Textbook Notes (368,318)
Canada (161,798)
BIOB50H3 (47)
Chapter 11

BIOB50 - Chapter 11

6 Pages
92 Views
Unlock Document

Department
Biological Sciences
Course
BIOB50H3
Professor
Marc Cadotte
Semester
Winter

Description
Chapter 11: Competition COMPETITION IN PLANTS THATEATANIMALS:ACASESTUDY  CharlesDarwin(1875) providedclearexperimentalevidenceofcarnivorybyplants ­ Plants usea varietyofmechanisms toeatanimals o Venusflytraphasmodifiedleaves that looklikefangedjaws, yet attractinsectswithasweet smellingnectar o Other plantslackmovingparts, yet stillcaneatanimals. Pitcher plants, usenectar orvisual cuestolureinsectsintoapitcher- shapedtrap ­ Why dosomeplantseatanimals? o Competition o Carnivoryinplantsmay be an adaptationforlifeinnutrient-poorenvironments—perhaps providingawaytoavoidcompeting with other plantsfor soilnutrients. ­ Typically, therootsystems ofcarnivorous plants arelessextensivethanthose ofnoncarnivorousplantsthatliveinthesamearea INTRODUCTION  Tansleyconductedan experimentwithtwo speciesofbedstraw plants ­ The twospecies competedwith each other, andthatwhengrown onitsnative soiltype, each speciesdrovetheothertoextinction ­ Herestrictioninnature ofG. hercynicum andG. pumilum toaparticular soiltyperesultedfromcompetitionbetweenthesespecie  Tansley’sworkon bedstrawsisone ofthefirst experimentseverperformed oncompetition  Competition –aninteraction betweenindividualsoftwospeciesinwhich eachisharmed bytheirshared useofaresourcethat limitstheir abilityto grow, survive, orreproduce ­ Competitioncanalso occur between individualsofasinglespecies,inwhichcaseitisreferredtoasintraspecific competition ­ Asaresultofintraspecificcompetition, theresources availabletomembersofa high-densitypopulation canbereducedtosuchan extentthat growth, survival, orreproductiondecreasesoremigrationincreases ­ Intraspecificcompetitioncancause density-dependentreductionsinpopulationsize Concept 1.1CompetitionOccursBetweenIndividualsofTwo Speciesthat SharetheUse of aResourcethat LimitstheirGrowth, Survival, or Reproduction COMPETITION FORRESOURCES  Organismscompeteforresources, whicharefeatures oftheenvironmentthat arerequiredforgrowth,survival. Orreproductionandwhich canbe consumed orotherwise usedtothepointofdepletion ORGANISMSCOMPETE FORRESOURCES SUCH ASFOOD,WATER, LIGHTAND SPACE  Whenfoodisscarce, populationgrowthratesplummet  Food andwater areintuitiveexamplesofresourcesbecauseorganismsliterallyconsumethem  But anorganism does not needtoabsorb, eat, ordrinka substanceforittobearesource ­ Plants “consume:light  Spacecanalso beviewedasaresource ­ Althoughspaceisnot consumedin the senseofbeingeaten.Organismscanfillalltheavailablespace—thusdepletingit—andwhen theydo, populationgrowthratesdecrease  Physical Factors(abioticfactors) – featuresofthe environment thataffect populationgrowthrates butarenot consumed or depleted  The samesubstancecanbea physicalfactorforsomeorganismsandaresourceforothers ­ Ex. Terrestrialanimals, andaquatic animals oxygen COMPETINGORGANISMSREDUCETHEAVAILABILITY OFRESOURCES  Organismscanconsumeresourcestosuchanextentthatresourceavailability dropsandpopulation growthrates fall  When thetwospeciescompetedwitheachother, Synedra droveAsterionellatoextinction, apparentlybecauseitreducedsilica tosuchlow levels thatAsterionellacouldnot survive COMPETITION CAN INCREASE IN INTENSITY WHEN RESOURCES ARE SCARCE  Researchershave suggestedthat the relativeimportanceofaboveground andbelowground competition inplantsmightchange depending on whether aboveground or belowground resourcesare scarcer  S. scoparium individualsweregrown under threetreatments: 1. Withneighborsleftintact 2. with neighborrootsleftintactbutneighborshootstied back 3. withneighborroots and shoots bothremoved.  Intreatment 1therewasbothbelowground andabovegroundcompetition, whileintreatment 3therewas nocompetition.  Intreatment 2, thetied-backneighbor shoots didnot shade S. scoparium, but theact oftyingdidnot appeartoaffect neighborroots, sothat treatmentwasinterpretedasbelowground competition.  Abovegroundcompetitionwasestimatedasthe amountofcompetition intreatment 1minusthe amountintreatment 2.  Wilson and Tilman foundthatwhilethetotal competition(thesum of belowground and abovegroundcompetition) didnot differ betweenthelow- and high-nitrogenlow-nitrogen plots  They alsofoundthat abovegroundcompetitionforlightincreasedwhenlightlevelswerelow  Thus, theirworkdemonstratesthattheintensityofcompetitioncanincreasewhentheresourcebeingcompetedforisscarce. COMPETITION FOR RESOURCES IS COMMON IN NATURALCOMMUNITIES  Schoener, ConnellandGuravitchshowedthat competition had significant (thoughvariable) effectsona widerangeoforganisms, including carnivores, herbivores, andproducerssuchasplants Concept 11.2 Competition, Whether Direct orIndirect, CanLimitthe DistributionsandAbundancesof CompetingSpecies GENERALFEATURESOF COMPETITION  Sincethebeginningofecologyasa field of science, ecologistshavethoughtthat competition betweenspecieswasimportant innatural communities SPECIES MAY COMPETEDIRECTLY OFINDIRECTLY  ExploitationCompetition – Species oftencompeteindirectlythroughtheirmutualeffectsontheavailabilityofasharedresource  Interference Competition –occurswhenspeciescompete directlyfor access to aresourcethatbothrequire, suchasfood or space  Ininterferencecompetition, individualsperform antagonisticactionsthatdirectlyinterferewiththeability oftheircompetitorstouse alimiting resource  Interference competition alsooccursinplants  Thereisalso circumstantial evidencethatinterferencecompetitioncantaketheform of allelopathy, in whichindividualsofonespeciesrelease toxinsthat harmindividualsofother species COMPETITION ISOFTENASYMMETRICAL  Becausecompetitionreducestheresourcesavailableforthegrowth,survival, andreproductionof bothspecies, eachspecies isharmedtosome extent  Inmanycases, however, theeffects ofcompetitionareunequal, or asymmetrical:onespeciesisharmedmorethantheother. Thisasymmetryis especiallyclear insituations in whichonecompetitor drivestheother to extinction  The effectofthesuperiorcompetitorwouldbemuch greater thanthe effectoftheinferior competitor COMPETITION CANOCCUR BETWEEN CLOSELYORDISTANTLY RELATED SPECIES  BrownandDavidson: ­ Lasted3yearsand usedfourtreatments:  Plotsinwhicha¼ -inchwiremesh fenceexcludedseed eatingrodentsandfrom whichrodentswithinthefencewere removedbytrapping  plotsinwhichseed-eatingantswere excludedby applying insecticides  plotsinwhichboth rodents and antswereexcludedbyfencing, trapping, andinsecticides  plotsinwhichbothrodents and antswereleftundisturbed(control plots) ­ The resultsindicatedthat rodentsand antscompeteforfood ­ These results suggestedthat wheneither rodents orantswereremoved, thegroupthat remainedateroughlyasmany seedsasrodents and antscombinedateinthecontrol plots ­ Thus, under natural conditions, each groupwouldbeexpectedtoeatfewer seedsinthe presenceoftheother groupthanitcouldeat whenalone ­ Overall, irrespective ofwhetherthey arecloselyordistantlyrelated,organisms cancompeteiftheysharetheuseofaresourcewhose supplyislimited COMPETITION CANDETERMINE THEDISTRIBUTIONSOF SPECIES  In somecases, competitionalsoaffectedwherethespecieslived  Competitionmayrestrict speciesto certainportions ofa particular habitat, oritmay determinethe broad geographicregionsinwhichspeciesare found(orboth)  Local Effects ­ JosephConnell(1961a,b)examined factorsthatinfluencedthe distribution, survival, andreproductionoftwobarnacle species, ChthamalusstellatusandSemibalanus balanoides ­ The larvae of bothspecieswerefound throughout the upper andmiddleintertidal zones. ­ However, adultChthamalus usually werefound onlynear thetopoftheintertidal zone, whereas adultSemibalanus werenot found there, butwerefoundthroughoutthe restthesedifferencesindistribution?  To test theimportanceofcompetition, hechosesomeindividualyoung barnaclesofeach speciesthathad settledineach zone andremovedallnearbymembersofthe other species  For other focalindividuals, heleftnearbymembersoftheother speciesinplace. Hefoundthat competitionwith Semibalanus excludedChthamalus from allbutthetopoftheintertidal zone.  Astheygrew, Semibalanussmothered(bygrowingontopof), removed(by growingunderneath, hence pryingoffthe rocks), andcrushedthe Chthamalus  Averaging across allregions ofthe intertidal zone, only 14%of Chthamalussurvivedtheirfirst yearwhenfacedwith competitionfrom Semibalanus, whereas 72%survivedwhere Connellhadremoved Semibalanus  Chthamalusthat surviveda year of competitionwith Semibalanusweresmall andreproducedpoorly  Semibalanus, in contrast, wasnotaffectedstronglybycompetitionwith Chthamalus.However, whether Chthamalus was removedornot, Semibalanusdried out andsurvivedpoorly nearthetopoftheintertidalzone  Thus, Semibalanusappearsto h
More Less

Related notes for BIOB50H3

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit