17.0147.014Lectures 33,34,35Lectures 33,34,35Species InteractionsSpecies InteractionsMay 5, 7, 10 2004May 5, 7, 10 2004Types of CompetitionConsumptive competitionPreemptive competitionOvergrowth competitionChemical competitionTerritorial competitionEncounter competition2The Fundamental Ecological Niche:“An n-dimensional hyper-volume every point on which a species cansurvive and reproduce indefinitely in the absence of other species”(Hutchinson)Food sizetemperaturehumidityThe Realized Ecological Niche:the niche actually occupied in the presence of other speciesFood sizetemperaturehumidityniche overlap leads to competition3One species eats seeds of one size rangeNumber consumedSeed size (one niche dimensionFigure 49.13aPartial niche overlap can lead toNiche Partitioning andCompetitive CoexistencePartial niche overlap: competition for seeds ofintermediate sizeSpecies 1Species 2Number consumedSeed sizeFigure 49.13b4Complete niche overlapSpecies 1: Strong competitorSpecies 2: Weak competitor,driven to extinctionNumber consumedSeed sizeFigure 49.13cStrong nice overlap can leadto Competitive ExclusionThe Spread of Introduced Zebra Mussels in theUnited States (1998 – 2001)Extensiveniche overlapcan lead tocompetitiveexclusion5Observed DistributionsChthamalusin upperintertidal zoneMean tidal levelBalanusin lowerintertidal zoneFigure 49.15aCOMPETITION EXPERIMENTUpperintertidalLower intertidal1. Transplant rockscontaining youngChthamalus tolower intertidal.2. Let Balanuscolonize the rocks.3. Remove Balanusfrom one-half ofeach rock.Monitor survivalof Chthamaluson both sides.On which side of the rocks doChthamalus survive better?ChthamalusBalanusFigure 49.15b6100806040200Young Chthamalus Older ChthamalusCompetitorabsentCompetitor presentCompetitorabsentCompetitor presentFigure 49.15cChthamalus survives better without competition.Percent mortalitySpring high tideNeap high tideMean tidal levelNeap low tideCould notbecome adultsdue tocompetitionLarvalSettlementZoneAdultDistributionRealizedNicheBarnaclessubject todesiccationSpring low tideLarvalSettlementZoneAdultDistributionDistribution of Two Barnacle Species – Balanus and ChthamalusBalanusChthamalusFundamental Niche7Galapagos FinchesANCESTOR FINCHBlue-back grassquitWarbler finchVegetarian finchSmall treefinchLarge tree finchMedium tree finchWoodpecker finchMangrovefinchLargegroundfinchMedium ground finchSharp-billedground finchLargecactus finchCactus finchInsect Eaters Bud EatersSeed EatersNiche Partitioningcan lead toAdaptiveRadiationHawaiianHoneycreepersAdaptive Radiation to Exploit a Variety of FoodSources Results in Speciation and a variety ofBeak Shapes8Stabilizing SelectionNumber ofIndividualswithphenotype0 10 20 30 40 50Medium-sized individuals favoredReducesVariation0 10 20 30 40 50Mean staysthe sameSelectionPeak gets higher and narrowerDirectional SelectionNumber ofIndividualswithphenotype0 10 20 30 40 50Mean ShiftsSelectionPeak shifts in one direction0 10 20 30 40 50Larger individuals favored9Number ofIndividualswithphenotype30 40 50Two populationsformingSelectionTwo PeaksDirectional Selection0 10 20 30 40 50Large and small individuals favoredAfrican Seedcracker(Pyrenestes ostrinus)Birds with smaller billscan consume softseeds more efficientlyBirds with largebills can crackhard seedsBirds withintermediate beaksize survivepoorlyWidth of lower bill (mm)Number of Birds10 2015100050Competition canlead tocharacterdisplacement10PredationPredationWhat drives the oscillation?Snowshoe Hare and Lynx Population Population CyclesLepus americausLynx canadensis1840 193011 years1870 1900Number of Pelts (thousands)15050100Hudson Bay Company Trapping Records(1840 –1940)HareLynx11Field Experiments - Lloyd Keith (1960’s to 1980’s)What accounts for population cycles?Food Supply or Predation?Control Phase of Hare PopulationRatio of Hare Density to ControlsFood Supply IncreasedPredators ExcludedFood Supply Increased &Predators Excluded1351351359111315CONCLUSION:Food Supply & Predation bothaffect population cycles.Source: Ricklefs, R. The Economy of Nature 3rd Ed., p.372Predatory mitepreyPrey mite12EvidenceEvidence forfor predationpredation asasanan evolutionaryevolutionary agentagent:- Cryptic Coloration- Physical and Chemical Defenses- Mimicry20151050ControltreesBrowsed andresprouted treesSalicortin concentration(mg/g dry mass)Figure 49.12bResprouted trees have more defense compounds.134003002001000Larvae fromcontrol treesLarvae frombrowsed andresprouted treesLarval survival time (sec)Figure 49.12cHerbivorous larvae have higher survivorship in the face oftheir own predators (ants) when they have been feeding onresprouted trees.Thus --- Leaf beetle larvae sequester anti-beaver compounds and use them as adefense against antsFigure 49.8bCorrelation between predation rate and prey defenseAttachment strength (N)Shell mass (g)Low predation High predation High predationLow predationSite type Site type14Figure 49.8cIs prey defense induced by presence of predator?Are mussel defenses inducedby the presence of crabs?Are mussel defenses induced by the presence of broken mussel shells?Seawater SeawaterCrab(fed fish, not mussels)Mussels MusselsMusselsMusselsNo crabBroken musselshellsIntact musselshellsShell thickness HIGH Shell thickness LOW Shell thickness HIGH Shell thickness LOWYes YesMutualismMutualism• Mutualism is a type of interaction that isbeneficial to both species involved.• It does not involve altruism. The benefits area by-product of each species’ own self-interest.• The costs and benefits of mutualism varywidely between partners, over time, and fromone area to the next.(Fig.
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