EcologyEcology

Lecture 10Lecture 10

Ralph KirbyRalph Kirby

PredationPredationPredators are agents of mortality and feed on living Predators are agents of mortality and feed on living organisms rather than scavengers or decomposersorganisms rather than scavengers or decomposersTypes of predationTypes of predation– CarnivoryCarnivory

Direct taking of animal prey for immediate consumptionDirect taking of animal prey for immediate consumption– Hawk taking a mouseHawk taking a mouse

– HerbivoryHerbivoryConsumption of plant material when plant is killedConsumption of plant material when plant is killed

– Consumption of nuts and seedsConsumption of nuts and seeds– ParisitoidismParisitoidism

Predator lives in or on a host and eventually kills to provide a food Predator lives in or on a host and eventually kills to provide a food sourcesource

– Parasitic waspsParasitic wasps– ParisitismParisitism

Predator lives in or on a host and consumes, but does not usually Predator lives in or on a host and consumes, but does not usually kill the hostkill the host

– Ticks on mammalsTicks on mammals– CannabilismCannabilism

Predation on same speciesPredation on same species– Tadpoles in a pondTadpoles in a pond

Similar formula to describe Similar formula to describe predation as for competitionpredation as for competition

Lotka and Volterra equation for predationLotka and Volterra equation for predation

PreyPrey– dNdNpreyprey/dt = rN/dt = rNpreyprey – CN – CNpredpredNNpreyprey

Where CNWhere CNpredpredNNpreyprey is mortality of prey due to predator. C is is mortality of prey due to predator. C is per capita capture rate and Nper capita capture rate and NpredpredNNpreyprey are the numbers of are the numbers of predators and prey respectively. predators and prey respectively.

PredatorPredator– dNdNpredpred/dt = B(CN/dt = B(CNpredpredNNpreyprey) - DN) - DNpredpred

Where B is efficiency of conversion of prey consumed Where B is efficiency of conversion of prey consumed (CN(CNpredpredNNpreyprey) and D is death rate of predators) and D is death rate of predators

Solving the equationsSolving the equationsFor predator densityFor predator density– NNpredpred = r/C = r/C

Growth rate of prey population is zero when density of Growth rate of prey population is zero when density of predators equals per capita growth rate of prey divided by predators equals per capita growth rate of prey divided by per capita capture rate of predators.per capita capture rate of predators.

Any increase in predator density will result in negative growth Any increase in predator density will result in negative growth in prey populationin prey population

For prey densityFor prey density– NNpreyprey = D/BC = D/BC

Growth rate of predator population is zero when rate of Growth rate of predator population is zero when rate of increase of predators is equal to rate of mortalityincrease of predators is equal to rate of mortality

Thus the two equations interact and this can be Thus the two equations interact and this can be done graphicallydone graphically

Result is 3Result is 3rdrd graph on left graph on leftThere is a cyclical rise and There is a cyclical rise and fall in both the predator and fall in both the predator and prey populations with timeprey populations with timeDensity of predators lags Density of predators lags behind density of preybehind density of preyFeast and Famine scenarioFeast and Famine scenarioPrey and predators are Prey and predators are never quite driven to never quite driven to extinctionextinctionMutual population Mutual population regulationregulationSimplified analysisSimplified analysis

ExcludesExcludes– Availability of refugesAvailability of refuges– Increased difficulty of Increased difficulty of

finding rare preyfinding rare prey– Multiple prey speciesMultiple prey species– Predator preference among Predator preference among

preyprey– CoevolutionCoevolution

Functional responseFunctional response– As prey increases, As prey increases,

predators take more preypredators take more prey– But howBut how

LinearLinear– Rate of predation is constantRate of predation is constant

Decreasing rate to maximumDecreasing rate to maximum– Rate of predation declineRate of predation decline

SigmoidalSigmoidal– Reaches maximum then Reaches maximum then

declinesdeclines

Linear Type 1Linear Type 1Mortality of prey simply density Mortality of prey simply density dependentdependent

No limits on systemNo limits on system

Decreasing Type 2Decreasing Type 2Predators can only each so much – Predators can only each so much – satiationsatiation

Time needed to kill and eat prey Time needed to kill and eat prey becomes limitingbecomes limiting

Sigmoid Type 3Sigmoid Type 3Capture rate is density dependentCapture rate is density dependent

Availability of coverAvailability of cover

Alternative prey when preferred is rareAlternative prey when preferred is rare

Prey not part of predators search Prey not part of predators search image, not a desirable food sourceimage, not a desirable food source

Prey switchingPrey switching– Palatable versus less Palatable versus less

palatablepalatable– Better return per killBetter return per kill– Less energy needed to find Less energy needed to find

and kill an abundant preyand kill an abundant prey

Numerical responseNumerical response– Predators reproduce morePredators reproduce more

However reproduction usually However reproduction usually slower than prey slower than prey

– Movement into high prey Movement into high prey density areasdensity areas

This aggressive response is This aggressive response is very important as it rapidly very important as it rapidly increases predator densityincreases predator density

This is an example of an aggressive This is an example of an aggressive responseresponse– Bay-breasted WarblerBay-breasted Warbler– Spruce budwormsSpruce budworms

Increased reproductive effortIncreased reproductive effort– Weasels as predatorsWeasels as predators– Rodents as preyRodents as prey– Predators followed prey in reproductionPredators followed prey in reproduction

CoevolutionCoevolution– Because of mutual interaction, there must be selection on both prey and predatorBecause of mutual interaction, there must be selection on both prey and predator

Prey are better at escapingPrey are better at escapingPredators that are better at capturingPredators that are better at capturingNote this is a moving target situationNote this is a moving target situation

– But there can be punctuationBut there can be punctuation

Prey defensesPrey defenses– ChemicalChemical

Pheromones to warn related species of attackPheromones to warn related species of attack– FishFish

PoisonsPoisons– Arthropods and fungiArthropods and fungi

– Cryptic colorationCryptic colorationHide in normal environmentHide in normal environment

– Moths on trees. MelanismMoths on trees. Melanism

– Flashing colorationFlashing colorationDistractionDistraction

– Deer and rabbitsDeer and rabbits

– Warning colorationWarning colorationLearnt behavior due to bad experienceLearnt behavior due to bad experience

– Bees and waspsBees and wasps

– MimicryMimicryCopy coloration of toxic speciesCopy coloration of toxic species

– Batesian mimicry of tropical butterfliesBatesian mimicry of tropical butterflies

– ArmorArmorDifficult to killDifficult to kill

– Clams, hedgehogsClams, hedgehogs

– BehavorialBehavorialGrouping togetherGrouping together

– More difficult to attach a large herd, see African antelopeMore difficult to attach a large herd, see African antelope– Timing of reproductionTiming of reproduction

Hunting tacticsHunting tactics– AmbushAmbush

Low success rateLow success rateLow energy consumptionLow energy consumptionCrocodiles, frogs, etcCrocodiles, frogs, etc

– StalkingStalkingLong search timeLong search timeShort pursuit timeShort pursuit timeCatsCats

– Extreme example is cheetahExtreme example is cheetah

– PursuitPursuitKnow where prey is present so there is a short search timeKnow where prey is present so there is a short search timeLong pursuit timeLong pursuit timeWolves, lions, hawksWolves, lions, hawks

– Note this is a simplificationNote this is a simplificationStalking can involve ambush at water holeStalking can involve ambush at water holePursuit can involve stalking if there is a large herdPursuit can involve stalking if there is a large herdCats can use ambushCats can use ambush

– Leopards up treesLeopards up trees

Each predator develops it own foraging Each predator develops it own foraging strategystrategy– Extreme example is cheetahExtreme example is cheetah

Very high speedVery high speedHigh energy consumptionHigh energy consumptionMust have high success rateMust have high success rateFailure has high priceFailure has high price

– RobinRobinDecides where to land and huntDecides where to land and huntSearch for food items such as a wormSearch for food items such as a wormOnce located, food item is attacked and capture Once located, food item is attacked and capture attemptedattemptedWhen to call off capture if unsuccessfulWhen to call off capture if unsuccessful

– Energy balanceEnergy balance– Success returnSuccess return– No success – look elsewhereNo success – look elsewhere

Thus predators show prey preferenceThus predators show prey preference– Optimum size for pry of wagtailOptimum size for pry of wagtail

Note also that predator may be prey to another Note also that predator may be prey to another speciesspeciesChoice of hunt area becomes importantChoice of hunt area becomes importantTheoretically there is an optimum strategy for Theoretically there is an optimum strategy for every predatorevery predator– But too many factor involved to identify this easilyBut too many factor involved to identify this easily

Note also that herbivory ideas put forwardNote also that herbivory ideas put forwardPlants defend themselvesPlants defend themselves– ChemicalChemical

QualitativeQualitative– PoisonsPoisons

FungiFungi

QuantitativeQuantitative– Tannins reduce protein availabilityTannins reduce protein availability

Bushes in desertsBushes in deserts

– StructuralStructuralThorns, spines, etcThorns, spines, etc

– Roses and AcaciaRoses and Acacia

Note also carnivorous plantsNote also carnivorous plants– Ambush strategyAmbush strategy– AttractantsAttractants

Complete Complete interaction interaction between plants, between plants, herbivores and herbivores and carnivorescarnivores

ParasitismParasitism– PredationPredation– Negative effectNegative effect– Do not usually kill hostDo not usually kill host– Eco- and Endo- parasitesEco- and Endo- parasites

Wide variety of access routesWide variety of access routes– MicroparasitesMicroparasites

Viruses, bacteria, fungi, protozoa etcViruses, bacteria, fungi, protozoa etcMay cause diseaseMay cause diseaseUsually direct transmissionUsually direct transmission

– Air, water, etcAir, water, etc– MacroparastitesMacroparastites

Liverflukes, ticks, mistletoe, etcLiverflukes, ticks, mistletoe, etcUsually more than one hostUsually more than one hostBoth direct and indirect transmissionBoth direct and indirect transmission

– Latter involves a vector such as a mosquito for malariaLatter involves a vector such as a mosquito for malaria

CommensalismCommensalism– ObligatoryObligatory– Minimization of negative effectsMinimization of negative effects

MutualismMutualism– Advantage to bothAdvantage to both

Life cycle can become complex as with meningeal worm and white Life cycle can become complex as with meningeal worm and white tailed deertailed deer– Definitive hostDefinitive host

Where adult stage reproducesWhere adult stage reproduces– Intermediate hostsIntermediate hosts

Where juvenile stages growWhere juvenile stages grow

Host response to Host response to parasiteparasite– AvoidanceAvoidance– GroomingGrooming– Inflammatory Inflammatory

response in animalsresponse in animals– Gall formation in Gall formation in

plantsplants– Immune response in Immune response in

animalsanimalsVaccinationVaccination

Parasite adaptationParasite adaptation– MalariaMalaria

Parasites affect host Parasites affect host survival and survival and reproductionreproduction– Malaria in humansMalaria in humans

Can end up with Can end up with balancebalance– Malaria in humansMalaria in humans

Sickle-cell anemia in Sickle-cell anemia in AfricansAfricans

Parasites can be major Parasites can be major regulators of populationregulators of population– HumansHumans

Black Death in14Black Death in14thth century centurySmallpox in 18Smallpox in 18thth century centuryCholera in 19Cholera in 19thth century centuryAIDS in 21AIDS in 21stst century? century?

– Buffalo, wildebeest and Buffalo, wildebeest and cattle in Africacattle in Africa

Rindepest in 19Rindepest in 19thth century century

Note importance of population densityNote importance of population density– Black Death in14Black Death in14thth century century

Needs lots of rats and some concentration of human populationNeeds lots of rats and some concentration of human populationNot a major problem to Romans or Chinese civilizations due to good urban Not a major problem to Romans or Chinese civilizations due to good urban planningplanning

– Smallpox in 18Smallpox in 18thth century centuryNeeds even high human population due to direct transmissionNeeds even high human population due to direct transmissionHalted by human evolutionHalted by human evolution

– VaccinationVaccination– Cholera in 19Cholera in 19thth century century

Needs even higher density and water/food transmittedNeeds even higher density and water/food transmittedHalted by human evolutionHalted by human evolution

– Clean water supply and bacteriologyClean water supply and bacteriology– AIDS in 21AIDS in 21stst century century

Needs even higher population densityNeeds even higher population density– Never a problem in low density central African origin except to some villagesNever a problem in low density central African origin except to some villages

Sexual transmission requires large number of contact, cf syphilis in 19Sexual transmission requires large number of contact, cf syphilis in 19 thth centurycenturyMajor effect on population once infection rate reaches 2%-5%Major effect on population once infection rate reaches 2%-5%

– Exponential growth in southern AfricaExponential growth in southern Africa– Affects human productivity directlyAffects human productivity directly

Halted byHalted by– Change in human behavior?Change in human behavior?– Science?Science?

Parasitism can evolve into mutualismParasitism can evolve into mutualism– Symbiotic or none symbioticSymbiotic or none symbiotic– At least one pair becomes totally dependent on the otherAt least one pair becomes totally dependent on the other– Ruminants stomach and microorganisms to digest plant materialRuminants stomach and microorganisms to digest plant material– RhizobiumRhizobium and nitrogen fixation in legumes and nitrogen fixation in legumes– FrankiaFrankia and nitrogen fixation in some woody plants and nitrogen fixation in some woody plants– Endomycorrhizae and plant rootsEndomycorrhizae and plant roots– LichensLichens– MitochondriaMitochondria– ChloroplastsChloroplasts

When things get so When things get so involved they cannot involved they cannot be separatedbe separated

2.5 billion year host 2.5 billion year host guestsguests

Mutalism can Mutalism can be none be none symbioticsymbiotic– PollinationPollination– Seed Seed

dispersaldispersal– Multiple Multiple

species may species may be involvedbe involved

Mutualism can involve Mutualism can involve multiple species and multiple species and affect the communityaffect the community– OaksOaks– TrufflesTruffles– VolesVoles– PigsPigs– HumansHumans

HumansHumans– Humans use trained pigs Humans use trained pigs

to find trufflesto find truffles– Human eat trufflesHuman eat truffles– Human keep oak forests Human keep oak forests

to harvest trufflesto harvest truffles– Voles spread truffle Voles spread truffle

sporesspores– Oaks need truffle Oaks need truffle

mycorrhizaemycorrhizae– Truffle farms in Australia Truffle farms in Australia

without voles need without voles need human innoculation of human innoculation of oaksoaks