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Clipbirds*
Thishands‐onactivityallowsstudentstoexperiencevariationwithinapopulationandtheeffectof
selectionpressureonthepopulation.WhichvariationsareadvantageousforsurvivalandreproductioninEastClipland?InWestClipland?
Evolutionistheresultofnaturalselectionactinguponvariationwithinapopulation.Organismswithfavoredtraitswithinagivensetofenvironmentalcircumstanceshaveaselectiveadvantageoverindividualswithdifferenttraits.Itisthismechanismthatleadstospeciation.Itisimportanttounderstandthatfavoredtraitsareonlyadvantageouswithinaparticularsituationandmaynotaidsurvivalinanothercircumstance.Acat’slongtailmayaidinbalancingonatreebranchbutbedisadvantageousinahousewithfrequentlyclosingdoors.InthecaseofthefictitiousClipbirds,differenttypesoffoodfavordifferentbeaksizes.Onebeaksizeissuperiortoanotheronlyincontext.Theclassicbirdbeakactivityusuallyinvolveshavingstudentsattempttopickupvariousobjectswithawidevarietyof“beaks,”includingscissors,spoons,etc.Thistraditionalapproachdemonstratescompetitioninanecologicalsense,butdoesnotclearlydemonstratevariationwithinapopulation,whichiscentraltoevolution.IntheClipbirdsactivitythe“beaks”areallthesame,exceptforsize.Theproportionofbig‐,medium‐,andsmall‐beakedbirdschangesinresponsetotheavailabletypesoffood.
Vocabulary:evolution,variation,population,adaptation,advantage,characteristic,speciation,reproductiveisolation
*CreatedbyAlJanulawandJudyScotchmoor.
See:http://www.ucmp.berkeley.edu/education/lessons/clipbirds/
LearningGoals
BigIdea7:Intra‐specificdifferences
• Individualsofthesamespeciesmaydiffer.
BigIdea8:Adaptation/Evolution
• Speciesareadaptedtotheirenvironmentsandspeciesadapttochangesintheirenvironment.Iftheenvironmentchangesonlycertainspeciessurvive.
• Organismswithtraitsbestsuitedtotheirenvironmenthavebetterchancesofsurvival.• Thoseorganismscarryingtraitsthatarebettersuitedforaparticularenvironmentwillhave
moreoffspring.• Selectionpressurecouldleadtoachangeinthecharacteristicsofapopulation.• Adaptationrequiresbothvariabilityandselectionpressure.• Givenanunderstandingoftheneedsofagivenorganism,identifyparticularphysicaltraitsthat
wouldhelpittosurviveinagivenenvironment–e.g.,“Whatwould<organism>needtohavetosurvivein<environment>?”
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BigIdea11:Descentwithmodification
• Speciesevolvefromcommonancestors.• Differentspeciescouldarisefromonespeciesifdifferentgroupshaddifferentselection
pressures.
LessonPlan
1.Estimatedtime
Thisactivityshouldtakeapproximately45minutes.
2.Introducetheactivity(Engage)
DisplaytheCliplandScenetransparencyandtelltheclassafancifulbutengagingstoryabouta
populationofimaginarybirds(Clipbirds)thatliveshappilyinafarawayfictionalplace,knownasClipland.Pointouttotheclassthatsomehowthelargepopulationbecamedividedintotwosmallerpopulations,eastandwest.Perhapsamountainrangeroseupinabighurry,oraflockoftheClipbirds
gotlostandendedupontheoppositesideofapreexistingrangeofmountains.(Thisisfictional,sohavesomefunwithit.)
3.Guidedinquiry(Explore)
Note:Initially,twogroupsofsixstudentswillstartthegame.Mostoftheclasswillbeinvolvedas“offspring”areadded.
Materials
• Sixbagsof“food”(assembledbyERteam,forEastandWestClipland,Seasons2‐4)• 20largebinderclips• 20medium‐sizedbinderclips• 20small‐sizedbinderclips• 30plasticcups• 1FoodValuestransparency(pdf)• 1ClipbirdPopulationstransparency(pdf)• 1CliplandScenetransparency(pdf)• 1overheadtransparencyprojector
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Procedure
1. AskthestudentstonoticehowthebirdsinEastandWestCliplandarealikeandhowtheyaredifferentfromeachother.Helpthemtonoticethatthebeaksofthebirdsvaryinsize:big,medium,andsmall.
Besuretodiscussthedifferentsizebeaksasvariationswithinapopulation.2. Explainthatbirdsofvariousbeaksizesusuallydojustfine,butittakesmorefoodenergyto
maintainthelargerbeaksizethanthesmallersizes.3. DisplaytheFoodValuesinMegacaloriestransparency.Allowstudentstimetounderstandthat
thevariousfoodshavedifferentfoodvaluesandthatbirdsofdifferentbeakssizeshavedifferentneeds.
4. Selectsixstudentstobeeastbirdsandsixtobewestbirds.Withineachgroup,givetwostudentslargeclips,twostudentsmediumclipsandtwostudentssmallclips.Eachstudent/birdalsogetsaplasticcuptoserveasitsstomach.Tellthemthatinordertoeat,theymustusetheclipsinthecorrectclipmode(demonstrate)andtheymustputallfoodthatissuccessfullyeatenintotheir“stomachs”(plasticcups).
5. Spreadoutthefoodforthe2ndSeasonintwoplacesthatrepresentEastandWestClipland.Note:itiseasiestonacarpetedfloor,sothefooditemsdonotrollaroundtoomuch.
6. Givethem20secondstoeatalltheycan.Makesuretheydonotscrapeorshovelthefoodintotheirstomachs,asthiswillbadlyskewtheresults.
7. Afterthefeedingfrenzy,putuptheFoodValuestransparency.Askstudentstocalculatethevalueofthefoodtheyate(helpthemwithoneormoreexampleswrittenontheboard).Ifastudentdoesn’teatenoughtosurvivethenheturnsinhisbeakandsitsdown.Ifastudentateenoughtosurvivethenshecontinuesaspartofthepopulation.Eachstudentwhoateenoughtoreproducegetsanotherbillthesamesizeasherownandselectsastudentfromtheaudiencetobeheroffspring.
8. HaveacrewofstudentscleanupalluneatenfoodfromthefloorandreturntotheZiplocbag.9. PutuptheClipbirdPopulationstransparency.Record2birdsineachoftheboxeslabeled1st
Seasonbecausethatwastheinitialnumber.Askthenow‐livingeastandwestbirdstoraisetheirbeaksiftheyarenowinthegame.Includeallsurvivingbirdsandtheiroffspring.Recordthenumbersinthe2ndseasonboxes.(Note:thesearethebirdsresultingfromthe2ndseasonoffeeding.)
10. Repeatdirections5‐9withthefoodforthe3rdseason.Beforespreadingthefood,letstudentsknowthatthecontentoffoodhaschanged(i.e.,thequantityofeachfoodtypeisdifferent).
11. Repeatdirections5‐9withthefoodforthe4thseason.Beforespreadingthefood,whichhasagainchanged,askstudentswhattypesofenvironmentalpressuresmighthavecausedthischange(e.g.,drought,insectinvasionruiningthecrop,etc.).
12. Haveallstudentsturnintheirbeaksandcleanupthemess.13. PutuptheClipbirdPopulationstransparency.14. AskstudentstodescribewhathappenedtotheClipbirdpopulationsandwhattheythinkcaused
thechanges.15. Keepthediscussiongoingsothatstudentscancreatetheirunderstandingthatselectioncan
happenwithinapopulationthatcanfavoronetypeoveranother.
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4.Discusstheactivity(Explain)
Theactivitycoversanumberofimportantconcepts:
• Evolutionresultsfromselectionactingupongeneticvariationwithinapopulation.• Adaptationsoftenpersistinapopulationbecausetheyareinsomewayadvantageous.• Inheritedcharacteristicsaffectthelikelihoodofanorganism’ssurvivalandreproduction.• Evolutionactsonwhatexists.• Theproportionofindividualswithadvantageouscharacteristicsmayincreaseduetotheir
increasedlikelihoodofsurvivingandreproducing.• Speciationrequiresreproductiveisolation.
Usetheaboveconceptsasaguidetoaskingquestionsorusethefollowingquestionsattheendoftheactivity:
• DisplaytheClipbirdPopulationstransparencyandaskstudentswhatthenumberstellthem.Whatdotheynoticeaboutthebirdsoneachside?
• WhathappenedtotheClipbirdpopulationsinthetwodifferentareas?• Whichtypeofbeakwashelpful(advantageous)inEastClipland?InWestClipland?Why?• WechangedfoodbydumpingoutthecontentsofaZiplocbag.Howwouldfoodsourceschange
forbirdsinreallife?Forexample,sometimeschangesintheweatheraffecttheamountofavailablefood.InFloridainthewinterof2009‐10,therewasacoldsnapandorangetreeswereaffected.
5.Makeanevolutionarytree(Elaborate)Aftertheactivity,displaythefoodbagsinorder–WestClipland,Seasons2,3,and4ononeside;EastClipland,Seasons2,3,and4ontheother.Askstudentsaboutthecontentofthesebags.Whathappenedtothefoodsupply?Cantheycomeupwithscenariosforwhythismighthavehappened?Howdoesthistreeofbagsrelatetothe"treeoflife"intheLegoactivity?