Download Student Materials Short Film Some Animals Are More Equal than

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