PopulationEcology–YellowstoneElkbyC.JohnGravesGroupNames: Hour Date:
DateAssignmentisdue:endofclass Score: +✓ - DayofWeek Date RockyMountainelk(Cervuselaphus)livinginYellowstoneNationalParkbelongtothemostabundantlarge-mammalpopulationinthepark.Theirhabitatincludeshigh-elevationgrasslandsandLodgepolepineforests.RockyMountainelkhavethechoiceoflivinginoneoftwoareasinYellowstone—theLamarValley(below)inthenortheasternregionoftheparkortheMadisonRiverValley(right).Inthisactivity,youwillbeaddressingtwokeyquestions:1.WhydoelkintheMadisonRiverValleyhaveashortenedlifespancomparedtoelkintheLamarValley
2.WhathascausedthereductionoftheMadisonRiverValleyherdsize?
Elkhabitatactivity1RockyMountainelkarethemostabundantlargemammalinYellowstoneNationalPark,numberingupto20,000inthesummer.Femaleelk,calledcows,usuallyhaveonebaby,orcalf,peryear.Maleelkarecalledbulls.Although widely distributed throughout Yellowstone, large
concentrations of elk are found in the Lamar Valley in the northeastregionofthepark.Thevalleyisapproximately14mileslongandupto2mileswidewithnotrees.TheLamarRivercutsachannelthroughglacialdepositmaterial.TheedgesofthevalleyriseuptoforestsofDouglasfir,Lodgepole pine, andEngelmann spruce. The predominant vegetation inthevalleyismountainbigsagebrushandseveralgrassspecies,includingIdahofescue.TheroadtoCookeCity,Montana,followsthenorthernedgeofthevalleyandismaintainedyear-round.In addition to elk, the area is home to wolves (reintroduced to
Yellowstone in 1995), grizzly bears, bison, coyotes, and other smallmammals.Snowfallisabundant,butforagingopportunitiesfortheanimalsexist,soawinterpopulationof8,000–12,000elkhashistoricallybeensupportedintheLamarValley.
Bycontrast, theMadisonRiverValley isonly6miles longandup to1milewide.TheMadisonRiverValley is formedbytheconfluenceof theFireholeandGibbonRivers at theheadof thedrainage.Theunderlyingbedrock is volcanic.TheWestEntranceroadcutsthroughthevalleyconnectingWestYellowstone,Montana,andMadison Junction,Wyoming, in Yellowstone Park. The road is closed towheeledtrafficinthewinter,butisusedbyover-snowvehicles.Aresidentherdof500–800elk has historically inhabited this area, along with mule deer, bison, coyotes,wolves, occasional grizzly bears, and other small mammals. Geothermal activityalong the valley floor keeps winter snow melted, away from the river and hotspringareas.Somegrassesareabletogrowyear-roundinthehotspringsarea,and
elkusethisfoodsourcethroughouttheyear.
1 Ifyouwereanelk,inwhichhabitatwouldyouchoosetoliveandwhy?
Figure1LamarValley
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2 Whatmajordifferencesdoyounoticebetweenthetwohabitats? 3 Whateffectdoyouthinkpredationhasontheelkherdsinthetwohabitats? Elkhabitatactivity2Inthemid1990s,researchersbegantonoticechangesinthepopulationnumbersofthetwoelkherds.TheaverageageofLamarValleyelkwasapproximately16years,withtheoldestanimalsliving20–25years.
IntheMadisonRiverValley,however,theaverageageofelkwasapproximately10years,withnoelklivingbeyond16years.
1 Whatareyourinitialreactionstotheagedifferenceinthetwohabitats?Listandexplainasmanycausesasyoucan. 2 Whatinvestigationswouldyouconducttodeterminethecauseofthedifferenceinlifespanbetweenelkintheirtwohabitats? Elkhabitatactivity3Inmid-January1995,14wolveswerereintroducedtoYellowstoneNationalParkinanattempttore-establishthepredatorinahistoricalecosystemafteritsremovalintheearly1900s.Pro-reintroductionadvocatesarguedthattheabsenceofwolveshadcreatedanartificialpredator–preyfoodchainandthatreintroductionwouldreturntheecosystemtoamorerealistichistoricalbalance.ThesewolveswerecapturedinCanadaandplacedinthree1-acreholdingpens.OneofthesepenswaslocatedneartheLamarValley.Thewolveswerereleasedintothewildafewmonthslater,andbegantoestablishterritoriesandpreyonlargemammals,especiallyelk,whichmakeup90%ofthewolves’winterdiet.Inwinter,awolfpackwillkillupto14elkpermonth.InJanuary2008,443wolveslivedin51packsintheGreaterYellowstoneecosystem.Outofthe51packs,11packs(171wolvestotal)livedwithinthebordersofYellowstoneNationalPark.
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1. WhatimpactdidreintroducingthewolveshaveonelkinYellowstoneNationalPark?
2. IsthisinformationadequatetoexplainthelifespandifferenceintheLamarValleyandMadisonRiverValleyelk?Explain:
3. Whatadditionalinformationisneededtoadequatelyexplainthedifferenceinlifespan? Elkhabitatactivity4Inthemid-1990s,researchersdiscoveredstarkdifferencesbetweenthejawsofLamarValleyelkandthejawsofMadisonRiverValleyelk(seeimagebelow).LamarValleyelkjawsshowedtypicalwearofteethatthetimeofdeath(Figure1A).MadisonRiverValleyelkjaws,however,showedacceleratedandmalformedwearpatternsofteethandabnormalitiesinjawdevelopment(Figure1B).Becauseoftheseabnormalities,manyMadisonRiverValleyelkdiedofstarvation.By2004–2005,researchersalsobegantoobserveadecreaseinthepopulationoftheMadisonRiverValleyelkherdsize.Thehistoricalnumbersofupto800elklivinginthevalleywerenowreducedto150–200.
1. Whatnewevidenceisgiveaboveandhowdoesitfactorintothedifferenceinaverageageofthetwoelkhabitats?
2. WhatdoyoubelievecouldbethecauseofacceleratedandmalformedwearofteethandjawsinMadisonRiverValleyelkherds?
3. Whatpossibleexplanationsarethereforthereducedpopulationsize?List&describeallthatcometomind.
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Elkhabitatactivity5ResearchersdiscoveredthatastheheavysnowsoftheMadisonRiverValleyaccumulatedovertheseason,elktendedtocongregateintherivervalley,especiallyaroundareasofhotspringactivity,toforageontheplantsthatgrowyear-roundin the geothermal areas. Plants gathered from these areas contained high concentrations of fluorine (F) and silicondioxide(SiO
2).
Silicondioxide iscreatedwhensilicon-richvolcanicrockdissolvesandcomesincontactwithgeothermalwater.As
the geothermalwater comes to the surface and cools, the dissolved silicon dioxide falls out of the solution, formingdeposits.Silicondioxideisfoundinstreamsandcanbedepositedontrees,boardwalks,andsoon.Itisalsofoundinthewaterabsorbedbytherootsofplantsthatliveinthehotspringareas.Itishard,likerock,andveryabrasive.Wheningestedbyelk, fluorineconcentrates inmineral tissuessuchasteethandbone.The jawsofelk living inthe
MadisonRiverValleycontainedmorethansixtimesthelevelsoffluorinefoundinthejawsofelkfromtheLamarValley.Theselevelsoffluorinebecometoxictothedevelopingteethandjawsofyoungelk,resultinginunevenorexcessivelyrapidteethwearandjawformation.Ofthe74jawsresearcherscollectedintheMadisonRiverValley,78%showedtheclassicsignsoffluoridepoisoning.
1 Whatnewevidenceisdescribedaboveandhowdoesitfactorintothedifferenceinaverageageofthetwoelkhabitats? 2 Doesthisnewinformationcauseyoutorejectanyearlyhypotheses?Explain. 3 Doesthisnewinformationadequatelyexplainthedecreaseinherdpopulation?Explain. 4 Arethereanynewhypothesestoexplainthedecreaseinherdsize?Create2-3newpossibleexplanations.
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Elkhabitatactivity6Wolvesprimarilypreyontheyoungandweakmembersofapopulation.BecausetheaverageageoftheMadisonRiverValleyelkherdhasbeenreducedduetothetoxiclevelsoffluorineandtheingestionofsilicondioxide,highernumbersofadultelkaresusceptibletopredationbywolvesduetothereducednumberofyoungerelk.Inaddition,thesnowpackon the slopes adjacent to the Madison River Valley is deep. Wolves have learned to force the elk away from thegeothermalareas intheriverdrainageand intothesurroundingslopeswheretheelkgetstuck inthedeepsnowandbecomeeasyprey.
1 Whatadditionalevidenceisgivenabove?HowdoesitfurtherexplainthereducedpopulationintheMadisonRiverValleyelkherd? 2 Asagroup,discussthecomplexitiesinvolvedinexplainingthedifferencesbetweentheelkintheLamarValleyandtheelkintheMadisonRiverValley. 3 Explainhowhabitatplaysaroleinthedifferencesbetweenthepopulationofthetwoelkherds.Using3examplesfromthisreading,showhowtheelkpopulationswereaffectedbydifferentaspectsofeachhabitat.1 2 3
