APES Chapter 6 PDF
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This document appears to be a chapter from a book on population ecology. It discusses population abundance, distribution, growth models, and reproductive strategies. The chapter is likely part of an AP Environmental Science course.
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18 TheAbundanceandDistributionofPopulations 12-5 M LevelsofComplexity 1) Individual:Survivalandreproduction,naturalselection 2) Population:dynamicsandevolution 3) Community:interactionsamongandbetweenspecies...
18 TheAbundanceandDistributionofPopulations 12-5 M LevelsofComplexity 1) Individual:Survivalandreproduction,naturalselection 2) Population:dynamicsandevolution 3) Community:interactionsamongandbetweenspecies 4) Ecosystem:flowofmatterandenergy,cyclingofnutrients 5) Biosphere:globalprocesses,movementofair,water,andheat Populations-individualsthatdieandarebornandcanmovefromonepopulationtoanother BasicCharacteristics ○ Size(N)-thetotalnumberofindividualsinagivenarea ○ Density-thenumberofindividualsperunitareaatanygiventime;estimates whetheraspeciesisrareorabundant ○ Distribution-adescriptionofhowindividualsaredistributedtooneanother;this ishowpopulationsoccupyspace ○ SexRatio-malestofemales;mostsuccessfulwhen50:50butnotallareequal;we canpredictfuturepopulationsbasedonfemales ○ Agestructure-Howmanyindividualsfitaparticularagecategory;helpspredict howapopulationwillgrowordecrease DensityDependentFactors Gause’sExperimentwithtesttubecommunities Limitingresources-iftheylowerthepopulationwilllower(water,food,shelter, nutrients) CarryingCapacity(K)-thelimittohowmanyindividualsanenvironmentcansustain (dependentonlimitingfactors) DensityIndependentFactors Populationsizeisnotafactor ○ Withoutfactoringinlimitingresources ○ Withoutfactoringincarryingcapacity Thinkofweatherpatterns,naturaldisasters,anthropogenicdisasters,etc. M19 PopulationGrowthModels 12-5 Exponentialgrowthmodel-amodeloftheintrinsicgrowthrate(r)(maximumpotentialof growth) Populationthatcontinuouslygrow Idealconditions Unlimitedresources Highbirths,lowdeaths Nt=Noe rt ○ Nt- futuresize ○ No- currentsize ○ e-around2.72 ○ r-growthrate ○ t-time Populationsnotaffectedbyresources aredensity-independent ResultsinJ-shapedcurve LogisticGrowthModel PopulationsthatexperienceK(carryingcapacity) Growthhappensatafixedrate Limitingresources Initiallyexponential,butslowsasitreachesK Usedtopredictpopulationgrowthofdensity-dependentpopulations Doesnotaccountfordensity-independentfactors NumberofoffspringdependsonNt ResultsinS-shapedcurve Mayexperienceovershootsanddie0offs(ex.maltinginfall,birthinspring) ReproductiveStrategies K-SelectedSpecies ○ Lowintrinsicgrowthrates ○ PopulationslowsasitreachesK ○ Largerorganismsandmostbirds ○ Reproductivematurityisreachedlate ○ Producefewoffspring ○ Provideparentalcare ○ Ex.peopleandelephants R-SelectedSpecies(growthrate) ○ Highintrinsicrates ○ Experiencelargeovershootsanddie-offs ○ Reproduceoftenandinlargenumber ○ Tendtobesmallerorganisms ○ Reachreproductivematurityearly ○ Littletonoparentalcare ○ Ex.mice SurvivalshipCurves-patternsofsurvivalofindividualsovertime/lifespan TypeI TypeII TypeIII HighSurvivalrate Steadydeclineinsurvival Lowsurvivalrate Dieinlargenumbersinoldage Ex.squirrels Fewmakeittoadulthood K-selectedspecies R-selectedspecies Ex.humans Ex.mice Metapopulations Cougars-separated(allopatricspeciation)bylandmasses;eachpopulationisconsidered itsownspecies(mountains) ○ Cougarscanmovebetweenmountainrangesviacorridors(stripsofland connectingseparatedpopulations) ○ Eachspeciesofcougarisstillconnectedbythesemovementsandisknownas metapopulations Theconnectednessallowsforeachpopulation'spersistence ○ Smallpopulationsaremorelikelytogoextinctduetoahigherlikelihoodof experiencinginbreedingdepression(impairedabilitywheneachparentcarriesa harmfulgene)Lowergeneticdiversity ○ Smallpopulationsarealsomorevulnerabletonaturaldisasters Inmetapopulations,corridorsallowforeachspeciestogeneticdiversitytoanother M20 CommunityEcology 12-10 NegativeEffectsofCommunityEcology Studyofinteractionsamongspecies Symbioticrelationships Competition(-/-)-individualscompetingforthesamelimitedresources Predation(+/-)-predatorversusprey Parasitism(+/-)-liveson/inthehost,rarelycausesdeath(ex.tapeworm) Herbivory(+/-)-animalconsumesproducers CompetitiveExclusionPrinciple-twospeciescompetingforthesameresource;can’tcoexist Underagivensetofenvironmentalconditions,when2specieshavethesamerealized niche,onespecieswillperformbetterandwilldrivetheotherspeciestoextinction ResourcesPartitioning-2Specieswilldividearesourcebasedondifferencesinbehavioror morphology Wolfversuscoyote Desertplants Darwin’sfinches Parasitoids-atypeofpredation Layeggsinahostandwhentheyhatchthelarvaslowlyconsumesthehostfromthe insideout Parasitescancausediseaseinthehostcalledpathogens ○ Viruses ○ Bacterial ○ Fungal ○ Protists(protozoanoralgae) ○ Helminths(worm-likeorganisms) ○ Causesdiseasesfromcommoncoldstosomeformsofcancer Speciescanevolvetohavedefensesagainstpredator Behavioral(hiding) Morphological(camouflageex.waterfleas) Chemical(emitchemicals,ex.poisondartfrogs) Mimic(ex.poisonfrogvs.non-poison) Herbivorescanhavedramaticeffectsonproducers Tooabundantcankilloffspecies Iftheyareexclusivefromanarea,producerscanoverpopulate Neutral/PositiveEffects Mutualism(+/+)-bothbenefit(plantsandpollinators) ○ Bothbenefitandincreaseeachother'schancesofsurvival ○ I nmutualism,ifthebenefitofonepartybecomestoosmallitwillnolongerbe worththecostandnaturalselectionwilltakeover ○ Overgenerationsandthroughnaturalselectionorganismscanevolvetomake mutualismwork Commensalism(+/=)-benefitsonewithoutaffectingtheother ○ Ex.treesandbirdnests,coralreefsandfish TypeofInteraction Species1 Species2 Competition - - Predation + - Parasitism + - Herbivory + - Mutualism + + Commensalism + = Keystonespecies-notabundantbutsignificant Ex.beaversorhoneybees M21 CommunitySuccession 12-10 EcologicalSuccession Everycommunityexperiencesthis Canoccuroverdecadestocenturies 1) PrimarySuccession Beginwithrockandnosoil Newlyexposedrockbecauseofglacialretreat,lavacooling,abandonedparking lot Overtime, soilisformed,plantswithdeeprootsystemscanstarttogrow, grassesandwildflowersandwildflowerswilleasilydispersetotheseareas 2) SecondarySuccession Occursinareaswhereadisturbancehasoccurredbuthasnotlosttheirsoil Followseventssuchasforestfires,hurricanes,oragfieldsthathavebeenleft bare Pioneerspecieswillquicklygrowduetoallthesunlight,astheygrowandforma canopynewshade-tolerantspecieswillgrow SecondarySuccessionhappensonavastscalefromasingletreetothousandsof acresafteraforestfire 3) ClimaxCommunity ○ Successioninitsfinalstage AquaticEcosystemSuccession Rockyintertidalzones Majorstormsthatturnoverrocksorclearsurfacesoflivingthings,canberecognized Pondsandlakes:glacialmovements SpeciesRichness Speciesaren'tdistributedevenly Determinedby3basicprocesses ○ Colonization ○ Speciation ○ Lossesbyextension Importancesoftheseareinfluencedby ○ Latitude Aswemovehigherorlowertheequatorthenumberofspeciesdeclines Southernlatitudeshaveabout12,000species,NorthernCanada hasabout1,700 ○ Time Thelongerahabitatexiststhemorespeciescolonizationandextension occurs ○ SizeandDistance Largerhabitats=morespecies 1) Dispersingspeciesgenerallyseeklargerhabitats 2) Atanygivenlatitude,biggerhabitatsholdmore 3) Largehabitatsusuallyhaveawiderrangeofenvironmental conditions Habitatsthatareisolatedbylargedistanceswillhavelessspecies TheoryofIslandBiogeography Colonization,speciation,andextinctionhaveimportantimplicationsforconservation Thetheoryoriginallyappliedtooceanicislandsbutappliesto“habitatislandsEx. nationalparksorCentralPark Oftensurroundedbylesshospitablehabitatsthathavedramaticanthropogenic alterations
