chapter 4: population biology - wikispacesjohnbio.wikispaces.com/file/view/chap04.pdf · bdol...

Products Available FromGlencoeTo order the following products,call Glencoe at 1-800-334-7344:VideodiscGTV: Planetary Manager

Index to NationalGeographic MagazineThe following articles may beused for research relating to thischapter.“Feeding the Planet,” by T. R.Reid, October 1998.“Human Migration,” by Michael

Parfit, October 1998.“Population,” by Joel L.Swerdlow, October 1998.“Making Sense of theMillennium,” by Joel L.Swerdlow, January 1998.“The World’s Food Supply atRisk,” by Robert E. Rhoades,April 1991.“Beyond Supermouse: ChangingLife’s Genetic Blueprint,” byRobert F. Weaver, December1984.“World’s Urban Explosion,” byRobert W. Fox, August 1984.

Teacher’s Corner

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Population BiologyPopulation Biology

TransparenciesReproducible MastersSection

PopulationDynamics

HumanPopulationGrowth

Section 4.1

Section 4.2

Teacher Classroom Resources

Reinforcement and Study Guide, pp. 15-16Concept Mapping, p. 4Critical Thinking/Problem Solving, p. 4BioLab and MiniLab Worksheets, p. 17Laboratory Manual, pp. 23-30Content Mastery, pp. 17-18, 20

Reinforcement and Study Guide, pp. 17-18BioLab and MiniLab Worksheets, pp. 18-20Content Mastery, pp. 17, 19-20 L1

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Section Focus Transparency 8Reteaching Skills Transparency 6

Section Focus Transparency 9

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Assessment Resources Additional ResourcesSpanish ResourcesEnglish/Spanish AudiocassettesCooperative Learning in the Science ClassroomLesson Plans/Block SchedulingReviewing Biology: Preparing to Take the EOC Test, pp. 7-8North Carolina Teacher Resource Manual

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Chapter Assessment, pp. 19-24MindJogger VideoquizzesPerformance Assessment in the Biology ClassroomAlternate Assessment in the Science ClassroomExamView® Pro SofrwareBDOL Interactive CD-ROM, Chapter 4 quiz5 Days to the EOC Test

Chapter 4 OrganizerChapter 4 Organizer

Activities/FeaturesObjectivesSection

Population DynamicsNational Science EducationStandards UCP.1-3; A.1,A.2; C.4, C.5; F.2, F.4, F.5,F.6; G.1, G.2 (3 sessions, 1block)

Human PopulationGrowthNational Science EducationStandards UCP.1-3; A.1,A.2; C.4, C.5, C.6; F.4, F.5;G.1, G.3 (2 sessions, 1 block)

1. Compare and contrast exponentialand linear population growth.

2. Relate the reproductive patterns of different populations of organisms tomodels of population growth.

3. Predict effects of environmental factorson population growth.

4. Relate population characteristics to population growth rates.

5. Compare the age structure of rapidlygrowing, slow-growing, and no-growthcountries.

6. Hypothesize about problems that can becaused by immigration and emigration.

MiniLab 4-1: Fruit Fly Population Growth, p. 96Inside Story: Population Growth, p. 98Problem-Solving Lab 4-1, p. 99Investigate BioLab: How can you determinethe size of an animal population? p. 108Chemistry Connection: Polystyrene: Friendor Foe? p. 110

MiniLab 4-2: Doubling Time, p. 105Problem-Solving Lab 4-2, p. 106

Section 4.1

Section 4.2

MATERIALS LIST

BioLabp. 108 paper bag, beans (175), magicmarker, paper, pencil, calculator(optional)

MiniLabsp. 96 banana, glass jar, rubber band,fine cloth or wire mesh, paper, pencilp. 105 paper, pencil, calculator(optional)

Alternative Labp. 100 petri dish (2), radish seeds,paper napkins, wax paper, pipette,water, paper, pencil

Quick Demosp. 101 overhead projector, cardboard,checkersp. 106 none

Need Materials? Contact Carolina Biological Supply Company at 1-800-334-5551or at http://www.carolina.com

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Refer to pages 4T-5T of the Teacher Guide for an explanation of the National Science Education Standards correlations.

The following multimedia resources are available from Glencoe.

Biology: The Dynamics of LifeCD-ROM

BioQuest: Antarctic Food WebAnimation: Carrying Capacity

Videodisc ProgramCarrying Capacity

The Infinite VoyageThe Keepers of Eden

The Secret of Life SeriesCompetitionPredator–PreyGone Before You Know It: The Biodiversity Crisis

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Key to Teaching StrategiesKey to Teaching Strategies

Level 1 activities should be appropriatefor students with learning difficulties.Level 2 activities should be within theability range of all students.Level 3 activities are designed for above-average students.ELL activities should be within the abilityrange of English Language Learners.

Cooperative Learning activitiesare designed for small group work.These strategies represent student prod-ucts that can be placed into a best-workportfolio.These strategies are useful in a blockscheduling format.

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http://www.carolina.com

Section

Principles of Population Growth

How and why do populationsgrow? Population growth is definedas an increase in the size of a popula-tion over time. Scientists use a vari-ety of methods to investigate popula-tion growth in organisms, as shownin Figure 4.1. One method involvesplacing microorganisms, such as bac-teria or yeast cells, into a tube or bot-tle of nutrient solution and observinghow rapidly the population grows.Another method involves introducing

4.1 POPULATION DYNAMICS 95

Weeds! You’ve probably observeda scene like this before. Whatwas recently a clean, grass-

filled lawn is now crowded with hun-dreds, perhaps thousands, of bright yel-low dandelions. Why do these plantsappear so quickly and in such largenumbers? Each season a dandelionplant produces hundreds of seeds. Incontrast, the lion produces onlytwo to four cubs when it suc-cessfully mates. Despite thedifferent reproductivemodes, dandelion popula-tions and lion popula-tions have lived in theirhabitats for thousands ofyears.

SECTION PREVIEW

ObjectivesCompare and contrastexponential and linearpopulation growth.Relate the reproduc-tive patterns of differ-ent populations oforganisms to models of population growth.Predict effects of environmental factorson population growth.

Vocabularyexponential growthcarrying capacitydensity-dependent

factordensity-independent

factor

4.1 Population Dynamics

Figure 4.1 Ecologists canstudy populationgrowth by inocu-lating a petri dishcontaining a nutri-ent medium witha few organismsand watchingtheir growth.

Dandelions(above) and alioness withcub (inset)

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Section 4.1

BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Use with Chapter 4,Section 4.1

How is the number of sea urchins in this communityaffected by the number of sea otters?

How is the number of sea otters affected by the number of sea urchins?

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SECTION FOCUS

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Transparency Predator-PreyRelationships8

PrepareKey ConceptsPopulation growth is the increasein population size over time.Students learn that populationgrowth, while exponential attimes, is controlled by limitingfactors that determine the carry-ing capacity of the environment.Such limits to population growthmay result from predator-preyinteractions or overcrowding.

Planning■ Purchase bananas and gather

jars and mesh for MiniLab 4-1.

■ Purchase radish seeds. Gatherpetri dishes and napkins forthe Alternative Lab.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 8 on the overhead pro-jector and have the studentsanswer the accompanying ques-tions.

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LSAssessment PlannerAssessment PlannerPortfolio Assessment

Portfolio, TWE, pp. 98, 104Problem-Solving Lab, TWE, p. 99Assessment, TWE, p. 103MiniLab, TWE, p. 105

Performance AssessmentMiniLab, SE, pp. 96, 105Assessment, TWE, pp. 100, 107Alternative Lab, TWE, pp. 100-101BioLab, SE, p. 109

Knowledge AssessmentSection Assessment, SE, pp. 103, 107Problem-Solving Lab, TWE, p. 106Chapter Assessment, SE, pp. 111-113

Skill AssessmentMiniLab, TWE, p. 96Assessment, TWE, pp. 102,105BioLab, TWE, p. 109

94 POPULATION BIOLOGY

Population Biology

What You’ll Learn■ You will explain how popula-

tions grow. ■ You will identify factors that

inhibit the growth of popula-tions.

■ You will summarize forcesbehind and issues in humanpopulation growth.

Why It’s ImportantHow a population grows is criti-cal to its niche. A populationthat becomes too large tooquickly may run out of foodand space, and diseases spreadmore easily through large pop-ulations; a population thatgrows too slowly may becomeextinct.

Carefully read the “InsideStory: Population Growth”on page 98. Observe thefive numbered stages ofpopulation growth. Choosea specific animal and itshabitat. Describe how eachstage of population growthwould unfold for the animaland impact the surroundingenvironment.

To find out more about popu-lation biology, visit theGlencoe Science Web site.science.glencoe.com

READING BIOLOGYREADING BIOLOGY

4ChapterChapter

The walruses (Odobenus rosmarus) in this large groupmake up one population.

BIOLOGY

Theme DevelopmentThe theme of systems and inter-actions is illustrated as changes inpopulations (the system) resultfrom interactions occurring with-in the population.

MultipleLearningStyles

Look for the following logos for strategies that emphasize different learning modalities.

Kinesthetic Project, p. 96

Visual-Spatial Project, p. 98; Portfolio, p. 98; Meeting

Individual Needs, p. 102

Linguistic Biology Journal, pp. 97, 99; Portfolio, p. 104;

Activity, p. 107Logical-Mathematical Enrich-ment, p. 97; Activity, p. 103;

Tech Prep, p. 104

GETTING STARTED DEMOGETTING STARTED DEMO

Have the class calculatethe growth of a popula-tion of 10 bacteria that

doubles every two hours. Visual-ize the growth by using pokerchips for the first five two-hourperiods. Every two hours, thenumbers double: 10, 20, 40, 80,160, 320, 640, 1280, 2560, 5120,10 240, to 20 480. Ask studentswhy bacteria don’t take overthe world. They run out offood, space, or other needs.Discuss the walruses shown inthe photograph, and ask whytheir population doesn’t growas quickly. They have fewer off-spring less often. Establish thatcrowding makes life more stress-ful and can spread disease.

Resource ManagerResource Manager

Section Focus Transparency8 and Master

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Glencoe’s Biology: The Dynamicsof Life contains many resourcesto assist a student’s reading skills.Each chapter contains figureswith expanded captions thatexpand on written material. WordOrigins, located along the side oftext, expand knowledge of biologyvocabulary. Glencoe’s ContentMastery Booklet helps developreading skills while reinforcingcontent. In addition, use theInteractive Tutor for Biology: TheDynamics of Life on the GlencoeWeb site to reinforce vocabulary.science.glencoe.com

Chapter 4Chapter 4

READING BIOLOGYREADING BIOLOGY

http://science.glencoe.com


Fruit Fly Population Growth Fruit flies (Drosophila melanogaster) and similar insects have rapid rates of reproduc-tion. Fruit flies are fre-quently used in biological research because they reproduce quickly and are easy to keep and count. In this activity you will observe the growth of a fruit fly population as it exploits a food supply.

Procedure! Place half of a banana in a jar and allow it to sit outside in

a warm shaded area, or put it in a warm area in yourclassroom.

@ Leave the jar for one day or until you have at least threefruit flies in it. Put the mesh on top of the jar and fastenwith the rubber band.

# Each day record how many adult fruit flies are alive in thejar. Record for at least three weeks. Put your data intotable form. CAUTION: Return the fruit flies to yourteacher for proper disposal.

Analysis1. How many fruit flies did you start with? On what day

were there the most fruit flies? How many were there?2. Why did the number of fruit flies decrease?3. Based on this investigation, why are insects considered to

display a rapid reproduction pattern?

MiniLab 4-1MiniLab 4-1 Making and Using Tables

a plant or animal species into a newenvironment that contains abundantresources and then observing thepopulation growth of that species.

Use the MiniLab on this page todemonstrate this method of measur-ing population growth. Throughstudies such as these, scientists haveidentified clear patterns showing howand why populations grow.

How fast do populations grow?What’s interesting about the

growth of populations is that it isunlike the growth of some otherfamiliar things. Consider, for example,the growth of a weekly paycheck foran after-school job. Suppose you areworking for a company that pays you$5 per hour. You know if you work fortwo hours, you will be paid $10; if youwork for four hours, you will be paid$20; if you work for eight hours, youwill be paid $40; and so on. When youplot this rate of increase on a graph, asshown in Figure 4.2, you can see thatthe result is a steady, linear increase;that is, growth occurs in a straight linewhen graphed.

Populations of organisms do notexperience this linear growth. Rather,the resulting graph of a growing pop-ulation first resembles a J-shapedcurve. Whether the population is one


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Money Earned Per Hour

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$100

$50

5 10 15 20 25 30 35 40

$80

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Figure 4.2 The way you earn money atan hourly rate is a straightline graph. Other examplesmight include the growth ofyour weekly allowance or thenumber of cars produced byan assembly line each month.

2 Teach

Purpose Students will learn that food is afactor in population growth.

Process Skillsobserve and infer, interpret data

Safety PrecautionsHave students wash their handsafter each observation.

Teaching Strategies■ If temperatures are warmenough, fruit flies should beattracted quickly to the bananas.■ You can order wingless fruitflies from a biological supplycompany.■ Have students record theirdata and observations in a table.

Expected resultsFruit flies will arrive and quicklyreproduce. Larvae will be evidenton the jar and the banana. In a fewweeks, the jar will be full of flies.Soon the population will declinebecause the food supply is limited.

Analysis1. Answers will vary.2. lack of food due to over-

crowding3. The population quickly in-

creased and then quicklydecreased.

Skill Have students des-cribe how they could determinewhether food type affects the typeof animal attracted. Use thePerformance Task AssessmentList for Designing an Experimentin PASC, p. 23. L2

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AssessmentAssessment

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MiniLab 4-1MiniLab 4-1

MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

Learning DisabledReview the proper construction of a graphwith students and/or refer them to theSkill Handbook. Assign students to coop-erative groups of mixed ability levels.Have them prepare graphs from data thatyou supply to illustrate linear and expo-nential changes.

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P R O J E C TFruit Fly Demographics

Kinesthetic Fruit flies are easy tomaintain in captivity. Allow students

to carry out an experiment that will com-pare a population of fruit flies kept inbalance with their environment with onenot kept in balance. Students will firsthave to determine how this balance willbe maintained.

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CD-ROMBiology: The Dynamicsof Life

BioQuest: Antarctic Food Web,Disc 1

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of weeds in a field, frogs in a pond, orhumans in a city, the initial increase inthe number of organisms is slowbecause the number of reproducingorganisms is small. Soon, however, therate of population growth increasesrapidly because the total number ofpotentially reproducing organismsincreases. This pattern illustrates theexponential nature of populationgrowth. Exponential growth meansthat as a population gets larger, it alsogrows faster. Exponential growth, asillustrated in Figure 4.3, results in apopulation explosion.

Limits of the environmentCan a population of organisms

grow indefinitely? What prevents theworld from being overrun with allkinds of living things? Through pop-ulation experiments, scientists havefound that, fortunately, populationgrowth does have limits. Eventually,limiting factors, such as availability offood and space, will cause a popula-tion to stop increasing. In time, thisleveling-off of population size resultsin an S-shaped growth curve.

The number of organisms of onespecies that an environment can sup-port is its carrying capacity. Whenpopulations are under the carryingcapacity of a particular environment,births exceed deaths until the carryingcapacity is reached. If the populationtemporarily overshoots the carryingcapacity, deaths exceed births untilpopulation levels are once againbelow carrying capacity. Thus, thenumber of organisms in a populationis sometimes more than the carryingcapacity and sometimes less. Learnhow to determine population size bycompleting the BioLab at the end ofthis chapter. When the populationfalls below the carrying capacity, thepopulation tends to increase; when itis above the carrying capacity, the

population tends to decrease. Do allpopulations follow the same growthpattern? Find out in the Inside Storyon the next page.

Patterns of population growthIn nature, many animal and plant

populations change in size. Why, forexample, does it seem like mosquitoesare more numerous at certain times ofthe year? Why don’t populationsreach carrying capacity and becomestable? To answer these questions,population biologists study the mostimportant factor that determines pop-ulation growth—an organism’s repro-ductive pattern.

A range of population growth pat-terns are possible in nature. The twoextremes of this range are demon-strated by the population growth ratesof both mosquitoes and elephants.Mosquitoes reproduce very rapidlyand produce many offspring in a shortperiod of time. Elephants have a slowrate of reproduction and produce rela-tively few young over their lifetimes.What causes species to have differentlife-history patterns?


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Figure 4.3 Because they growexponentially, popula-tions such as house-flies have the poten-tial for explosivegrowth.

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ReinforcementExplain that while linear growthmay be shown by height increasesin children, it does not reflect thegrowth pattern of most popula-tions.

Chalkboard ExampleGraph two lines onto the sameaxis using different colors ofchalk. Have one line show lineargrowth, and the other line showexponential growth. Ask studentsto describe how the patterns dif-fer. Point out that when thecurves begin, differences aresmaller than at the end points.

EnrichmentLogical-MathematicalHave students make

the calculations needed to decideif they would rather be paid a lin-ear salary of $5.00 per hour for a40-hour week or an exponentialsalary that starts at 1 cent the firsthour and doubles each hour up to40 hours. The exponential salarywill exceed the linear salary manytimes over. L2

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BIOLOGY JOURNAL BIOLOGY JOURNAL

Evaluating Population GrowthLinguistic Have students write ascenario that depicts what life in

the United States might be like if thepopulation doubled. Have them consideravailable recreational space, demandsmade on natural resources, and food andhousing needs.

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The BioLab at theend of the chaptercan be used at thispoint in the lesson.

INVESTIGATEINVESTIGATE

CD-ROMBiology: The Dynamicsof Life

Animation: Carrying CapacityDisc 1

VIDEODISCBiology: The Dynamicsof Life

Carrying Capacity (Ch. 13)Disc 1, Side 117 sec.!8JÇ"Resource ManagerResource Manager

BioLab and MiniLab Worksheets,p. 17

Laboratory Manual, pp. 23-30 L2

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Population Growth

When organisms are in an optimal environment, theyflourish. From a few pioneers, the population increases.

Ecologists have discovered that these population increasesshow a pattern. Whether it is a plant or animal, whether onland or in the ocean, populations grow in predictable manners.

Critical Thinking Why does the population fluctuate once itreaches carrying capacity?

Humpback whales have a long life-history, living up to thirty years.

INSIDESSTORTORYY

INSIDE

Beginning growth The popu-lation increases, the few start-ing members have offspring,and the population grows.

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Rapid growthThere are manyorganisms, eachreproducing, result-ing in a fast increasein the number ofindividuals. Growthis exponential.

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Leveling off As the popu-lation grows, it becomesmore difficult for eachorganism to meet its needs.Growth slows. The graphresembles the letter S.

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Carrying capacity Theenvironment cannot supportmore organisms. If populationsize is above the carryingcapacity, organisms die.

44 Fluctuations Thenumber of organismstends to rise aboveand below the carryingcapacity.

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IINSIDENSIDESSTORTORYY

INSIDE

Purpose Students study the general pat-tern of population growth in sta-ble environments.

Teaching Strategies■ Have students write a one-paragraph summary of how apopulation grows, including whythe population levels off.■ Have students become one ofthe original animals in a popula-tion that grows quickly. Ask themto write a fictional account ofwhat happens from the animal’sperspective.■ The Project Wild simulation“Oh, Deer!” is an excellentmethod of simulating that fluctu-ations above and below the carry-ing capacity are normal.■ Give each group of students adie. For time period 1, they rollthe die and record the numberthat shows up as a populationsize. Do the same for time period2, 3, all the way to 10. On the x-axis, plot the time periods 1 to10. On the y-axis, plot the popu-lation size. Have them find theaverage population size for the 10time periods and draw a straightline to reflect this average. Relatethis line to carrying capacity.

Critical ThinkingThe population begins exponen-tial growth. This resembles theletter J. Eventually growth slowsdown and the population levelsoff. After it levels off, it fluctuatesabove and below the carryingcapacity.

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PortfolioPortfolio

Interpreting GraphsVisual-Spatial Ask students to drawan S-shaped curve. Have them iden-

tify the following: slow growth phase,exponential growth phase, plateau, pointwhere carrying capacity (K) is reached. Askhow this graph might change with a sud-den increase or decrease in food supply.

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P R O J E C TPopulation Growth in Pictures

Visual-Spatial Have students createflipbooks that show population

growth. Draw scenes on the right sides ofindex cards. On the first cards, show a feworganisms, then exponential growth. Showcompetition for resources. Then show a constant population size. A line on a graphcan advance in each scene.

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How rapidly can bacteria reproduce? The faster anorganism reproduces, the quicker you can see populationincreases. Bacteria are examples of rapidly reproducingorganisms. Thus, they are often used in experiments that deal with population studies or trends.

AnalysisHere are some facts regarding unchecked bacterial repro-

duction:1. A single bacterium can reproduce to yield two bacteria

under ideal conditions every 20 minutes.2. Ideal conditions for bacterial reproduction include proper

temperature, unlimited food, space to grow, and disper-sion of waste materials.

Thinking Critically 1. Suppose you start with one bacterium under ideal condi-

tions. If no bacteria die, compute the number of bacteriapresent after 1 hour, 5 hours, and 10 hours.

2. What environmental factors might affect a bacterial pop-ulation’s reproduction?

3. The above graph is an example of one group’s data:a. What error did they make in the y-axis of the graph? b. Redraw the graph correctly.

4. An elephant reproduces once every four to six years. Whyare elephants not likely to be used in laboratory popula-tion studies?

Problem-Solving Lab 4-1Problem-Solving Lab 4-1 PredictingThe kind of reproductive pattern a

species has depends mainly on envi-ronmental conditions. For example,species such as mosquitoes are suc-cessful in environments that areunpredictable and change rapidly.Rapid life-history patterns are foundin organisms from unpredictableenvironments. Typically, these organ-isms have a small body size, maturerapidly, reproduce early, and have ashort life span. Populations of theseorganisms increase rapidly, thendecline rapidly as environmental con-ditions suddenly change and becomeunsuitable. The small surviving pop-ulation will begin reproducing expo-nentially when conditions are againfavorable. The Problem-Solving Labon this page will allow you to observean organism with this type of a life-history pattern, bacteria.

Species that live in more stableenvironments, such as elephants,often have a different life-history pat-tern. Elephants, humans, bears,whales, and long-lived plants, such ascacti and bristlecone pine shown inFigure 4.4, are large, reproduce andmature slowly, and are long-lived.These organisms maintain popula-tion sizes near the carrying capacitiesof their environments.

Although populations could displaya variety of life-histories, under


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Figure 4.4This bristlecone pine isan example of a long-lived species with a slowlife-history pattern.

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Purpose Students will calculate the changein number of individuals presentin a bacterial population.

Process Skillscalculate, think critically, predict,apply concepts, make and usegraphs, organize data

Teaching Strategies■ Allow students to use calcula-tors.■ Suggest that they prepare theirown data table to record thenumber of bacteria present dur-ing each time period.Example:

Time Number(in minutes) Present

0 120 240 4

60 (1 hour) 880 16

Thinking Critically1. 8; 32 728; 1 072 431 1042. Answers may include temper-

ature, light, and pollution.3. a. The y-axis is not properly

scaled.b. Check students’ graphs foraccuracy.

4. Answers may include thelong time period betweengenerations and the size ofthe animals.

Portfolio Ask students towrite a paragraph for their portfo-lios, evaluating the use of yeast,mice, and primates in populationstudies. Use the Performance TaskAssessment List for Writing inScience in PASC, p. 87. PP

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Problem-Solving Lab 4-1Problem-Solving Lab 4-1

BIOLOGY JOURNAL BIOLOGY JOURNAL

Life as a MosquitoLinguistic Have students imaginethey are breeding mosquitoes. Tell

them to describe the conditions thatmake their environment unpredictableand subject to rapid change. Studentswill have to research life stages andbreeding habits of mosquitoes to com-plete this task.

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VIDEODISCThe Infinite Voyage: The Keepers ofEden, Extinction and the National

Zoo’s Tamarin Monkey Project(Ch. 4) 13 min. 30 sec.!7KVF"

The Cheetah: Using DNA Profiles to ResearchReproduction (Ch. 5) 9 min.!7U`H"


Reteaching Skills Trans-parency 6 and Master

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uncrowded conditions, such as thepioneer stage in succession, rapid pop-ulation growth seems to be most com-mon. Figure 4.5 shows organisms thatrepresent both extremes in life-historypatterns. Which of these organismswould be most successful in a rapidlychanging environment?

Environmental limits to population growth

Limiting factors, you may remem-ber, include biotic or abiotic factorsthat determine whether or not anorganism can live in a particular envi-ronment. Limiting factors also regu-late the size of a population. Limitedfood supply, extreme temperatures,and even storms can affect popula-tion size. Ecologists have identifiedtwo kinds of limiting factors: density-dependent and density-independentfactors.

Density-dependent factorsinclude disease, competition, para-sites, and food. These have anincreasing effect as the populationincreases. Disease, for example,spreads more quickly in a populationwith members that live closetogether, as indicated in Figure 4.6,than in smaller populations withmembers that live farther apart. Invery dense populations, disease mayquickly wipe out an entire population.In crops such as corn or soybeans inwhich large numbers of the sameplant are grown together, a diseasecan spread rapidly throughout the


Figure 4.6 Corn smut is a fungusthat produces large,deformed growthson the ears of corn.To prevent it fromspreading through acornfield, affectedplants must beburned or buriedbefore the fungusreproduces.

Figure 4.5 Wild mustard plants taking over an aban-doned field represent a species with arapid life-history pattern (a). Organismsthat have a slow life-history pattern, suchas these Canada geese, provide muchparental care for their young in order toensure species survival (b).

a

b

Alternative LabGerminating Radishes

Purpose Students will study the percent of germination of radish seeds.Safety PrecautionsHave students wash their hands afterhandling the seeds.

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Materials per grouptwo petri dishes, radish seeds, napkins, pipetteProcedureModel the method of germination: Cut a nap-kin into two circles that will fit into a petridish. Place one circle into the dish, put someseeds on top, and place the other circle on topof the seeds. Add a pipette or two of water.Cover the dish. Then give students theseinstructions

1. With your group, choose one variable to

change, such as the amount or type ofsolution used for watering. You couldalso investigate the effects of heat,light, or music.

2. Complete this problem statement:What is the effect of __________ on thegermination of a radish seed? Write ahypothesis to answer this question.

3. Write out your procedures before start-ing. Plan for a control and an experi-mental group. 100

VIDEODISCGTV: PlanetaryManager

Agriculture, Side 2

!7S-~I"

Revealing MisconceptionsExponential growth may be mis-understood. Some students maythink that (1) the growth ratemust be very fast and (2) thegrowth rate increases. Use thisanalogy to help. You put $100 inthe bank and get 10% interest ayear. How much will you haveafter the first five years? $110,$121, $133, $146, $161

The big idea is that althoughthe account grows only at a slowand constant 10% a year, growthbuilds upon growth. This is whatexponential growth is all about.

Revealing MisconceptionsHelp students realize that mostorganisms fall in a continuumbetween rapid life-histories andslow life-histories. These are theextremes of the scale.

Performance Assessmentin the Biology Classroom, p. 53,Estimating Populations. Have stu-dents carry out the activity to showtheir knowledge of how popula-tion size is determined. L2

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whole crop. In less dense populations,fewer individuals may be affected.

Density-independent factorsaffect all populations, regardless oftheir density. Most density-indepen-dent factors are abiotic factors, suchas temperature, storms, floods,drought, and habitat disruption,shown in Figure 4.7. No matter howmany earthworms live in a field, theywill drown in a flood. It doesn’t mat-ter if there are many or few mosqui-toes; a cold winter will kill them.Another example of a density-inde-pendent factor is pollution. Howdoes pollution affect a habitat? Findout in the Chemistry Connection at theend of this chapter.

Organism InteractionsLimit Population Size

Population sizes are limited not onlyby abiotic factors, but also are con-trolled by various interactions amongorganisms that share a community.

Predation affects population sizeA barn owl kills and eats a mouse.

A swarm of locusts eats and destroysacres of lettuce on a farm. When thebrown tree snake was introduced inGuam, an island in the South Pacific,it wiped out most of the birds on theisland. These examples demonstratehow predation can affect populationsizes in both minor and major ways.When a predator consumes prey, itcan affect the population size of theprey population. For this reason, pre-dation may be a limiting factor ofpopulation size.

Populations of predators and preyexperience changes in their numbersover a period of years. Predator-preyrelationships often show a cycle ofpopulation increases and decreasesover time. One classic example of this has been demonstrated by graph-ing 90 years of data concerning thepopulations of the Canadian lynx andthe snowshoe hare. A member of thecat family, the lynx stalks, attacks,


Hurricane Mitch, which hitsouth Florida in 1998, didextensive damage to bothheavily populated areas and less populated ones.Catastrophic weather patterns are density-independent factors.

AA

Figure 4.7 Populations are affected by bothdensity-dependent and density-independent factors.

As a population of foxes increases,competition for theavailable food alsoincreases. Foodbecomes a density-dependent factorand populationgrowth slows.

BB

4. Set up your experiments and wait 48hours. Then report your results. Wasyour hypothesis correct?

Analysis1. Why do plants produce so many seeds?

Not all seeds germinate.2. Was your variable a biotic or abiotic

factor? Most will be abiotic factors.3. What was your conclusion for your

experiment? Answers will vary.

Performance Have students writea lab report describing the procedurethey followed and their conclusions. Usethe Performance Task Assessment Listfor Lab Report in PASC, p. 47. L1

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101

Quick DemoQuick Demo

Cut out a cardboard framethat is a little smaller than thesize of the glass of the overheadprojector. Put three checkersinto the frame. Move the frameand cause the checkers to moveabout. Stop. If any checkers arewithin one cm of another, theydie. Repeat, adding more check-ers. Students will realize that themore crowded it gets, the great-er the number of checkers thatdie. Have them relate this todensity-dependent factors.

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VIDEODISCThe Secret of LifeCompetition

Predator-Prey

!<C<XEBB"

!<<UX9LJ"

Visual LearningAsk students to study Figure 4.7B and explain what will hap-pen to prey populations of miceand rabbits as the predator foxpopulation increases. The rabbitand mice populations will decline.


Critical Thinking/ProblemSolving 4, p. 4

Concept Mapping, p. 4

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and eats the snowshoe hare as a pri-mary source of food.

The data in Figure 4.8 show thelynx and hare populations rise andfall almost together. When the harepopulation increases, there is morefood for the lynx population, and thelynx population increases. When thelynx population rises, predation onthe hares increases, and the hare pop-ulation decreases. With fewer haresavailable for food, the lynx popula-tion also declines. With fewer preda-tors, the hare population increases,and the cycle continues. This exam-ple shows how predator populationsaffect the size of the prey popula-tions. At the same time, prey popula-tions affect the size of the predatorpopulations. As the snowshoe hare’sfood supply of grasses and herbsdwindles during the fall and wintermonths, the hare populationdecreases. Because there are nowfewer hares to hunt, the lynx popula-tion also decreases. With the returnof spring, the hare’s food supply and

its population recover. This leads tomore hares, allowing the lynx popu-lation to increase as well.

Predator-prey relationships areimportant for the health of naturalpopulations. Usually, in prey popula-tions, the young, old, or injuredmembers are caught. Predation helpsimprove the odds that there will besufficient resources for the healthiestindividuals in a population.

The effects of competitionOrganisms within a population

constantly compete for resources.When population numbers are low,resources are plentiful. However, aspopulation size increases, competi-tion for resources such as food, water,and territory can become fierce.Competition is a density-dependentfactor. When only a few individualscompete for resources, no problemarises. When a population increasesto the point at which demand for


Num

ber o

f org

anism

s (in

thou

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s)

Time (in years)

Lynx and Hare Pelts Sold to the Hudson Bay Company

180

160

140

120

100

80

60

40

20

01845 1855 1865 1875 1885 1895 1905 1915 1925 1935

Lynx

Hare

Figure 4.8The data in thisgraph reflect thenumber of hare andlynx pelts sold to theHudson Bay Companyin northern Canada.Notice that as thenumber of haresincreased, so did thenumber of lynx.

102

Tying to PreviousKnowledgeExplain how the decrease in avail-able energy at the top trophiclevel of a food chain serves as alimiting factor on predator popu-lation size.

Visual LearningAsk students to study the graph inFigure 4.8 and identify the pointat which the numbers of snow-shoe hare and lynx began toincrease. Have them also indicatewhere decreasing numbers occur.Use the graph to point out thecyclic nature of these events.Elicit from students why theseevents are cyclic.

Skill Have students exam-ine Figure 4.8 and answer thesequestions: In what approximateyear were there the most hares?1865 In what year were there themost lynxes? 1935 After the harepopulation spikes, how manyyears pass until it crashes? approx-imately 5 years

3 AssessCheck for UnderstandingAsk students to explain the differ-ence between the words in eachof the following pairs.

a. linear growth—exponentialgrowth

b. carrying capacity—popula-tion size

c. density-dependent factors—density-independent factors

d. predation—competition

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MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

Learning DisabledVisual-Spatial Have students tapethe outlines of two squares, measur-

ing 10 cm per side. Ask them to use pen-nies to illustrate a dense population in onesquare and a less dense population in theother square. Ask them to predict whichpopulation is more vulnerable to disease.the dense population

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VIDEODISCGTV: PlanetaryManager

Animal, Side 2

!7RTVF"

VIDEOTAPEThe Secret of Life

Gone Before You Know It: The BiodiversityCrisis

resources exceeds the supply, thepopulation size decreases.

The effects of crowding and stress

When populations of organismsbecome crowded, individuals mayexhibit stress. The factors that createstress are not well understood, butthe effects have been documentedexperimentally in populations of ratsand mice, as shown in Figure 4.9. As


Section AssessmentSection AssessmentUnderstanding Main Ideas1. How are graphs of exponential growth and lin-

ear growth different?2. Explain how short and long life-history patterns

differ.3. Describe how density-dependent and density-

independent factors regulate populationgrowth.

4. How can a density-independent factor, such as aflood, influence carrying capacity?

Thinking Critically5. An organic farmer does not use pesticides on her

farm. Instead of growing one crop on her farm,as many farmers do, she grows ten differentcrops. Explain how this may decrease insect dam-age to her plants.

6. Making and Using Graphs Graph the follow-ing population growth for the unknown organ-ism shown in Table 4.1 and state whether theorganism has a population growth pattern closerto a rapid or slow life-history pattern. For morehelp, refer to Organizing Information in the SkillHandbook.

SKILL REVIEWSKILL REVIEW

Figure 4.9 Stress caused by overcrowding in a ratpopulation can limit population size.When overcrowded, animals fight andkill each other, they reproduce less,and they stop caring for offspring.

Year

1995

1996

1997

Spring

564

750

365

Summer

14 598

16 422

14 106

Autumn

25 762

42 511

36 562

Winter

127

102

136

Table 4.1 Population of unknown organisms

populations increase in size, individ-ual animals begin to exhibit a varietyof symptoms, including aggression,decrease in parental care, decreasedfertility, and decreased resistance todisease. All of these symptoms canlead to a decrease in population size.

ReteachHave students provide an exam-ple that shows an understandingof the meaning of each vocabu-lary word in this section.

ExtensionHave students research the termsr-strategists and K-strategists. Havethem provide characteristics andexamples for both groups andcorrelate this information withwhat they have studied in thischapter.

Portfolio Have studentsoutline the concepts in this sec-tion.

4 CloseActivity

Logical-Mathematical Askstudents to count the poten-

tial offspring (the number ofseeds) in one green pepper.Caution: Have them wash theirhands after handling seeds. Askwhy the world is not coveredwith green pepper plants. L2

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Section AssessmentSection AssessmentSection Assessment1. Linear growth graphs form a straight

line, and exponential graphs form acurved line described as J-shaped.

2. Short life-history organisms show arapid increase and rapid decline causedby their unpredictable environments.Long life-history organisms show aslow population change within stableenvironments and usually maintain

sizes near the carrying capacity of theenvironment.

3. Density-dependent factors have an increasing effect as population size increases. Density-independent factorsaffect a population no matter what itssize.

4. The flood could damage a habitat, thuslowering its carrying capacity.

5. Each kind of insect usually damagesspecific crops. When a farmer growsten crops, an infestation of one kind ofinsect is unlikely to affect all of hercrops.

6. The graphs should show a rapid life-history pattern. The organism repro-duces rapidly and declines rapidly.

103


Content Mastery, p. 18Reinforcement and Study

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Doubling Time The time needed for any population to dou-ble its size is known as its “doubling time.” For example, if apopulation grows slowly, its doubling time will be long. If it isgrowing rapidly, its doubling time will be short.

Procedure! The following formula is used to calculate a population’s

doubling time:

@ Copy the data table below. # Complete the table by calculating the doubling time of

human populations for the listed geographic regions.

Analysis 1. Which region has the fastest doubling time? Slowest dou-

bling time?2. How might this type of information be useful to govern-

ments of these regions?3. What are some of the ecological implications for an area

with a fast doubling time?

MiniLab 4-2MiniLab 4-2 Using NumbersEffects of birthrates and death rates

How can you tell if a population isgrowing? A population’s growth rateis the difference between the birthrateand the death rate. One way of calcu-lating a population’s growth rate is bycalculating its doubling rate. Learnhow to calculate doubling rates in theMiniLab on this page. In many indus-trialized countries, such as the UnitedStates, declining death rates have agreater effect on total populationgrowth than increasing birthrates.For example, in the United States, lifeexpectancy increases almost everyyear. This means that you are morelikely to live slightly longer than stu-dents who are presently in college.

Although people in the UnitedStates are living longer, the fertilityrate is decreasing. This is becausemore people are waiting until theirthirties to have children. Today’s fam-ilies also have fewer children thanthey did in previous decades. Fertilityrate is the number of offspring afemale produces during her reproduc-tive years. When fertility rates arehigh, populations grow more rapidlyunless the death rate is also high.Table 4.2 shows the birthrate, deathrate, and fertility rate of some rapidly

Geographicregion

Doublingtime

Annual percentgrowth rate

Africa

Latin America

Asia

North America

Europe

2.8

2.2

1.9

0.7

0.3

Data Table

Birthrate(per 1000)

38.8

50.8

34.3

9.4

9.4

10.8

27.0

14.8

Death Rate(per 1000)

5.5

21.8

9.4

10.8

9.7

10.6

5.2

8.8

Fertility(per woman)

3.3

7.1

5.2

1.2

1.2

1.5

3.1

2.0

Population increase(percent)

3.3

2.9

2.5

–1.5

–0.5

0.1

2.2

0.6

Table 4.2 Birthrates and death rates around the world

Rapid Growth Countries

Jordan

Uganda

Zimbabwe

Slow Growth Countries

Germany

Italy

Sweden

North American Countries

Mexico

United States 105

=Doubling time (in years) 70annual percent growth rate

2 Teach

Purpose Students will learn the concept of“doubling time” and use a formu-la to calculate this value.

Process Skillsuse numbers, acquire informa-tion, analyze information, com-pare and contrast, predict, recog-nize cause and effect

Teaching Strategies■ Organize the class into smallgroups. Place students withpoorer math skills with thosewho are more skilled.■ Allow students to use calcula-tors.■ The value of “70” used in theformula is a constant.

Expected ResultsAfrica = 25 years, Latin America =31.8 years, Asia = 36.8 years, N.America = 100 years, Europe =233 years

Analysis1. Africa; Europe 2. Answers may vary, but stu-

dents may mention the plan-ning of roads, homes, andother needed structures.

3. Students may list the highpotential for disease, problemwith waste disposal, and lackof space.

Portfolio Have studentsprepare a bar graph using theircalculated values for doublingtime. Use the PerformanceAssessment List for Graph fromData in PASC, p. 39.

Skill Ask students to useTable 4.2 to identify the factorsthat contribute to a high popula-tion growth rate. Responses mayinclude high birthrates, low deathrates, and high fertility rates. L2

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MiniLab 4-2MiniLab 4-2

Section


Demographic TrendsA good way to predict the future of

the human population is to look atpast population trends. For example,are there observable patterns in thegrowth of populations? That is, arethere any similarities among the pop-ulation growths of different coun-tries—similarities that might help

scientists predict, and therefore con-trol, future population catastrophes?As you have seen, some populationstend to increase until the environmentcannot support any additional growth.Demography (dem AH graf ee) is the study of human populationgrowth characteristics. Demographersstudy such population characteristicsas growth rate, age structure, and

geographic distribution. What is the history of pop-

ulation growth for humans?Although local human popula-tions often show fluctuations,the worldwide human popula-tion has increased exponen-tially over the past severalhundred years, as shown inFigure 4.10. Unlike otherorganisms, humans are able toreduce environmental effectsby eliminating competingorganisms, increasing foodproduction, and controllingdisease organisms.

Does Earth have a carrying capacityfor the human population? Howmany people can live on Earth? No

one knows how many people Earth can sup-port, and it is presently impossible to tellwhen the human population will stop grow-ing. However, demographers suggest thatfood production will not always keep pacewith the population increase.

SECTION PREVIEW

ObjectivesRelate populationcharacteristics to popu-lation growth rates.Compare the agestructure of rapidlygrowing, slow-growing,and no-growth coun-tries.Hypothesize aboutproblems that can becaused by immigrationand emigration.

Vocabularydemography age structureimmigration emigration

Billi

ons o

f peo

ple

Bubonic plagueTime

Change in the Human Population Over Time

1211109876543210 1 A

.D.

20001980

20302050

1850

1650

Earth from space

Figure 4.10Ten thousand yearsago, approximately10 million peopleinhabited Earth.Today, there are morethan 6 billion, andscientists estimatethat by the year2050, there will bemore than 10 billionpeople on Earth.

4.2 Human PopulationGrowth

104

Section 4.2

PrepareKey ConceptsPopulation growth is the increasein population size over time.Students learn that populationgrowth, while exponential attimes, is controlled by limitingfactors that determine the carry-ing capacity of the environment.Such limits to population growthmay result from predator-preyinteractions or overcrowding.

Planning■ Purchase beans, markers, and

bags for the BioLab.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 9 on the overhead pro-jector and have the studentsanswer the accompanying ques-tions.

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BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

6 hours 6 hours 6 hours 6 hours

Assuming the birthrate remains constant, how many parameciawould be produced in 30 hours?

What would be the population size of the paramecia in 24 hoursif one paramecium died during each six-hour period?

11

22

SECTION FOCUS

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Transparency Birthrates and Death Rates9



PortfolioPortfolio

Interpreting GraphsLinguistic Ask students to work withpartners to write a true and a false

statement that are both based on Table4.2. Have partners exchange statementsand identify which is true and which isfalse. L2

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Graphing Population GrowthLogical-Mathematical Have studentsmake a bar graph that shows the

population growth of each country inTable 4.2, from highest to lowest percent-age.

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Cultural DiversityFertile GroundsHave the class discuss reasons why develop-ing countries have high fertility rates.Cultural reasons could include (a) peopleprefer large families; (b) large families mayhave more prestige; and (c) religions mayban the use of birth control. There could besocioeconomic reasons as well. Statistics

suggest that there tend to be more babiesper woman in economically depressed coun-tries. Reasons might include (a) higher infantmortality may encourage people to havemore children; (b) families may have morechildren to help earn money; and (c) familiesdon’t have access to medical services or birthcontrol.

105

Population Distribution Per Age Range for Several Countries

80+

75-79

70-74

65-69

60-64

55-59

50-54

45-49

40-44

35-39

30-34

25-29

20-24

15-19

10-14

5-9

Under 5

Germany(stability)

Mexico(rapid growth)

United States(slow growth)

6 4 2 0 2 4 6 8 6 4 2 0 2 4 6 8

Population (percent)

6 4 2 0 2 4 6

Majorreproductive

ages

Age

MaleFemale

Movement from a population isemigration. Obviously, movement ofpeople between countries has noeffect on total world population, butit does affect national populationgrowth rates. Local populations can

also feel the effects of a moving pop-ulation. Many suburbs of large citiesare expanding rapidly. This placesstress on schools, roads, and policeand fire services. What other prob-lems result from suburban growth?

4.2 HUMAN POPULATION GROWTH 107

Figure 4.11 Notice that in a rapidlydeveloping countrysuch as Mexico, thelarge number of indi-viduals in their pre-reproductive years willadd significantly tothe population whenthey reach reproduc-tive age. Populationsthat are not growing,such as Germany’s,have an almost evendistribution of agesamong the popula-tion.

Section AssessmentSection AssessmentUnderstanding Main Ideas1. What characteristics of populations do demogra-

phers study?2. How does life expectancy affect death rate?3. What clues can an age structure graph provide

about a country’s population growth?4. Discuss some possible problems for local popula-

tions caused by immigration and emigration ofpeople.

Thinking Critically5. Using the age structure graph for the United

States in Figure 4.11, explain which gender

has a higher life expectancy and then suggest a hypothesis for why this difference exists.

6. Making and Using Graphs Construct a bargraph showing the age structure of Kenya using the following data: pre-reproductive years (0-14)—42 percent; reproductive years (15-44)—39 percent; post-reproductive years (45-85+)—19 percent. For more help, refer to Organizing Information in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

OriginWORDWORD

emigration From the Latinwords e, meaning“out,” and migrate,meaning “tomigrate.” Peopleemigrate when they move out of a country.

107

3 AssessCheck for UnderstandingHave students explain the rela-tionship between the words ineach of the following pairs.

a. population growth—birthand death rate

b. age of population—popula-tion growth

ReteachAsk students to explain how ahigh fertility rate with low deathrate will influence a population’ssize. Population will increase.

ExtensionHave students research the prosand cons of allowing large num-bers of immigrants to enter theUnited States.

Performance Have stu-dents write a paragraph thatexpresses their opinion as towhether the future size of humanpopulation should be controlled.

4 CloseActivity

Linguistic Have students listchanges that can increase

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Section AssessmentSection AssessmentSection Assessment1. Demographers study growth rate, age

structure, and geographic distribution.2. If life expectancies rise, death rates will

decrease.3. It can determine if a population is grow-

ing rapidly, slowly, or not at all.4. Answers will vary. Immigration can

increase the need for schools, medical

facilities, and public transportation.Emigration may result in unused facilitiesand vacant homes.

5. Female; hypotheses will vary, but mayinclude a healthier life style or differenthormone concentrations.

6. Evaluate students’ graphs for logic andaccuracy.

What trends are seen in the humanpopulation? Human populationtrends present some interestingideas and concepts. Because of ourintelligence, we are better able to control our population size,regulate our food supply, andremove waste products from our environment. Thus, human population trends may differ fromthose of other organisms.

AnalysisFigure 4.10 shows human population changes over time.

Study this graph and answer the questions below.

Thinking Critically1. What density-dependent factors can influence human

population growth? What density-independent factorscan influence human population growth?

2. Has the human population reached its carrying capacity?Explain why.

3. Based on the graph in Figure 4.10, what will be Earth’spopulation in the year 2010?

4. Determine the human population’s doubling time as itincreases from half a billion to one billion, from one totwo billion, and from two to four billion.

5. Explain the significance of the trend shown in question 4.6. Using the values for doubling time provided in question 4,

calculate the human population’s annual percent growthrate using the method described in the MiniLab on theprevious page. Use the formula below:

7. Explain the significance of the trend shown by youranswer to question 6.

Problem-Solving Lab 4-2Problem-Solving Lab 4-2 Applying Concepts

growing and slower growing coun-tries. Some countries, such as Uganda,have high death rates among childrenbecause of disease and malnutrition.However, these countries have highbirthrates, and their populations are growing rapidly. Some other countries, such as Sweden and Italy,have low death rates, but theirbirthrates are also low, so these coun-

tries’ populations are growing slowly,if at all.

As you can see, different combina-tions of birthrates and death rateshave different effects on populations.The birthrate, death rate, and fertil-ity rate of a country provide clues tothat country’s rate of populationgrowth. Learn more about humanpopulation trends in the Problem-Solving Lab on this page.

Does age affect populationgrowth?

Imagine a country filled mostlywith teenagers. Does it make a differ-ence to population growth if thelargest proportion of the populationis in one age group? In order to makepredictions about populations of thefuture, demographers must know theage structure of a population. Agestructure refers to the proportions ofa population that are at different agelevels. Age structure can be visual-ized by the use of graphs, as shown inFigure 4.11, and can help predict if apopulation is growing rapidly, grow-ing slowly, or not growing at all.Rapid growth countries have an agestructure with a wide base because alarge percentage of the population isteenagers and children. These youngpeople are likely to mature into adultsand have their own children. If thepercentage of people in each categoryis fairly equal, this indicates the popu-lation is stable, neither increasing nordecreasing.

Mobility has an effect on population size

Humans can move in and out ofdifferent communities. The effects ofhuman migrations can make it diffi-cult for a demographer to make pre-dictions, but patterns do exist.Movement of individuals into a pop-ulation is immigration.


A human population

=Doubling time (in years) 70annual percent growth rate

106

Purpose Students will analyze trends inhuman population changes.

Process Skillsthink critically, apply concepts,analyze information, use num-bers, draw a conclusion, make anduse graphs

Teaching Strategies■ Review the meanings of den-sity-dependent factors, density-independent factors, and carryingcapacity.■ Explain doubling time andannual percent growth if studentsdid not complete or discussMiniLab 4-2.■ Allow students to use calcula-tors.

Thinking Critically

1. Density-dependent: disease,war, immigration, emigra-tion, birth rate, death rate,availability of food or water.Density-independent: pollu-tants in water, soil, or air.

2. No. Humans are able to pro-vide food and water, removewastes, and prevent disease.

3. over 7 billion4. 200 years; 70 years; 55 years5. It is taking less and less time

for the human population todouble in size.

6. The values show an annualpercent growth rate rangingfrom 0.35% (1650–1850) to1.27% (1920–1975). Thetrend is one of higher growth

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Problem-Solving Lab 4-2Problem-Solving Lab 4-2

Quick DemoQuick Demo

If the information is available,help students construct an agestructure graph for an aquar-ium of fish or cage of mice thatyou have in your classroom.Discuss what the graph mayreveal about expected popula-tion growth.

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rate for each period of time. (Note: Theannual percent growth rate is actuallyfor a span of many years rather thanonly one year.)

7. The human population continues toshow an increase in its annual growthrate and has not yet reached its carryingcapacity.

Knowledge Have students writethree questions about this lab and quiz eachother. Use the Performance Assessment Listfor Asking Questions in PASC, p. 19. L2

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Section Focus Trans-parency 9 and Master

BioLab and MiniLab Work-sheets, p. 18

Content Mastery, p. 17, 19-20

Reinforcement and StudyGuide, pp. 17-18 L2

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5. Shake the bag. Without lookinginto the bag, reach in and remove30 beans.

6. Record the number of markedbeans (recaught and marked) andthe number of unmarked beans(caught and unmarked) in yourdata table as trial 1.

7. Return all the beans to the bag. 8. Repeat steps 5 to 7 four more

times for trials 2 to 5.9. Calculate averages for each of the

columns. 10. Using average values, calculate

the original size of the bean pop-ulation in the bag by using thefollowing formula:M = number initially markedCwM = average number caught

during the trials with marksCw/oM = average number caught

during the trials without marks

11. Record the calculated populationsize in the data table.

12. To verify the actual populationsize, count the total number ofbeans in the bag and record thisvalue in the data table.

1. Thinking Critically This experi-ment is a simulation. Explain whythis type of activity is best done asa simulation.

2. Applying Concepts Give anexample of how this techniquecould actually be used by a scientist.

3. Analyzing Data Compare thecalculated to the actual popula-tion size. Explain why they maynot agree exactly. What changesto the procedure would improvethe accuracy of the activity?

4. Making Inferences Explain whythis technique is used more oftenwith animals than with plantswhen calculating population size.

5. Making Predictions Assume youwere doing this experiment withliving animals. What would yoube doing in step 2? Step 3? Step 5?

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

4.2 HUMAN POPULATION GROWTH 109

Going FurtherGoing Further

Writing about Biology Assume that youare a field biologist on Mackinaw Island,Michigan. Explain in detail how you wouldgo about determining the deer populationon the island. Include a data table thatcould be used in your procedure.

To find out more about populations of organ-

isms, visit the Glencoe Science Web site. science.glencoe.com

=Calculated Population Size

M � (CwM + Cw/oM)CwM

TrialTotal caught

1

2

3

4

5

Averages

Calculated population size = ______

Actual population size = ______

30

30

30

30

30

30

Number caught with marks

Number caught without marks

Data Table

BIOLOGY


1. Students may note that it’sdifficult to obtain enoughtraps, find a suitable site forstudy, and work with trappedanimals.

2. Possible answers: to deter-mine the size of a populationin a specific area, such as anational park, or to measure achange in a population sizeover time

3. The calculated value is basedon counting a representationof the population, not everyindividual in the population.To increase the accuracy ofthe activity, one couldincrease the number of trials,the number of animals re-caught, or the number of ani-mals caught and marked.

4. Plants do not move about andso are easier to count.

5. Step 2, capture animals incages; step 3, tag or mark theanimals in some manner; step5, reset traps and capturemore animals

Skill Provide students withraw data and have them calculatethe size of a population. Use thePerformance Task AssessmentList for Using Math in Science inPASC, p. 29. L3

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ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

109

Going FurtherGoing Further

Have students design a long-term experiment that woulddetermine the effectiveness of a“roach motel” on reducing thesize of a cockroach population.

How can you determine thesize of an animal population?


ProblemHow can you model a measuring

technique to determine the size of ananimal population?

ObjectivesIn this BioLab, you will:■ Model the procedure used to

measure an animal population.■ Collect data on a modeled animal

population.■ Calculate the size of a modeled

animal population.

Materialspaper bag containing beansmagic markercalculator (optional)

Safety PrecautionsAlways wear goggles in the lab.

Wash hands after working with plant material.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

PREPARATIONPREPARATION

PROCEDUREPROCEDURE

S cientists can determine the number of animals in a large population byusing a sampling technique. Here is how it works. They trap and mark

a few animals in a specified area. The animals are released and the traps arereset. Among the animals caught this second time, some are marked andsome are unmarked. Scientists then calculate the total population for theirspecified area based on the ratio of marked animals to unmarked animals.

In this activity, a bag represents the area of land where the populationstudy is being conducted. Beans will represent animals. All the beans in thebag represent the total animal population being studied.

1. Copy the data table.2. Reach into your bag and remove

20 beans. 3. Use a dark magic marker to color

these beans. These will representyour caught and marked animals.

4. When the ink has dried, returnthe beans to the bag.


Time AllotmentOne class period

Process Skillsapply concepts, collect data,experiment, formulate models,interpret data, predict, use num-bers, write about biology

Safety PrecautionsHave students wash their handsafter handling the bean seeds.

■ Prepare bags in advance. Place150-175 beans in each bag.

■ Shortcut to counting beans—count out 165 beans. Thendetermine the volume of thisnumber of beans by placingthem into a graduated cylin-der. Read the volume and usethis as a guide in preparing theother bags. All bags DO NOThave to have the same numberof beans.

■ Remove all marked beans fromthe bag at the end of each classand replace with unmarkedbeans.

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PROCEDUREPROCEDURE

Teaching Strategies■ Do not tell students the total number ofbeans in each bag.■ Any type of marker is suitable. Make surethe color contrasts with the bean color.Make sure all sides of the bean are colored.■ The number of beans removed in step 5does not have to be exactly 30 but should beclose.

■ Review the technique for calculating anaverage.

Data and ObservationsSample data may appear as shown on page109.

TrialTotal

caught

Totals

Average

30

30

30

30

30

150

30

Number caughtwith marks

Number caughtwithout marks

Data Table

150

160

3

2

5

4

6

20

4

27

28

25

26

24

130

26

1

2

3

4

5 Calculated population size = ______

Actual population size = ______

(This number will vary per bag.)


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Chapter 4 AssessmentChapter 4 Assessment

SUMMARYSUMMARY

Section 4.1

Section 4.2

Main Ideas■ Some populations grow exponentially until they

reach the carrying capacity of the environment.Populations may exhibit slow growth that tendsto approach the carrying capacity with minorfluctuations, rapid growth that tends to expandexponentially and then experiences massivediebacks, or fall somewhere in between.

■ Density-dependent factors such as disease andfood supply, and density-independent factorssuch as weather, have effects on population size.Interactions among organisms such as preda-tion, competition, stress, and crowding alsolimit population size.

Vocabularycarrying capacity (p. 97)density-dependent

factor (p. 100)density-independent

factor (p. 101)exponential growth

(p. 97)

PopulationDynamics

Main Ideas■ Demography is the study of population charac-

teristics, such as growth rate, age structure, andmovement of individuals. Birthrate, death rate,and fertility differ considerably among differentcountries, resulting in uneven populationgrowth patterns across the world.

Vocabularyage structure (p. 106)demography (p. 104)emigration (p. 107)immigration (p. 106)

HumanPopulationGrowth

CHAPTER 4 ASSESSMENT 111

1. Which of the following factors is density-dependent?a. drought c. foodb. flood d. wind speed

2. When populations increase, resource deple-tion may result in ________.a. exponential growthb. straight-line growthc. competitiond. increase in predators

3. Storms, cold temperatures, and drought areall ________.a. density dependentb. biotic factorsc. exponentiald. density independent

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS 4. Between A.D. 1 and A.D. 1650, the world’spopulation had a major dip because of________.a. fertilityb. decreased death ratec. density-independent factorsd. bubonic plague

5. Which of the following environments wouldbe more likely to have organisms that exhibitfast growth?a. hot desertsb. large, deep lakesc. prairies that often floodd. tropical rain forests

6. A female’s fertility rate is the number of offspring she produces ________.a. in a year c. by age 50b. in a decade d. over her lifetime

111



Chapter Assessment, pp. 19-24MindJogger VideoquizzesExamView® Pro SoftwareBDOL Interactive CD-ROM, Chapter

4 quiz

Main IdeasSummary statements can be used bystudents to review the major con-cepts of the chapter.

Using the VocabularyTo reinforce chapter vocabulary, usethe Content Mastery Booklet andthe activities in the Interactive Tutorfor Biology: The Dynamics of Life onthe Glencoe Science Web site.science.glencoe.com

1. c2. c3. d4. d5. c6. d

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS

All ChapterAssessment

questions and answers have beenvalidated for accuracy and suitabil-ity by The Princeton Review.

VIDEOTAPEMindJogger Videoquizzes

Chapter 4: Population BiologyHave students work in groups as they playthe videoquiz game to review key chapterconcepts.

Polymerization is a process in which singlemolecules known as monomers are joined

to form long chains called polymers.Polystyrene is a petrochemical polymer.

Manufacturers of this plastic argue that it has revolutionized many industries, especially those related to food service.

Environmentalists contend that this plastic,like many others, is a dangerous substance

that harms Earth and its inhabitants.

The basic chemical unit, or monomer, ofpolystyrene is styrene. Pure polystyrene is

brittle, but by combining styrene with othermonomers, an impact-resistant plastic is formed.Polystyrene is commonly used as building insula-tion and flotation devices, as packaging materials,and to make a wide assortment of disposablecups, plates, bowls, containers, and cutlery.

Foamed plastics Foamed plastics, often used infood packaging, are made by blowing tiny holesinto a polymer. Polystyrene was the first foamedplastic developed. Initially, chlorofluorocarbons,or CFCs, were used as blowing agents to pro-duce this closed-cell foam in which gas cells arecompletely isolated from each other by thin wallsof plastic. Today, most foamed polystyrene ismade using pentane or carbon dioxide as theblowing agent. Unlike CFCs, these gases do notdestroy Earth’s ozone layer.

Polystyrene products Foam beverage cups andplates, plastic forks, some packaging “peanuts,”and the jewel cases that house compact discs area few of the many polystyrene products on themarket today. In the food service industry, poly-styrene products are touted for their safetybecause they are used only once and thrownaway. Because of its insulating properties, foamedpolystyrene keeps hot foods hot and cold foodscold, thus reducing the risk of contamination

by bacteria. Foam packaging peanuts and poly-styrene blocks protect electronics and other fragile items during shipping.

The perils of polystyrene Despite its conve-nience and popularity in various industries, polystyrene poses its share of environmental concerns. The main monomer in this plastic—styrene—is classified as a neurotoxin, as itimpairs the central and peripheral nervous systems. Long-term exposure to even smallamounts of styrene can also cause abnormalhematological, lymphatic, and cytogeneticeffects. People do not eat plastic containers, butstudies have shown that styrene is common inhuman fat tissue because it is often leached fromfoods and beverages stored, eaten, and drunkfrom such containers.


ConnectionChemistryChemistry

Connection Polystyrene: Friend or Foe?

Polystyrene makes up less than 1 percent of ourwaste by weight, yet it constitutes 25-30 percentby volume. What does this say about the averageconsumer in this country? Also, polystyrene doesnot degrade in landfills. Suggest two reasons whythis is both a good thing and a bad thing.

To find out more about plastics, visit the Glencoe

Science Web site. science.glencoe.com

CONNECTION TO BIOLOGYCONNECTION TO BIOLOGY

BIOLOGY

110

Purpose Students will find out someadvantages and disadvantages of acommonly used plastic calledpolystyrene.

Teaching Strategies■ Use a dozen colored, plastic-coated paper clips to demonstratehow monomers link to formpolymers. Make a chain with twoalternating colors. Have a volun-teer identify the monomers. Iftime allows, have students con-sult basic chemistry books tomake models of complex plasticpolymers.■ Have students survey plasticcontainers at home or at stores todetermine some of the many usesof polystyrene. Inform them thatplastics labeled with the number“6” are polystyrene. Compile amaster list of uses, which mightinclude yogurt, cottage cheese,and sour cream containers;audiocassette boxes; frozen din-ner trays; toy parts; picnic table-ware; and others.■ Have students suggest severalsituations in which disposabletableware would benefit thoseusing it. Answers might include inhospitals, where the transmission ofpathogens can be a problem topatients, especially those withimmunodeficiency diseases, or inschool cafeterias, where cleaningreusable dishes, glasses, and cutlerymight be cost prohibitive.

Connection to BiologyMany environmentalists in thisnation, as well as people in otherWestern cultures, view Americansas a “throw-away” society basedon their widespread use of plasticsand dependence on single-usecontainers and tableware items.The advantage of polystyrenebeing nondegradable is that harm-ful substances are kept from enter-ing the environment. The disad-vantage is that this material takesup valuable space in landfills.

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ConnectionChemistryChemistry

Connection

Note Internet addresses that you find useful in the space belowfor quick reference.

BIOLOGY




CHAPTER 4 ASSESSMENT 113

21. Which environmental factors would mostaffect the populations of developing countries?

22. As human populations grow, what might happen to the populations of other species?Discuss the causes for your hypotheses.

23. Assume that a female black rat gives birthevery month and produces eight young. Ineach litter, four are female and four are male.Starting in month zero with one newborn lit-ter of four males and four females for a totalpopulation of eight, calculate the total popu-lation size at months 1, 2, and 3.

24. Observing and Inferring Why are short life-history species, such as mosquitoes and someweeds, successful even though they oftenexperience massive population declines?

25. Comparing and Contrasting Compare andcontrast the characteristics of species havinglong life-history patterns with those that haveshort life-history patterns.

26. Concept Mapping Complete the conceptmap by using the following vocabulary terms:density-dependent factors, density-indepen-dent factors, exponential growth, immigration.

THINKING CRITICALLYTHINKING CRITICALLY

APPLYING MAIN IDEASAPPLYING MAIN IDEAS ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

The following bar graph indicates the num-ber of dandelions counted by five groups ofstudents (groups A-E) on school grounds.Assume that the school grounds have 21 950square meters planted in grass.

Interpreting Data Use the graph to answerthe following questions.1. How many dandelions per square meter

did group A count?a. one c. threeb. two d. four

2. On average, how many dandelions didthe students count per square meter?a. one c. threeb. two d. four

3. Using the average number of dandelionsper square meter, what is the estimatednumber of dandelions on the schoolgrounds?a. 21 950 c. 50 485b. 43 900 d. 65 850

4. Interpreting Data The study isrepeated two months later and now theaverage is five dandelions per squaremeter. Now, what is the estimated sizeof the population?

For additional review, use the assessmentoptions for this chapter found on the Biology: TheDynamics of Life Interactive CD-ROM and on theGlencoe Science Web site.science.glencoe.com

CD-ROM

Groups

Num

ber p

er sq

uare

met

er

A B C D E

1

0

2

3

Dandelion Population

2.

1.

such as

3.

4.

is limited by

113

21. density-dependent factors suchas limited food or water andincreased chances for disease tospread

22. The populations of otherspecies may decrease. Humansmay disrupt the habitats ofother species, so that they donot have enough space for mat-ing, rearing offspring, or find-ing shelter and food.

23. Month one = 8 parents + (4females times 8 offspring) = 40.Month two = 40 parents + (20females times 8 offspring) =200. Month three = 200 parents+ (100 females times 8 off-spring) = 1000.

24. Short life-history species pro-vide enough potential offspringin the form of seeds, eggs, orlarvae to produce the next gen-eration, even when there aremassive die-offs.

25. Species with long life-historiesusually have few young thattake a long time to mature,while those species with shortlife-histories have many off-spring that mature quickly.

26. 1. Exponential growth; 2.Density-independent factors; 3.Density-dependent factors; 4.Immigration

THINKING CRITICALLYTHINKING CRITICALLY

APPLYING MAIN IDEASAPPLYING MAIN IDEAS


1. c2. b3. b4. 109 750


7. According to the graph, the growth rate of ahouse fly population ________.a. increases, then drops suddenlyb. increases, at a steady ratec. increases rapidlyd. levels off after a certain amount of time

8. A person breeds rabbits in a cage. After a few generations, she observes that the rabbitsare more aggressive towards each other, theyoung are less healthy, and more young rabbits die. This population is:a. under stressb. under the carrying capacityc. density independentd. both choices a and c

9. A life-history pattern that tends to approachcarrying capacity with minor fluctuations is________.a. population dependentb. slow growthc. fast growthd. exhibited by most insects

10. What can be said about the growth of acountry with an age structure graph thatapproximates a rectangle?a. It is decreasing.b. It is increasing slowly.c. It is stable.d. It is increasing rapidly.

11. A J-shaped growth curve indicates a popula-tion is experiencing ________ ________.

12. The highest level at which a population canbe sustained is its ________ ________.

13. Population growth rates are affected by________ and ________ rates. It is also influ-enced by immigration and ________.

14. Predators that help control the size of a population represent a ________.

15. From Table 4.2, the fastest growing countryis ________. The women of ________ givebirth to the most children.

16. The solid-line graph below shows thechanges in deer population over time. Thedotted line represents the ________ ________for the deer population.

17. A person who studies human populationgrowth characteristics is a ________.

18. A bacterial cell divides every 30 minutes andproduces two cells. Starting with one cell,after 30 minutes there would be two cells,after 60 minutes ________ cells, and after 90minutes, ________ cells.

19. A demographic estimate of how long a per-son of a particular age will live is calledhis/her ________ ________. In the UnitedStates, this estimate ________ every year.

20. Populations that grow without restriction areexperiencing ________ ________.

112 CHAPTER 4 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

Pace Yourself Many test questions look more complicated thanthey really are. If you find yourself having to do agreat deal of work to answer a question, take asecond look and consider whether there might bea simpler way to find the answer.

Num

ber

of d

eer

Time

Deer Population Over Time

Popu

latio

n siz

e

Time

Population Growth of Houseflies

1000

500

100

112

7. c8. a 9. b

10. c11. exponential growth12. carrying capacity13. birth, death, emigration14. limiting factor15. Jordan, Uganda16. carrying capacity17. demographer18. 4, 819. life expectancy, increases20. exponential growth



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