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GeneralEcology(BIO160) Worksheet#16 Dept.ofBiologicalSciences SacramentoState Worksheet16:Mutualism 1. Whatisthedifferencebetweenasymbioticandanon-symbioticmutualism?Giveanexampleof each.Asymbioticmutualismisoneinwhichtwodifferentspeciesareorganicallylivingtogether.This contrastswithanon-symbioticmutualisminwhichthetwopartnersliveseparateexistences.Examplesof symbioticmutualismsare:plantsandmycorrhizalfungi,plantsandRhizobiumbacteria,coralpolypsand zooxanthellae,andlichens(afungusandalgaorcyanobacterium.Examplesofnon-symbioticmutualismsare: plantsandpollinators,plantsandseeddispersers,ant-plantmutualisms,seaanemonesandanemonefish,etc. 2. Reef-formingcoralsareanexampleofa____symbiotic_____mutualism.Whatdoeseachpartnerin thecoralpolyp-zooxanthellaemutualismgetoutoftherelationship?Thecoralpolyp-zooxanthellae mutualismisoneinwhichthecoralpolypreceivescarbonprovidedbythezooxanthellaefromphotosynthesis andinreturnthezooxanthellaereceivenutrientsandshelterfromthecoralpolyp. 3. Mutualismsfallintothreecategories:dispersive,defensive,andtrophic.Foreach,describethe natureofthemutualismandgiveanexample. DispersiveAdispersivemutualismiswhenonespeciesinthepartnershipdispersesthepropagules(e.g., seeds,pollen,etc.)oftheotherandinreturnbenefitsbyeitherconsumingthepropaguleasafoodsourceor usingthehostasaplacetolayeggs.Anexampleisscrubjays(birds)thatgatheracornsandburytheminthe groundandawayfromthetreetoeatlater;althoughsomeacornsarelaterfoundandeatenbythebirds, manyarenotandgerminateintheburiedlocation.Anotherexampleisinsectpollinators,whichcollectpollen forfoodfrommultipleflowersandindoingsospreadthepollenfromoneflowertoanother. DefensiveAdefensivemutualismiswhenonespeciesinthepartnershipdefendstheotherandinreturn benefitsbybeingprovidedwithfoodand/orshelterbythehost.Anexampleofthisisant-plantmutualisms; inthismutualismantsvigorouslydefendtheirplanthost,whichinreturnprovidestheantswithfood(inthe formofproteininBeltianbodiesandsugarsinextra-floralnectaries)andinmanycasesalsoshelter. TrophicAtrophicmutualismiswheneachspeciesinthepartnershipprovidestheotherwithnutrients.An exampleisthecoralpolyp-zooxanthellaemutualisminwhichthecoralpolypprovidesprotection/shelter, nutrients,andCO2forthephotosyntheticzooxanthellae(dinoflagellatealga)andthecoralpolypreceives carbohydratesprovidedbythezooxanthellaefromphotosynthesis. 4. Mycorrhizalfungiplayanimportantroleforplants.Describetheroleofmycorrhizalfungiforplants andwhateachpartnergetsoutoftherelationship.Compareandcontrasttheplant-mycorrhizal mutualismfromtheplant-Rhizobiummutualism.Plantsandmycorrhizalfungiareasymbioticmutualism inwhichafungalpartnerreceivescarbonprovidedbytheplantfromphotosynthesisandtheplantreceives nutrients(andoftenwater)fromthefungus.Theplant-Rhizobiummutualismisalsoasymbioticmutualism, butRhizobiumarebacteriathatfixnitrogen(N2gas)fromtheatmosphere. 5. Chooseadispersivemutualism.Describethebenefitstobothpartnersandexplainhowitcouldhave evolved.Example:Seeddispersalbyants(calledmyrmecochory).Myrmecochorousplantsbenefitbecause antscarryseedstotheirnests,wheretheseedsareshelteredfrompredationbyseed-eatingrodentsandhave accesstoincreasednutrientsinthenest.Antsbenefitbecausetheseedsprovidethemwithessential nutrientsattractivetotheants.Thenutrientsareprovidedinaneliaosome–anappendageofnutritional tissueattachedtotheseedcoat. Duetonaturalvariationinseedcoatchemistry,someseedsmayhavecontainedincreasedessentialnutrients neededbytheantsthattheantscoulddetectfromchemicalcues.Antsselectivelysoughtthoseseedsout andbroughtthosetotheirnutrientrichnests.Seedsthatwerebroughttoantneststendedtosurviveand reproducemorethanthoseseedsthatdidn’tgettakentoantnests.Thus,individualplantsthatproduced morenutrientrichseedcoatsbeneficialtoantshadgreaterfitnessandwereselectedforoverseedswithless nutrientrichseedcoats.
