Download Predation Similar to both herbivory and parasitism Interaction with

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.