2013

EcologyUnit:PopulationGrowth

Activities

Written byMrs.Engelbrecht

Adapted by Mary Beth Armstrong

MCHSBiology

20102011

©TerieR.Engelbrecht,2010

Ecology—PopulationGrowth

Objective2

2A.I canclassifyexamplesoffactorsthatlimitapopulation’sgrowthaseitherdensity-independentor density-dependent.

2B.Icanpredictwhatwillhappentoapopulation’ssizeifthefollowingoccur:emigration, immigration,changesinbirthratesanddeathrates.

2C.Icaninterprettwodifferentgraphsofpopulationgrowth:exponentialpopulationgrowthand logisticpopulationgrowth.

VocabularyPractice
Population density
density-independentfactor density-dependentfactor emigration / Limiting factor
Immigration
competition
predation / exponentialpopulationgrowth logisticpopulationgrowth carryingcapacity
VocabularyCards

A.Get11 indexcards—oneforeachofthevocabularywordsabove.Splitonesideofeach cardtomakeitlooklikethediagrambelow.Writeeachwordaboveinthecenterboxofeach card.Then,foreachword,writewhatisineachboxforeachword.You mayusemarkersor coloredpencilstomakeyourvocabularycardsaestheticallypleasing.Useyourtextbook, an online dictionary,oradictionarytohelpyou.

Bookdefinition Yourdefinitioninyourownwords

WORD

Pictureoftheword (Word)isNOT

because .

B.Layallofyourvocabularycardsoutonyourdesk.Decidewhichwordsgotogether(are connected).Putthemintogroupsbymovingthosewordsnear eachotheronyourdesk.

C.Foreachgroupyoumade,getablankindexcard.Foreachgroup,writeWHYthosewords gotogether(acategoryname)onablankcard,andplaceitaboveeachgroup.

D.OnaseparatesheetofpaperandUSINGALLOFTHEWORDS, make a concept map showing howallofthe wordsareconnected. Useyourcategoriestohelp youconnectthegroupsofwords,andthen writeconnectionsbetweenEACHword. Keepthismap;you’llneeditafterthereadingactivitythatfollows.

ReadingForUnderstanding—Practice

A.Readthetrulyrivetingpassagebelowaboutpopulationgrowth.If,whilereading,youareaskedtodo something,thendoit.

B.Asyouarereading,underlineanydefinitionsofvocabularywordsyoufind.Changeyour vocabularycardsifyou needtoifyourealizeyougotsomethingwrongonyourcardsasyouread.

C.Markthefollowingasyouread:

DGT=Idon’tgetthis.Ihadtore-readthistotryandunderstandit.

!!=Iamsurprisedtofindthisout

??=Ihaveaquestionaboutthis(writeyourquestioninthemargin)

D.Discusswhatyoumarkedand anychangesyoumade to a partner (if one in available) after reading the passagebelow.Have yourpartnerhelpyou to answeryourquestionsandclarify whatyoudon’tget.

TheUpsandDownsofPopulationGrowth

Apopulationisa groupoforganismsofthesamespeciesthatlive ina certainarea. Ecologistsregularlymonitorthenumberoforganismsinmanypopulations,butwhydotheydo this? Why dowecareifthenumberoforganismsin anareaisgrowingorshrinking?Well, populationsthataregrowingandshrinkingcanbeindicatorsofpotentialproblemsoccurringin theorganisms’environment,andgivesecologistsa“headsup”ifsomethingisgoingwrong.But itisnotenoughtosimplyknowifthenumberoforganismsinanareaisgoinguporgoing

down;ecologistsneedtoknowwhythenumberoforganismsisfluctuating. So,oneofthe mainquestionsecologistsaskthemselvesisthis:Whyisa population’ssizeisgoinguporgoing down?

Therearemanyfactorsthatcancausea population’ssizetochange. Butfirst,youmust understandthebasicreasonsbehindwhyapopulationgrowsorshrinks.Anypopulation, whetheritbehumans,chipmunks,themoldgrowingonbread,orthebacterialivinginyour intestines,willgrowifmoreorganismsarebeingcreated,orborn,thanaredying. Ifa populationhasmoreorganismsdyingthanarebeingborn,thenthepopulationwillshrink. The numberofbirthsina populationiscalledthebirthrate(alsoreferredtoasnatality). The numberoforganismsthataredyingina populationiscalledthedeathrate(also referredtoas mortality). Thus,ifthebirthrateisgreaterthanthedeathrate,a populationwillgrow.Ifthe deathrateisgreaterthanthebirthrate,thenthepopulationwilldecreaseinsize.

StopandThink#1 / :
a)Thehumanpopulationiscurrentlygrowingatanexponentialrate. Whatdoesthismean aboutourbirthanddeathrates?
b)TheMantledHowlerMonkey(foundinMexicoandSouthAmerica)iscurrentlyconsideredan endangeredspecies. Whatdoesthismeanaboutitsbirthanddeathrates?

While populationswouldprobablyliketocontinuetogrowinsize,a populationof organismscannotgrowforever—itsgrowthwillbelimited,orstopped,atsomepoint,andthe deathratewillbegreaterthanthebirthrate. Apopulation’sgrowthislimitedbytwogeneral factors:density-independentfactorsanddensity-dependentfactors. Whyarethesefactors namedinsuchacomplicatedway?Well,actually,thesenamesaren’tas complicatedas they seem;infact, theycanevenhelpyourememberwhateachofthetermsmeans.

Tounderstandwhyscientistsnamedthesefactorsinthewaytheydid,youmustfirst understandtheconceptofpopulationdensity. Apopulation’sdensityisNOTwhetherornot thepopulationwillfloatorsink(theywouldprobablysink...resultingina lotoftragic,needless organismdeaths). Populationdensityreferstohowmanyorganismsthereareinoneparticular spot. Ifa population’sdensityisveryhigh,thatmeanstherearea lotoforganismscrowded

intoacertainarea. Ifapopulation’sdensityislow,thatmeansthereareveryfeworganismsin anarea.

Nowthatyouknowaboutpopulationdensity,wecantalkaboutthedifferencebetween thetwotypesoflimitingfactors. Ifa factorthatstopsapopulation’sgrowthisinfluencedby

thepopulation’sdensity,thenitiscalleda density-dependentlimitingfactor. Ifthe population’sdensitydoesnotinfluencewhetherornotthefactorstopsthepopulation’s growth,thenitiscalleda density-independentlimitingfactor.

StopandThink#2 / :Imagineapopulationofskunks. Yes,skunks. Imaginethat theskunksare
reproducingataveryhighrate,andtheskunkpopulationisgrowing rapidly—especiallyinthe
fieldbehindMrs.E’shouse.
a)Listapossibledensity-independentfactorthatcouldstoptheskunkpopulation’sgrowth. b)Listapossibledensity-dependent factorthatwouldlimittheskunkpopulation’sgrowth.
Reviseyouranswersasyoureadmoreaboutdensity-independentlimitingfactorsanddensity- dependentlimitingfactors

Density-independentlimitingfactorsthatcanstopa populationfromgrowingcanbe such thingsasnaturaldisasters,temperature,sunlight,andtheactivitiesofhumansinthe environment. Naturaldisasterssuchastornadoes,floods,andfireswillstopa populationfrom growingnomatterhowmanyorganismsarelivingina certainarea. Thesamegoesforthe temperatureofanareaandtheamountofsunlightanareareceives—if thetemperature increasesduetoglobalwarming,oriftheashkicked upintotheatmosphere fromanasteroid smashingintotheearthblocksoutalotofsunlightfora fewdecades,thesewillbothcausea decreaseina population’snumbers,nomatterhowlargeorsmallthepopulationwastobegin with. Humanactivitiesthataltertheenvironmentwillalsodecreasetheamountoforganisms ina population,nomatterthesizeofthepopulation.

Density-dependentlimitingfactorscomeintoplaywhena populationreachesacertain numberoforganisms. Thusthenumberoforganismsinthepopulationmatterswhentalking aboutdensity-dependentlimitingfactors. Forexample,whenapopulationreachesacertain size,therewon’tbeenoughresources(food,shelter,water)foralloftheorganisms. Thiscould causethepopulationtostopgrowingwhenitreachesthemaximumnumberoforganismsthat canbesupported,or“carried,”bytheenvironment. Thisnumberisknownas thepopulation’s carryingcapacity. Eachpopulationoforganismshasa differentcarryingcapacity,depending ontheareainwhichitlivesandtheamountofresourcesavailableinthatarea. Belowisa graphofarabbitpopulationthathasreacheditscarryingcapacity:

Thistypeofpopulationgrowthiscalledlogisticpopulationgrowth;itrepresents whatactually occursasa population’snumbersgettoolargefortheenvironmenttosupportit. While the numberofrabbitsinthepopulationincreasedrapidlyatfirst,itsgrowthbegantoslowdown towardstheendofAugust. Oncethepopulationnumbersleveledoff,roughlyequalnumbers ofrabbitsweredyingas beingborn.

StopandThink#3 / : Studythegraphonthepreviouspagecarefully.
a)Whatistherabbitpopulation’scarryingcapacity?
b)Thepopulationofrabbitsbetweenmid-Mayandmid-Juneisgrowing asfastas:(circleone)
aturtlewalking(superslow.) astudentrunninglatetoclass(fast!)
youwalkingtoclass(slow.) Mrs.Erunningawayfromamountainlion(superfast!)
c)Whataboutthegraphledyoutocircletheansweryouchoseinletterb?
Reviseyouranswers(ifnecessary)asyouread moreaboutpopulationgrowth.

Beforea populationreachesitscarrycapacity,itexperiencesaperiodofrapidgrowth. Thisperiodofgrowthiscalledexponentialpopulationgrowth,because,mathematically,the populationisaddingorganismsatanexponentialrate. Duringthistimeperiod,thereareplenty ofresourcesavailableforallorganisms,so moreorganismsarebeingbornthanaredying.The graphforexponentialpopulationgrowthlooks sortoflike thegraphforlogisticpopulation growth,onlywithouttheflat“levelingoff”lineattheendofit:

StopandThink#4 / :
a)Fillinthedifferenceschartbelow:
density-independent limitingfactor / density-dependentlimitingfactor
logisticpopulationgrowth / exponentialpopulationgrowth
b)Thehumanpopulationiscurrentlygrowingatanexponentialrate.Sinceyouhavelearned thatpopulationscannotgrowforever,whataresomethings(morethanone!)thatcouldhappen whenthehumanpopulationreachesitscarryingcapacity?
Reviseyouranswersasyoureadfurther,ifnecessary.

Theamountofresourcesisnottheonlylimitingfactorthatdependsona population’s density. Diseasesandparasitescanlimitapopulation’sgrowthoncethepopulationreachesa certainnumberoforganisms. Themoreorganismsthereare,thefastera diseasecanspreador aparasitecanbetransferredtoanotherorganismbecausetherearemoreavailablehoststhat areneareachother. Competitionforresources—eitherbetweenthesamespeciesortwo differentspecies—willalsodecreasea population’ssize.Resourcesarelimitedinanyhabitat, and,whenpopulationsreachacertainsize,therewillnotbeenoughtogoaround. Whentwo organismsinthesamehabitataretryingtousethesameresource,theyarecompetingforthat resource. Whicheverorganismhasthebetteradaptationstoobtainthatresourcewillbeable toreproducemoreoften,andtheirpopulationwillgrow.Theorganismthatisnotsuccessfulat competingfortheresourcewillnotreproduceas often,andtheirpopulationwilldecrease.

Predationisanotherdensity-dependentlimitingfactorseeninpopulations. Whenlots ofpreyisavailable,predatorswilleattheprey,haveenergytoreproduce,andtheirnumberswillincrease. Thepopulationoftheirpreywillbegintodecreaseasmoreandmoreofthemare eaten. However,thepredatorpopulationwilleventuallyreachcarryingcapacity—therewill

notbeenoughpreyforallofthepredatorsinthepopulation,sincethepredatorsthemselves arecompetingfortheir“prey”resource. Asthenumberofpreydecreases,sowillthenumber ofpredators,becausethereisn’tenoughfoodtogoaround. Asthenumberofpredators decreases,thatmeanstheprey havetimetoreproduceandincreasetheirpopulation. Thus,

predator-preypopulationsgothroughcycles ofpopulationgrowth,whichisshowninthegraph belowbetweenlynx(predator)andsnowshoehares(prey):

You will need to go to a computer in the classroom or go to the library to complete the activity above. Just click the link and complete the activity. Print the note/summary page at the end and complete it.

StopandThink#5 / :
a)Pretendthegraphonthepreviouspageisthedatayouobtainedafterdoingyourownlab, andyouarefillingoutthelabwrite-upform.Yougettothepartoftheformwhereyouhaveto filloutyourresultssentence. Usingthedatainthegraphtoguideyou,fillouttheresults sentencebelow:
Asthenumberoflynxincreases,thenumberofsnowshoehares: . b)Usingwhatyouknowfromthereadingandfromthegraph,give a scientific explanationfor
theresultssentenceyoucompletedabove. (Remember: a“2”is simplyrepeatingwhat’sinthereading.
A“3”wouldinvolveusingwhat’sinthereadingandusingthegraphaboveas anexample. A“4”wouldinvolve usingwhat’sinthereading,usingthegraphabovetohelpyouexplain it,andgivinganewexampleorananalogy.)
Ascientific explanationfortheseresultsis:

Onelastdensity-dependentlimitingfactorthatstopsa populationfromgrowingis emigration. Emigrationoccurswhen,asa populationapproachescarrying capacity,individual organismsfrom thepopulationleaveandgotoanewareawheretheycanfindenough resourcesforsurvivalandreproduction. This,obviously,willcauseadecreaseintheamountof organismsina population. Youmayhaveheardofawordthathastheexactoppositemeaning andeffectonpopulationsize—immigration.

StopThink#6:

a)Knowingthatimmigrationistheoppositeofemigration,whatdoesimmigrationmean?

b)Willimmigrationcausepopulationstoincreaseordecreaseinsize?

c)UsingMarengoas anexample,giveanexampleofimmigrationandemigration’seffectson thepopulationofhumansinMarengo.

MakingConnections—Understanding HowWordsConceptsFitTogether

A.ChooseONEoftheoptionsbelow:

1.Make/reviseaconceptmaponcopypaperthatincludesALLofthewords.Makesureit hasacentralidea,includesallthewords,andhas allconnectorslabeled.

A“2”willshowmeyoujustknowwhatthewordsmean.A“3”willshowmeyouknow whatthewordsmean,andunderstandthebasicconnectionsbetweenallthewords.

A“4”willshowmewhata“3”does,butwillalsoaddwords,examples,oranalogiesto demonstrateanin-depthmasteryoftheconcepts.

2.Getablankjigsawpuzzle.Chooseeitheralevel“3”understandingpuzzle,oralevel

“4” understandingpuzzle.

Usingallthewords,writethewordsinthepuzzlepieces.Ifyouplacetwoor morewordsnexttoeachother,theymusthaveaconnection!

Writethe connectionsbetweenthe wordsalongthebordersbetweentwo connectedjigsawpuzzlepieces.

Drawapictureofeachwordinitspuzzlepiece.

WorkingTowardsMasteringtheICanStatements—Practice

1.Readeachsituationinthechartbelow.Then,stateifthe exampleisadensity-independent limiting factororadensity-dependent limitingfactor. Then,statethespecificlimitingfactorthatis occurring.Thefirstoneisdoneforyouasanexample.

Situation / Density-
independent, ordensity- dependent? / Limiting
Factor:
Mrs.Engelbrechthas32studentsassignedtoherBiology
class,butsheonlyhasroomfor28.Becausetheroomis socrowded,theextra4studentsleavetheroomtogoto Guidanceandhavetheirscheduleschanged. / density-dependent / emigration
Northernpike(it’safish)feedonanotherfish,the
yellowperch.Anincreaseintheyellowperch populationcausesanincreaseinthenorthernpike population.
TheBPoilspillintheGulfofMexicohasharmedmany
aquaticorganismsthatliveintheGulfregion.
Anewstrainofinfluenza(theflu)breaksoutinNew
YorkCity.
Apopulationofrabbitsandapopulationofdeerareboth
feedingoffthesameplantsinthesamehabitat.
HurricaneKatrinaforcedthousandsofpeopletoleave
NewOrleans.
65millionyearsago,alargeasteroidcollidedwiththe
Earth. Asaresult,largeamountsofashwereejectedinto
Earth’satmosphere.
Duetohumansputtingincreasingamountofgreenhouse
gasesintothe atmosphereandcuttingdowntreesthat wouldnormallytakeupsomeofthosegases,theEarth slowlygetswarmerandchangesclimatesaroundthe globe.

2.Studythegraphbelow:

a.Whichcountrylookslikeitisexperiencingexponentialgrowth?

b.Whichcountrylookslikeithasreacheditscarryingcapacity?

Becauseithasreached itscarryingcapacity,describetherelationshipbetweenitsbirth ratesanddeathratesinthespacebelow:

c.DescribewhatishappeningtoEurope’spopulationsizeintermsofbirth ratesanddeath rates.

d.Whichcountryorcountriescouldbeexperiencing:

•emigration:

Explainyouranswershere:

•immigration:

Explainyouranswershere:

3.ReadtheCAUSEonthelefthandsideofthetablebelow.Then,predicttheEFFECTofthe causeintheright-handcolumn.Forthelastone,fillintheCAUSEportionofthetable.

CAUSE / EFFECT
Duringthe1920s,manyEasternEuropean
peopleleavetheircountriestocometothe
UnitedStates.
Duringthe1920’s,manyEasternEuropean
peopleentertheUnitedStates.
Manymorebabieswereborninthepost-
WorldWarIIerathaninthepre-WorldWar
IIera.
Chinaimposeda“onechildonly”policyin
1979whichisstillineffecttoday.
Seals arehuntedfortheirmeatandfurinsome
regions,resultinginmanydeathsofseals.

Havesomeextra timeandwanttoseeifyoucandothisata“4”?Youcould dothefollowingin thespacebelow:

A.Dosomeresearchandlookupotherexamplesof immigration,emigration,andhowbirthanddeathratesaffectpopulationgrowth. Then, constructyourOWNchartjustliketheoneabove.

B.DothesamethingasletterA,onlythistimecreateachartwheretheEFFECTSarefilledin, andsomeoneelsehastocomeupwiththeCAUSES.

**Ifyouhavetimetodo eitherofthese,showthemtoyourinstructor.

4. Graph Ishows thegrowth curveforacultureofParamecium aurelia,a typeofmicroscopic, unicellular protist.Graph IIshows the growthcurveforacultureofParameciumcaudatum,a larger speciesof the sameprotist. Graph IIIshows thegrowth curvesofboth specieswhentheyare grown together.

a.WhattypeofpopulationgrowthisshowninGraphsIandII,wheneachprotistisinitsown jar?

Explainhowyouknow:

b.StudyGraphIII(thebottomgraph)verycarefully.Itshowswhathappenswhenyouput bothpopulationsofparameciainthesamejar.

WhydidthepopulationofP.caudatumdecrease,butthepopulationofP.aureliaincrease?

Lookatyouranswerabove.Gobackandaddifwhatoccurredwasadensity-independent limitingfactor,oradensity-dependentlimitingfactor. Then,explainwhyitisthefactoryou chose.

5.Goto a computer either in the classroom or in the library.Use a programlike Excel toconstructagraphofthedatabelow:

a.Whattypeofgrowthisshownbythiswhite-taileddeerpopulation?

Explainhowyouknow:

b.Whatisthewhite-taileddeer’scarryingcapacity? (Givetherangethatitfallsinto): Between and .

c.Predictwhatcouldbecausingthewhite-taileddeerpopulationtoreach itscarryingcapacity:

d.AdjustthedatafortheSPRINGsothat thegraphofthatdatalookslikeagraphof exponentialpopulationgrowth. Showyourgraphtoyourinstructorbeforemovingon.

6.Filloutthedifferenceschartbelow.Makesureyourdifferencesarespecificenoughtotellme thatyoutrulyunderstand,butdon’twritemeanovel.Also,makesure yourdifferencesmatch!

birthrate / deathrate
density-independent limitingfactor / density-dependentlimitingfactor
Afarmersprayingcropswithpesticides / Necrotizingfasciitis(whatyougetifyoucome
incontactwithflesh-eatingbacteria)
exponentialpopulationgrowth / logisticpopulationgrowth

Level4ThinkingPractice

Writeanalogiesforthewordsbelow.Remember,analogiestaketwoseemingly unrelatedthings andmakeaconnectionbetweenthem. Thinkoutsidethe“sciencebox”forthese!

a.Density-independentlimitingfactorsarelike: because

.

b.Density-dependent limitingfactorsarelike: because

.

c.Exponentialpopulationgrowthislike because

.

d.Logisticpopulationgrowthislike because

.

DemonstratingMasteryoftheICanStatements

Scoreyourselfonhowwellyouhavemasteredthe“Icanstatements”usingtherubricbelow:

PopulationGrowth / 0=No
evidence / 1=
Beginning / 2=
Progressing / 3=
Proficient / 4=
Advanced
2A.I canclassifyexamplesof factorsthatlimitapopulation’s growthaseitherdensity- independentordensity- dependent.
2B.Icanpredictwhatwill happentoapopulation’ssizeif thefollowing occur:
emigration,immigration, changesinbirthratesand deathrates.
2C.Icaninterprettwo differentgraphsofpopulation growth:exponential populationgrowthandlogistic populationgrowth.

1)TaketheExitTicketprovidedbyyourinstructor.

2) Checkyouranswerswhenyouarefinished.

3)Markwhateveryoudidnotgetcorrectonyourexitticket.

4)Re-rateyourselfonhowwellyouhavemasteredtheIcanstatementsin therubricabove.

5)StaplethispagetothebackofyourExitTicket..