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Short Film Some Animals Are More Equal than Others: Trophic Cascades and Keystone Species Student Materials NAME_______________________ DATE_________________ ThisquizwasdevelopedtosupplementtheviewingofthefilmSomeAnimalsAreMoreEqualthanOthers:Trophic CascadesandKeystoneSpecies. 1. True/False.Allmembersofafoodwebareequalinabundanceandintheirrelativeeffectsononeanother. 2. ExplainthereasoningorevidenceyouusedtoanswerQuestion1. 3. True/False.Everymemberofafoodwebisthepreyofanothermemberofthefoodweb. 4. ExplainthereasoningorevidenceyouusedtoanswerQuestion3. 5. WhichstatementbelowexplainswhythemusselsinMukkawBaywereabletoquicklycovertherockfaceinPaine’s experiment? A. Thestarfishtookupmostoftheroomontherocks,andwhenthestarfishwereremoved,themussels occupiedtheemptyspaces. B. Paineaddedmoremusselstotherocks,causingthestarfishtomovetootherhabitats. C. Thestarfishwerecompetingdirectlywiththemusselsforfood,andremovingthestarfishallowedthe musselsmoreaccesstothefood. D. Starfishfeedonmussels,sowhenthestarfishwereremovedthemusselsnolongerhadapredatorandtheir populationsgrewunchecked. 6. Inthefilm,Painerecallsthatayearafterthestarfishhadbeenremoved,thenumberofspeciesdecreasedfrom15to eight,afterthreeyearsthenumberwentdowntoseven,andafteranothersevenyearsitwasalmostallonlymussels. Inthecontrolplotsthenumberanddiversityofspecieswasbasicallyunchanged.Whichstatement(s)bestexplain(s) theseresults? I. Keystonespeciesarecriticaltothediversityandstabilityofanecosystem. II. Whenapredatorisremoved,thepreyofthatpredatoralwaysincreasesandspeciesnoteatenbythepredator alwaysdecrease. III. Thedisappearanceofproducersfromanecosystemcancausethenumberofpredatorstoincrease. A. Ionly B. IandIIonly C. IIandIIIonly D. I,II,andIII www.BioInteractive.org PublishedAugust2016 Page1of6 Short Film Some Animals Are More Equal than Others: Trophic Cascades and Keystone Species Student Materials 7. Beforethe1960s,mostecologiststhoughtthatthenumberofproducersinanecosystemwastheonlyvariablethat limitsthenumberofherbivores.Theideawasthateverylevelwasregulatedbytheamountoffoodfromthetrophic levelbelowit. a.Howdidthegreenworldhypothesisdifferfromthis“bottom-up”view? b.Imagineasimplefoodchain:Grass->Grasshoppers->Mice.Ifsnakesthateatmiceareaddedtothe ecosystem,howwouldyouredrawthefoodchaintorepresentthischange? c.Afterthesnakesareadded,wouldyouexpecttheamountofgrasstoincreaseordecrease?Explainyour reasoning. www.BioInteractive.org PublishedAugust2016 Page2of6 Short Film Some Animals Are More Equal than Others: Trophic Cascades and Keystone Species Student Materials Figure1.Since1972,Dr.JimEsteshadbeenstudyingafoodchainofkelp->urchins->seaotters,andthenintheearly 1990sorcasbeganeatingtheseaotters.ThedatacollectedbyDr.Estesareshown.PanelAshowsseaotterabundance aroundfourdifferentislandsfrom1972to1997.PanelBshowstheamountofseaurchins(seaurchinbiomass)in1987 and1997.PanelCshowstheamountofkelpthatseaurchinsateovera24-hourperiod(grazingintensity)in1991and 1997.PanelDshowsthenumberofkelpplantswithinaspecificarea(densityofkelp)in1987and1997.Thethicknessof thearrowsillustratesthestrengthoftheeffectonespecieshasonthespeciesbelowitinthefoodweb RefertoFigure1forquestions8through11below. www.BioInteractive.org PublishedAugust2016 Page3of6 Short Film Some Animals Are More Equal than Others: Trophic Cascades and Keystone Species Student Materials 8. In1997,whichspeciesistheapexpredatorinthefoodchain? A. Killerwhales B. Seaotters C. Seaurchins D. Kelp 9. WhichofthefollowingstatementsdescribesthedatainFigure1? A.Anincreaseinseaurchinbiomassisassociatedwithmoreintensegrazing. B.Anincreaseinseaurchinbiomassisassociatedwithgreaterkelpdensity. C.Predationofseaottersbykillerwhalesisassociatedwithgreaterkelpdensity. D.Seaotterabundancewasrelativelystablefrom1972to1997. 10. Completethefollowingsentence.Figure1illustratesthatwhenorcasstartedeatingseaotters,theseaotter population___________________,theurchinpopulation______________________,andthekelppopulation _____________________________. A. Decreased,decreased,decreased B. Decreased,increased,decreased C. Increased,decreased,increased D. Increased,increased,increased 11. ThearrowsontheleftandrightsidesofFigure1showtheeffectsofonespeciesonthespeciesthatareonlower trophiclevels.Thickerarrowsindicatealargeeffectandthinarrowsasmallereffect.Thearrowsontheleftshowa systeminwhichtherearealotofseaotters.Thearrowsontherightshowasysteminwhichtherearefewotters. Explainwhythedown-pointingarrowsontheleftsideofthefigurelookdifferentfromthearrowsontherightsideof thefigure. www.BioInteractive.org PublishedAugust2016 Page4of6 Short Film Some Animals Are More Equal than Others: Trophic Cascades and Keystone Species Student Materials Inthe1990s,ecologistsDeborahLetourneauandLeeDyerstudiedatropicalforestshrubcalledthepiperplantandthe variousspeciesofinsectsthatliveonandneartheshrub.Aspeciesofantusesthepiperplantasahomebyhollowingout someofitsbranchesandbuildingcoloniesinsidethehollowbranchcores.Theantsdonoteattheplant’sleaves.Instead, theleavesareconsumedmostlybycaterpillars.Whentheantsencountercaterpillarsorcaterpillareggsontheplant’s leaves,theyeithereatthemorkickthemoff.LetourneauandDyeraddedbeetlesthateatants.Figure2showstheresults ofoneofLetourneauandDyer’sexperimentsinwhichtheycomparedtheleafareaofpiperplantsincontrolplotstothat ofexperimentalplotstowhichtheyhadaddedbeetlesthateatants. MeanLeafAreaperPlantOver18Months 2500 2000 LeafAreaperPlant(cm2) 1500 1000 500 0 2 7 10 18 MonthsAfterStartofExperiment Withoutbeetle Withbeetle Figure2.Meanleafareapertree.Initialmeasurementsweretakenbefore(0to2months)andafter(7to18months) beetleswereaddedto40of80plants.Thelightgrayroundmarkersrepresentmeasurementstakenofthecontrolplots, towhichbeetleswerenotadded.Theblacksquaremarkersrepresentmeasurementstakenoftheexperimentalplots,to whichbeetleswereadded.Measurementsweremadeonallleavestocalculatethemeanleafareaperplant.Errorbars representstandarderrorofthemean. Refertothefiguretoanswerquestions12through17. 12. Forboththeplotswiththebeetlesaddedandthecontrolplots,statethemeantreeleafareaperplotthatthe scientistsrecordedafterrunningtheexperimentfor18months. www.BioInteractive.org PublishedAugust2016 Page5of6 Short Film Some Animals Are More Equal than Others: Trophic Cascades and Keystone Species Student Materials 13. Comparethetrendsinmeantreeleafareaperplotforboththeplotswiththebeetlesaddedandthecontrolplots overthe18monthsoftheexperiment. 14. Drawtwodiagramsthatshowthefoodchainsforboththeexperimentalandcontrolplots.Includeinteractions amongpredatorybeetles(ifpresent),ants,caterpillars,andpiperplants. Control Experimental 15. Describetheimpactofaddingthebeetlesoneachspeciesinthefoodchainabove. 16. WhichstatementdoLetourneauandDyer’sresultssupport? A. Addingbeetlesreducedantnumbersandtriggeredatrophiccascadethatincreasedthemeanleafarealeft onplants. B. Addingbeetleshadlittleeffectonthisecosystem,showingthatitisprimarilyregulatedfromthebottomup. C. Addingbeetlesreducedantnumbersandtriggeredatrophiccascadethatdecreasedthemeanleafarealeft onplants. D. Addingbeetlesreducedantnumbersandincreasedthecaterpillarpopulationsize,provingthatthe caterpillarsareakeystonespeciesinthishabitat. 17. DotheresultsoftheLetourneauandDyerexperimentsupportorrefutethegreenworldhypothesis?Explainyour answer. www.BioInteractive.org PublishedAugust2016 Page6of6