17.0147.014Lecture 33Lecture 33May 9May 9Species Interactions Species Interactions ––CompetitionCompetition20072007Consumptive competition occurs when organisms compete for the same resources.These trees are competing for nitrogen and other nutrients.Figure 49.14 upper leftPreemptive competition occurs when individuals occupy space and prevent accessto resources by other individuals. The space preempted by these barnacles isunavailable to competitors.Figure 49.14 upper rightOvergrowth competition occurs when an organism grows over another, blockingaccess to resources. This large fern has overgrown other individuals and isshading them.Figure 49.14 middle left2Chemical competition occurs when one species produces toxins that negativelyaffect another. Note how few plants are growing under these Salvia shrubs.Figure 49.14 middle rightTerritorial competition occurs when mobile organisms protect a feeding orbreeding territory. These red-winged blackbirds are displaying to each otherat a territorial boundary.Figure 49.14 lower leftEncounter competition occurs when organisms interfere directly with each other’saccess to specific resources. Here, spotted hyenas and vultures fight over a kill.Figure 49.14 lower leftThe 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 sizetemperaturehumidity3Food sizetemperaturehumidityniche overlap leads to competitionThe Realized Ecological Niche:the niche actually occupied in the presence of other speciesFood sizetemperaturehumidityOne 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 niche overlap can leadto Competitive ExclusionThe Spread of Introduced Zebra Mussels in theUnited States (1998 – 2001)Extensiveniche overlapcan lead tocompetitiveexclusionConnell’s BarnaclesA classic ecological experimentdemonstrating nichepartitioningPelagic larvaeare sessile asadultsObserved Distributions: Is this due to competition?Or differential tolerance of desiccation?Do an Experiment!Chthamalusin upperintertidal zoneMean tidal levelBalanusin lowerintertidal zoneFigure 49.15a5COMPETITION 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 49.15b100806040200Young Chthamalus Older ChthamalusCompetitorabsentCompetitor presentCompetitorabsentCompetitor presentFigure 49.15cChthamalus survives better without competition.Percent mortalityConnell’s BarnaclesPelagic larvaeare sessile asadultsBalanus outcompetes Chthamalusbut is more vulnerable to desiccationChthamalus is resistant todesiccation but is outcompetedby BalanusSpring high tideNeap high tideMean tidal levelNeap low tideCould notbecome adultsdue tocompetitionLarvalSettlementZoneAdultDistributionRealizedNicheBarnaclessubject todesiccationSpring low tideLarvalSettlementZoneAdultDistributionDistribution of Two Barnacle Species – Balanus and ChthamalusBalanusChthamalusFundamental Niche54.17Purves6Stabilizing 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 favoredNumber 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 tocharacterdisplacement7Galapagos FinchesANCESTOR FINCHBlue-back grassquitWarbler finchVegetarian finchSmall treefinchLarge tree finchMedium tree finchWoodpecker finchMangrovefinchLargegroundfinchMedium ground finchSharp-billedground finchLargecactusfinchCactus finchInsect Eaters Bud EatersSeed EatersNiche Partitioningcan lead toAdaptiveRadiationHawaiianHoneycreepersAdaptive Radiation to Exploit a Variety of FoodSources Results in Speciation and a variety ofBeak
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