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Predation Similartobothherbivoryandparasitism Interactionwithverystrongfitnessconsequences,especiallyfortheprey Thus,lotsofstrongselectiveforcesandextremeadaptations Therecanbe3responsesinthepreypopulation: (graph:Prey#vstime) 1. Noeffect:ifthepreysuccessfullyevade,ortheyreproducequicklyenough thatthepredatorskeepthematcarryingcapacity. 2. Extinction:Preycan’tescape,theyallgeteaten.Predatorsmayfollow,ifno otherfood. 3. Cycling(we’lltalkmoreaboutthat) Famousexample:haresandlynxes Thedatasetisverygood—collectedbytrapperssincethe1850’s Observed:bothpopulationscycleevery10years,thelynxesbehindthehares(ppt) Whatwouldcausethat?(studentideas) Earlyhypothesis:sunspotsaffectedthevegetation,whichaffectedthehares.A charmingidea,butthetimingneverlinedup. Overpopulation:thehareswouldincreasetheirpopulationrapidly,andthen disease,parasitism,andfoodshortageswouldstarttodrivetheirnumbersdown. Predation:thelynxeswouldincreaseuntiltheywerekillingmoreharesthanwere born,thenwoulddecreaseinturn. Thehares: Foodsupply:theyliveinborealforests,eatunderstoryplants(roses,willows),buds andtwigs.Theyeatalotofbiomass. Foodshortageshavebeendemonstratedinwinters,wheretheyjustrunoutoffood. Foodqualityalsodiminishes:feedinginducesdefenses(secondarycompounds)for upto2years.Terpenesandphenolics. Predators: Manyspeciespreyonthem:lynx(specializeonhares),coyotes,owls,goshawks, foxes,weasels. Moreofthesemayalsocycle,wejustdon’thavethelongtermdatatosee. Athighdensities,predatorshavebeenshowntocause60-90%ofthehare mortalities. Activity:Drawthecycle,havestudentstapeuptheeventsatthepointwherethey’re true. Testingsomeofthesehypotheses: Areallyimpressivefieldexperiment 9blocks:1kmeach Treatments: Control Supplementaryfoodforthehares Fertilizer:notdirectsupplementalfood,butimproveplantquality Excludemammalianpredators Excludepredatorsandalsosupplementalfood Ranthisfor8years(!),trackedtheharepopulations Inallblocks,sawtheharepopulationincreaseandthendecrease Butthenumbersdependedonthetreatment: Supplementaryfood:3xtheharepopulation Nopredators:2xthecontrolpopulation Both:11xthecontrolpopulation Conclusion:Bothpredatorsandfoodsupplyreducetheharepopulationinthecycle ThesecycleswereformalizedbyLotkaandVolterra Nh=populationsizeofprey Np=populationsizeofpredators rh=birthrateofprey p=rateofpredation c=conversionfactor—aconstantrateatwhichpreyareconvertedintoprey dp=deathratesofpredator dNh/dt=rh*Nh–pNhNp Thechangeinthepreypopulationdependsontheexponentialpopulationgrowth minusthedeathscausedbypredators dNp/dt=cpNhNp–dpNp Changeinpredatorpopulationdependsontherateatwhichtheydestroypreyand turnthemintooffspring,minusthepredatordeaths Ifyouchartthis,yougettheclassiccycle,withpredatorsfollowingaboutaquarter cycleaftertheprey.Stableoscillations. Experimentalevidence: PeoplehavetriedtorecreateLVcyclesinthelab Inmostcases,thepredatorsjustdrivethepreytoextinction(secondresponsefrom beginning) Inordertosurvive,thepreyneeda“refuge” Activity:handoutexamplesofrefuges,havestudentsworkingroupstocomeup withclassificationoftypesofrefuges,discussasaclass Approximateclassifications:hiding,speed,unpalatability,saturation,size,crypsis Crypsis—colorationthatmakesyouhardtosee(generallybymatchingthe substrate) Famouscrypsisstory:Pepperedmoths InEngland,before1811,allcollectedmothswerelightgrey Bythe1850’s,insomeplaces,almostalldarkgrey/black Causedbypollution—causedthetreesinsomeforeststobedarkened Aftercleanairactswerepassed,thelightmorphsincreasedinfrequencyagain Hypothesis:Evadingpredationbybirdsexertedselectiononthecoloration Experiments:severalovertime(somequiterecently) Pinneddeadmothstotrees,countedthenumberofstrikes.Contrastingmothswere moreattacked. Release-recaptureexperiments:Thecontrastingmothhadlowersurvival Recent,similarexperimentshavevalidatedtheseresults. Theselectivedifferentialwas0.1-0.2:meaning,lightmothsinlightforests (nodarkonesleft)hada10-20%fitnessincreaseoverdarkmoths—strong selection Geneticsofmelanisminmoths Hadpreviouslytestedcandidategenes—noneofthemwereit Linkagemappingletthemidentifyaregion Justthisyear,astudyidentifiedthegeneandmutation carbonariaisthegene;itaffectsexpressionofcortex,whichisimportantin patterninginHeliconious Insertionofalargetandemly-repeatedtransposableelementintothefirst intronofthegenecausedthechange Itwasasinglemutation,justoneorigin,whichoriginated~1815 Strongsignaturesofselectionaroundthegene Anotherclassicsystemforcrypsis:mice(Hoekstralab) Pigmentationinmammalsiscontrolledbytwomainpigments: 1. Eumelanin(black-brown) 2. Pheomelanin(red-yellow) Thepathwayiswellcharacterized,whichhasbeenamajoradvantageforstudies. 2genesthatareoftenimportant(inmammalsandotherspecies): Mc1R:signalsforhighlevelsofamoleculecAMP,whichtriggersproduction ofeumelanin Agouti:agonistofMC1R:bindstoitandinhibitsit,whichleadstoareduction incAMP,andtheproductionofpheomelanin Mice:selectiontomatchsubstratestudiedsincethe1920’s. NewMexico:blacklavaflowsandwhitesanddunes:morphsmatch Florida:lightonbeaches,darkinland Multipletraitsareinvolved: Color(whichpigment,howmuch) Thedorsal-ventralboundary Tailstripewidth Facialstripes Examplesofconvergece:blackonalllavaflows,evenifthere’snomigration betweenthem(independentevolution;incontrasttothemoths) Becausetheyhavestrongcandidategenestostartwith,theycandoreallygood, detailedwork(someofwhichwewillbereading) Ongoingdebateinevolution:relativeimportanceofcodingmutationsvs.regulatory mutations Pigmentationhasbeenreallyinterestinghere Mc1R:oneoftheonlygeneswherealmostallknownmutantsarecodingchanges Agouti:generally,regulatorychanges Examplesofboth: OldfieldmiceinFlorida Betweenenvironments,seedifferencesinbothMc1R(lighteroverallcolorcaused byacodingmutation)andAgouti(changesincolorpatterncausedbyaregulatory change) Alsoepistasisgoingon—thevariationinMc1Risonlyvisibleinthevariant Agoutibackground Anotherquestion:howtoactuallymeasureselectiondirectlyonanimals? Anongoingquestion:here,theyuseplasticinemodels Actuallymeasuringselectiononaspecificmutationisabigdeal,theyweresomeof thefirsttodoit.