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Lecture 9

ecology lecture 9-13

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Biological Sciences
Marc Cadotte

Lecture 9-10 :  A.J Tansley1 expt in competition(1917)2 species of bedstrawG.hercynicum(acidic soils) + G.pumulium(calcareous soils)  Both grown individuallysurvive on both soils, togetherdetermined by soil type on which it is grown  Darwin theory ofstrrugle of existencecompetition limits abundance/distribution of competing species  Inter-specific Competition—>b/w 2 diff species, both harmed as using same resource  Intra-Specific(think Intra-Murals)-competition b/w individuals of same species  Outcome of competitionlimits growth, survival & reproduction of each (competing species)  Resourcesmust be depleted(ie :Food/Water/ Space etc)eg: space limiting resource for corals  TILMAN EXPT19812 species of diatoms(single cell algea, make cell walls of SiO(2)  Grow Alonereached carrying capacity, deplete resource(SiO2)  Grow Together1 drives other to extinction  Syndera(Fig 11.4, blue line)wins competition against other  ReasonEven @Lower conc of resourcespecies can persist(survive Hardship)R*  Schoener(1983)interspecific competitionsstudy 390 speciesmajority show effect of comp in some conditions(76%) and all(57%)  Connel(1983)50% of 215 species found competition important  Hencecompetition important in enviro  Gurevitch(1992)comp had significant effect on species(competitive effects for 93 species)  Exploitation Competitioncompete indirectlyuse of same resource(R-star)eg : Diatoms in the Tilman Expt  Interference CompetitionCompete directlymay fight etc(acorn barnacles)/ Voles excluding voles from preffered competition  Allelopathy(interference comp)individuals release toxins that harm others(plants)  Egcattle avoid spotted knapweed(+ve advantage), plants relase catechin(into soils)reduce germination/growth of native grass  Comp strongest b/w related/similar species  Distant speicesBrown & Davvidson expt(1977)rodents vs ants  Conditions1) Wire meshexclude rodents 2)Insecticides>exclude ants 3)Exclude both 4)Control  Resultw/o rodentsants inc 71%, inc biomass / nos in case of rodents(w/o ants)  In presence of competitionboth species eat less than normal  Connel(1961)examine factors affecting distribution, survival, reproduction of 2 barnacle species  Larva of both overlapped on middle intertidal + upper zones  AdultsCthalamus(top of intertidal zone),Semibalanus(rest of intertidal zone)  Competitionaffects Geographical Distribution  EgNatural Expt on chipmunk species in Southwestern U.S  Patterson(1980,81)living alone occupy broader elevations/habitats(not in presence of predators)  Competitionmay lead to co-existence  Gauss expt(1930)3 species of Parameciumgrow alonereach carrying capacitygrow togetherdrive other to extinction  Co-existence @ lower sizes of poppossibly due to diff resources being used  Competitive EXCLUSION Principle2 species using limiting resource cannot CO- EXIST if used in same way  Similar Ecological niche(with competitior)leads to extinction  Grinnel(1917)defined NICHE(no 2 species occupy same niche)  California (1925)hungarian patridge(competitior) vs California Quaildue to same nichecan go extinct  Diff elevations usednot Extinct, contrary to what was expected  Resource Partiioninguse Limited Resource in diff ways  EG; Schoner(1974)lizard use space in diff ways-less competition  Cyanobacterium competitionboth green/red bac co-exist in white light  Red lightgreen bac excel(red bac reflects) and green light(red excels)  Character Displacement(CD)Due to Natural Selectionchange in morphology of competing species  Eg; Darwin Finchesliving togetherdiff beak sizes(even if diff from optimal size)  W/O Competitionbeak size is intermediate value10mm, changes due to competition  CD examplesdiff morphology of sticklebacks living in same lake  Outcomediff morphology from competitior  less competitiongrow faster  Measured log of growth vs Morphological Index(similiarty of species)--ve correlation-ve index = higher growth  Competition Reversal  due to environmental conditions, species interactions , disturbance  Outcomepredator/prey roles reverse  Eg : Presence of herbivores in (ragwort flea beetles/ ragwort)  Ragwort flea beetles dec ragwort popcompetitior size increases  No Flea beetleragwort-superior competitior  CompetitionEvolutionary Change-alter outcome of competition  Expt : House-Fly vs Blow-Fliesgrow in chambers + same food  Houseflysuperior initially  Over timesituation change houseflies extinct  Conclusion-possibly some evolutionary change  LOTKA-VOLTERRA EQUATIONS : Competitive Exclusion  dN1/dt = r1N1(1- (N1+αN2)/K1  dN2/dt = r2N2(1-(N2 + βN1)/K2 nd  Basciallylogistic for 1 species + abundance of 2  Α,β Competition co-efficientseffect of 1 species on another(constant) effect of 2 on 1 (alpha) and vice-versaExtent to which resources by 2 decreases per capita growth of 1  α=1 = effect of species on each other  α<1species 2 weaker competitor  α>1-species 2strong competitior  Theory of Modelcompete for similar reosurcesCompetitive Exclusion  Related casesN1 = 0,N2 = 0, dn/dt0(no change in pop density)  Straight line relationshipsrefer to 0 population growth isoclinestells under which conditions species inc/dec  Isoclines do not crosscompetitive Exclusion  Co-Existence Equationαr/aprey population dec >P < r/apop inc(think that inc P makes the Prey Equation more –ve)  dP/dt = 0N = m/baN> m/ba(inc pop)N< m/ba(dec pop of Predators)  0 population isoclinesPrey/Predator pop cycles  Prey cycle 1 step aheadEg : inc prey popinc predator popdec prey popdec Predator pop (think Physics Wavesone cycle behind..lag by about 45 degrees)  -ve of ModelAmplitude of cycle depends on initial nos of Prey/Predators  Large Ampdrives species to extinction  Extinction realistically rare by predation-because-1)Habitat Complexity 2)Spatial Refuges 3)Prey Switching 4)Prey Respond to Predation 5)Evolution  Pop cycleshard to achieve in labs Huffaker’s expt(1958)predatory mite eats herbivorous 6-spotted miteboth went extinct(prey easy to find)  Hairston Exxptrotifer(predator)Algal (prey)Aschynchrous cycling of population  Predator peakprey low and vice-versa  SynchronousInc / Dec at same timestheoretically Expected  Reasons for asynchronous1)Algea evolve (to face predation) 2)Accumulation of toxins(alter algeal physiology) 3)Algal Nutritional Quality inc with Nitrogen Concentrations 4)Rotifer Egg Viability inc with Prey Density  Yoshide(2003)test hypothesisOnly mathematical model including evolution in prey was right in prey-predator model(proved hypothesis 4)  Outocome single genotype algea(no evolution)synchronous cycles  Multiple GenotypesAsynchronous cycles  Algeal Genotypes Ω Poor competitiors in their community(trade-off)  High Predator popΩ genotype(algea) inc, predators dec  Low Predator Ω genotype(algea) outcompetedreplaced by other genotypespredator inc  Lynx / Snowshoe Hare Cyclessynchronous pop cycles  @High Density of hareLow reproductive Rate  Possible Reasons1) High Hare densityFood limited (although some are declining even with food)  2)Predation by lynx + other predators  Questions1)Hare birth rate drop during decline phase of cycle  2) Nos rebound slowly when predators low  3)Low hare nosphyscial conditions of hares worsen  Krebs Expt1*1 km strips 4 plots1) control 2) + Food 3)- predator 4) + food/- predator Survival Rates/densities of hares monitored for 8 years  Highest in + food/ - predator  Mathemtatical Model support field Expt(King and Schaffer 2001)  Lynx Movement from Low to High prey abundance=>Geographic Synchrony (hare cycles)  + Food/- Predators cyclefences did not remove other predators like birds of prey  Stress caused by fear of predator attack  Decling condition in D
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