. animalsD. bacteria

INTERPRETING GRAPHICS: The illustration below rep-resents a trophic pyramid. Use the illustration toanswer the question that follows.

6. What is the term for the kinds of organisms thatmake up the trophic level labeled C?F. producersG. consumersH. detritivoresJ. decomposers

DIRECTIONS: Complete the following analogy.

7. bear : omnivore :: vulture :A. producerB. herbivoreC. detritivoreD. decomposer

INTERPRETING GRAPHICS: The illustration belowrepresents a food chain. Use the illustration toanswer the questions that follow.

8. What role do the krill have in this food chain?F. They are producers.G. They are consumers.H. They are detritivores.J. They are decomposers.

SHORT RESPONSEGive two reasons why the destruction of tropical rainforests can contribute to an increase in carbon diox-ide levels in the atmosphere.

EXTENDED RESPONSESome species are generalized with regard to theirniche, and other species are specialized.

Part A Compare the niche of a generalist specieswith one of a specialist species.

Part B Predict how two different herbivores canshare the same plant resource.

If you are not sure about thespelling of certain words when answering the short or extended response questions, look at the questionitself to see if the same word appears in the question.

Killer whale

Leopard seal

Cod

Krill

Algae

eagle

snake

rat

plant

D

C

B

A

377

20. bacteria get a place to live and sugars from plant;plants get a usable form of nitrogen from thebacteria

21. Phosphorus in rocks is eroded and washed intothe soil and water along with phosphorus fromfertilizer. Plants absorb it through their roots fromthe soil. Decomposition returns phosphorus to thesoil and water.

22. The answer to the concept map is found at thebottom of the Chapter Highlights page.

Critical Thinking23. optimal: species functions best, all requirements

are met; stress: at least one factor is not optimal,species can survive but not at its best level;

intolerance: species meets stressful conditionsin at least one factor, survival is threatened; out-side the tolerance limit: species can’t survive

24. At each level, energy is dissipated as heat, a formof energy organisms can’t use. Thus, energy iscontinually “lost” to the ecosystem.

25. By migrating, birds escape the extreme cold andfood shortages of winter. Migration costs a largeamount of energy from flying long distances.

26. A specialized species requires a narrow rangeof environmental conditions and resources. Sucha species is vulnerable to changes that shiftconditions outside its tolerance range.

27. These legume plants harbor nitrogen-fixingbacteria and thus release nitrogen to the soil.

SECTION 0Standardized TestPreparation

Teaching TipTo provide practice under realistic test-ing conditions, give students 20 minutesto answer the Standardized TestPreparation questions.

1. C2. J3. C4. F5. D6. G7. C8. G

Short ResponseThe burning of vegetation releases CO2into the atmosphere and removes plants that could have absorbed atmospheric CO2.

Extended ResponsePart A Generalist species have a broad

niche, as they can tolerate a widerange of conditions and use a widevariety of resources. Specialistspecies can use only specificresources and have more narrowlydefined niches.

Part B Two herbivores might eat differ-ent parts of the plant, or they mighteat the plant at different times of the year.

Question 1 Students may chooseAnswer D if they do not read the answersvery carefully. Answer D also containsterms that are related to ecology, butthey are not all levels of organization.The correct answer is C. Remind stu-dents to take their time and read all theanswers carefully.

EXPLORATION LAB

Time RequiredTwo 50-minute lab periods

Ratings

TEACHER PREPARATION

STUDENT SETUP

CONCEPT LEVEL

CLEANUP

Safety CautionsRemind students that they are workingwith live animals and should treatthem gently.

PreparationOrder brine shrimp in advance from abiological supply house. Allow extratime to grow large cultures.

Materials and EquipmentUse the Lab Materials QuicklistSoftware on the Biology LabGenerator CD-ROM to create a customized list of materials for this lab.

Procedural Tips1. Use 0.5 in. internal diameter plastic

tubing cut into 44 cm lengths. Whentubing is divided as directed, it allowsfor space taken up by stoppers andforms equal quarters.

2. Detain™ microlife slowing agentworks well to slow the movementof brine shrimp without killingthem. You may substitute methylcellulose, which does not work as well.

E A SY HAR D

3. For the reaction to light, soft-white fluorescentbulbs are recommended.These bulbs will give sufficient light without significantly changing thetemperature. Grow lights will also work well, andeven natural lighting is acceptable. Avoid incan-descent bulbs, which pose the hazard of burns.

4. Fiberglass screening is available at hardwarestores or may be ordered from a biological supply house.

5. Divide the class into teams of six, with two stu-dents in each team working on each part (A, B, or C).

6. Students may count shrimp by viewing them in the Petri dish or by holding the pipet up to the light.

7. Dispose of broken glass in the designated wastecontainer. Dispose of the brine shrimp according to the directions provided by the biological supplyhouse that you purchased them from. Do not pourchemicals down the drain.

378 C H A P T E R 1 8

Observing Habitat Selection

■ Assess the effect of light on habitat selection by brineshrimp.

■ safety goggles■ lab apron■ protective gloves■ marking pen■ clear, flexible plastic tubing (44 cm long)■ 4 test tubes with stoppers■ test-tube rack■ 2 corks to fit tubing■ graduated cylinder■ funnel■ brine shrimp culture■ aluminum foil■ 3 screw clamps■ 1 pipet■ Petri dish■ methyl cellulose■ fluorescent lamp or grow light■ 14 pieces of screen or thin cloth■ calculator

Background

1. Recall that a species’ habitat is a specific areawhere it lives.

2. A species habitat selection depends on how well thelocation fits within the species’ tolerance range. Themore optimal all limiting factors are within a por-tion of an organism’s range, the more likely theorganism is to select that area for its habitat.

3. What limiting factors might be involved in habitatselection?

4. What is a niche?

Setting Up

1. Put on safety goggles, a labapron, and protective gloves.

Mark the plastic tubing at 12 cm, 22 cm, and 32 cmfrom one end so that you will have the tube dividedinto four sections. Starting at one end, label the sec-tions 1, 2, 3, and 4. Label four test tubes 1, 2, 3, and 4.

2. Place a cork in one end of the tubing. Use a gradu-ated cylinder and a funnel to transfer about 50 mLof brine shrimp culture into the tubing. Cork theopen end, and lay the tubing on the desktop.

3. You and your partner will complete either PartB or Part C and then share your results with

the other students on your team. CAUTION You willbe working with live animals. Be sure to treatthem gently and to follow directions carefully.

Control Group

1. Cover the tubing with aluminum foil, and let itremain undisturbed for 30 minutes. While you arewaiting, create a data table like Table A, below, inyour lab report to record the numbers of shrimp ineach section of the tubing.

2. After 30 minutes have passed, attach screw clamps toeach spot that you marked on the tubing. While yourpartner holds the corks firmly in place, tighten themiddle clamp first, and then tighten the outer clamps.

3. Immediately pour the contents of each section oftubing into the test tube labeled with the corre-sponding number.

PART B

PART A

SAFETY

MATERIALS

OBJECTIVES

EXPLORATION LAB

TABLE A CONTROL GROUP

AverageTest number oftube Count Count Count Count Count shrimp innumber 1 2 3 4 5 test tube

1

2

3

4

378

Answers to Analysis and Conclusions

1. Answers may vary, depending on the species of Artemia used. Eachgroup’s histograms will be different,but they should see similar differ-ences between the control and experimental groups.

2. The control was necessary to showthat the brine shrimp did not inherentlyprefer one part of the tube—the endsor the middle, for example.

3. Answers may vary, depending on thespecies of Artemia used.

Answers to Further InquiryDesigns may vary but should includesubjecting the brine shrimp to tempera-ture extremes and should include amethod of eliminating all other variables,such as placing all test animals underthe same light level.


4. CAUTION If you get methyl cellulose in youreyes, immediately flush it out at the eyewash

station while calling to your teacher. Stopper testtube 1, and invert it gently to distribute the shrimp.Use a pipet to draw a 1 mL sample of shrimp cultureand transfer the culture to a Petri dish. Add a fewdrops of methyl cellulose to the Petri dish to slowdown the shrimp. Count the live shrimp, and recordthe count in your lab report.

5. Dispose of the shrimp as your teacher directs.Repeat step 4 four more times for a total of five

counts from test tube 1.6. Calculate the average number of shrimp in test tube 1,

and record the result in the data table you made inyour lab report.

7. Repeat steps 4–6 for the contents of each of theremaining test tubes.

8. Clean up your materials, and wash yourhands before leaving the lab.

9. In your lab report, make a histogram showing the totalnumber of shrimp you counted in each section of tubing.

Experimental Group

1. Set a fluorescent lamp 20 cm away from the tubing.2. Cover section 1 of the tubing with eight layers of

screen. Place four layers of screen on section 2 andtwo layers of screen on section 3. Leave section 4uncovered. Leave this setup in place for 30 minutes.While you are waiting, create a data table in your labreport like Table B, below, to record the numbers ofshrimp in each section of the tubing.

3. After 30 minutes have passed, attach screw clamps toeach spot that you marked on the tubing. While yourpartner holds the corks firmly in place, tighten themiddle clamp first, and then tighten the outer clamps.

4. Immediately pour the contents of each section of tub-ing into the test tube labeled with the correspondingnumber.

5. CAUTION If you get methyl cellulose in youreyes, immediately flush it out at the eyewash

station while calling to your teacher. Stopper testtube 1, and invert it gently to distribute the shrimp.Use a pipet to draw a 1 mL sample of shrimp cultureand transfer the culture to a Petri dish. Add a fewdrops of methyl cellulose to the Petri dish to slowdown the shrimp. Count the live shrimp, and recordthe count in your lab report.

6. Dispose of the shrimp as your teacher directs.Repeat step 5 four more times for a total of five

counts from test tube 1.7. Calculate the average number of shrimp in test tube 1,

and record the result in the data table you made inyour lab report.

8. Repeat steps 5–7 for the contents of each of theremaining test tubes.

9. Clean up your materials, and wash yourhands before leaving the lab.

10. In your lab report, make a histogram showing thenumber of shrimp in each section of tubing. Identifyeach section with the amount of screen.

Analysis and Conclusions

1. Describe the differences between the histogram of thecontrol group and the histogram of the experimentalgroup.

2. Why was a control (Part B) necessary?3. How did the brine shrimp react to differences in light?

Justify your conclusion.

Further Inquiry

Design an experiment to test the reaction of brine shrimpto a gradient of heat.

PART C

TABLE B EXPERIMENTAL GROUP

AverageTest number oftube Count Count Count Count Count shrimp innumber 1 2 3 4 5 test tube

1

2

3

4

379

Answers to Background3. Organisms select habitats in which conditions such

as temperature, light levels, salinity, and pH arewithin their tolerance limits. Brine shrimp, forexample, select for temperature, light, and pH.

4. A niche is all of an organism’s interactions with its living and nonliving environment, including itshabitat preferences.

TEACHER RESOURCES

Workbooks

Datasheets for In-Text Labs• Observing Habitat Selection

Skills Practice Labs• Assessing Abiotic Factors in the

Environment

Biotechnology Labs• Oil-Degrading Microbes

Technology

Biology Lab Video with Manual• Observing How Brine Shrimp Select a Habitat

GENERAL

5 unit ecology · each of the variety of organisms on earth depends in some way on other living and...

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