Chapter 02PROPERTIES OF POPULATIONS.docx
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Chapter 02PROPERTIES OF POPULATIONS.docx
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Chapter02PROPERTIESOFPOPULATIONS
Chapter02PROPERTIESOFPOPULATIONS(种群的基本特征)
Apopulationisagroupoforganismsofthesamespeciesoccupyingaparticularspaceatthesametime.
▪Samespecies
▪Samespace
▪Sametime
Populationshavetraitsthataredifferentfromthoseoftheindividualcomposingthepopulation.
∙Individualsarebornonce,dieonce,areeithermaleorfemale,youngorold.
∙Populationshavebirthrates,deathrates,andgrowthrates,havesexratios,agestructure,density,anddistributionintimeandspace.
1.UNITARYANDMODULARPOPULATIONS(单体生物与构件生物)
Anindividualisderivedfromonezygote.Whatisanindividualisnotalwaysclear.
Plantsderivedfromonezygotecanproducenewplantsormodulesasexuallybymeansofbudsonhallowhorizontalrootsorbystemsthattouchtheground.
▪Individualplantsproducedbysexualreproductionaregenets.
▪Asexuallyproducedindividualsderivedfromthegenericparentarecalledramets.
▪Agroupoframetsoriginatingfromthesamegenetmakesaclone.
Rametsmayremainlinkedtotheparentorexistindividually.
Examples:
a)Plantsasgrassclumps,blackberries,strawberries,thatreproduceasexuallyby
runnersorstolons.Oftenneverclearwhetheritsasinglemodularorganismora
ramet
b)Animalssuchascorals,hydroids,byrozoans,andtunicatesthatreproduceasexually
bybudding.Manyprimitivemetazoansarelooselyorganizedandformmodular
colonies.
c)Fungalmyceliaareinthesamecategory,Eachhyphaispotentiallyanorganism,but
themyceliumasagenetcanbeenormousinsize.
Allrametsarederivedfromthesamezygoteandmaybeconsideredasoneindividualorgenet.
Forpracticalreasons,inplantpopulationstudiesindividualrametsarecountedasandfunctionasindividualmembersofthepopulation.
2.METAPOPULATIONS(集合种群/META种群)
Partiallyisolatedgroupsofapopulationthatoccasionallyexchangeindividualsthroughimmigrationformametapopulation.
∙Thehabitatisfragmentedbyunsuitableareas.
∙Theareacanbeeasilyre-colonizedincaseofacatastrophe.
Thesubgroupsorsubpopulationshavetheirowndynamicsindependentofothersubpopulations:
birthanddeathrates.
Limiteddispersallinksthesubpopulations.
Individualsubpopulationshavefinitelifetime.
Islandsmaymaintainpopulationsderivedfromthemainland.Ifextinctionoccurs,theislandcouldberepopulatedfromthemainlandpopulation.
Localextinctionandrecolonizationallowmetapopulationstoexist.
3.POPULATIONSASGENETICUNITS(种群遗传特征)
Apopulationisageneticunit.
Genepool(种群基因库)isthesumofallthegenesinapopulation.
Evolutionfromageneticpointofviewisthechangeingenefrequenciesinagenepoolfromonetimetoalatertime.
Naturalselectionactsonthelessfavoredgenesanddecreasestheirfrequencyinthenextgeneration.
∙Thesegeneshavelowfitness.
Anoutcomeofthisselectionofgenesmaybechangesinthephysicalexpressionoforganisms.
4.DENSITYANDDISPERSION(密度和扩散)
CRUDEVERSUSECOLOGICALDENSITY
Densityisthenumberofindividualsperunitofspace(area,volume).Thiscalledcrudedensity.
Populationsareoftendiscussedintermsofdensity.
Habitatsareuniformlyhabitablebecauseofmicrodifferencesinlight,moisture,temperature,orexposure,tomentionafewconditions.
Eachorganismoccupiesonlyareasthatcanadequatelymeetitsrequirements,resultinginpatchdistribution.
Densitymeasureintermsoftheamountofareaavailableaslivingspaceisecologicaldensity.
Crudedensityincludesallthelandwithintheorganism'srangewhereasecologicaldensityincludesonlythatportionoflandthatcanactuallybecolonizedbythespecies.
Ecologicaldensityisrarelyusedbecauseofthedifficultyindeterminingwhatisalivablehabitat,andorganismsrequiredifferenthabitatsduringtheyearorduringtheirdevelopmentalchanges.
Usuallysmallerorganismsaremoreabundantthanlargerones.
Thetropicleveltheorganismoccupieshelpstodetermineitsdensity.
5.PATTERNSOFDISPERSION(空间扩散格局)
Spacialdispersion:
Spacingreferstothepositionofmembersofapopulationinreferencetoitsneighbors
1.Clumpedoraggregatespacingisthemostcommoninnature.
∙Causedbymicrohabitatpreference(e.g.shadedormoistplaces),dispersalpattern(e.g.rootshoots),socialbehaviorofanimals(e.g.flocking).
2.Evendistributionisrare;organismsareequidistantfromoneanother.
∙Causedbycompetition(e.g.territorialityofanimals,lackofsoilwaterinthedesert).
3.Randomspacingisrareinnature;spacingvariesbetweentheindividuals.
∙Theenvironmentisuniform,resourcesareevenlydistributedandavailablethroughouttheyear,andinteractionbetweenthemembersofthepopulationdoesnotcauseattractionoravoidance.
Apopulationmayshowonepatternatonescaleandanotherpatternatotherscale,e.g.largeherdsofantelope,wheretheanimalsareclumpedtogetheroverthegrasslandbutevenlyspacedfromoneanother.
6.Temporaldispersion(时间尺度上的扩散)
Organismsarealsodispersedintimeduetocircadianrhythms,changesinhumidityandtemperature,seasons,lunarcycles,andtidalcycles.
∙e.g.batsdispersinginthenightandregroupinginthecaveduringtheday;thereturnanddepartureofmigratinganimals.
7.Dispersalmovements(扩散运动形式)
Emigrationismovementoutofonehabitatandintoanother,immigration.
Dispersalwithareturntotheplaceoforiginiscalledmigration.
Plantsdependonpassivemeansofdispersal:
wind,water,animals,andgravity.
Somearebettermeansofdispersalthanothers.
Someanimalsalsodependonpassivetransportlikestreamandseacurrents,winddispersestheyoungofsomespiders.
Mostanimalsdisperseactivelybywalking,crawling,flying,andswimming.
∙Nataldispersaloccurswhentheyoungdisperse,likeinthecaseofmanybirds.
∙Breedingdispersaloccurswhenadultsdispersetofindbetterreproductivehabitats.
Thepre-reproductiveperiodistheusualtimeofdispersal.
Rodentsdispersewhenthepopulationhasincreasedandreachedapeak.Dispersaldeclineswhenthepopulationdeclines.
Animalswillsettleinfirstemptyandsuitablesite.Theyusuallytravelinstraightlinesandthensettle.
Someanimalspeciesmakeexploratorytripsaroundthenatalterritorybeforesettlingontheirterritory.
Migratorymovements
Migrationisaperiodicorseasonalmovementofanorganismorpopulationfromonehabitat,climate,orstratumtoanother.
Itusuallyinvolveslongdistanceandaffectstherangeofdistributionoftheindividualorpopulation.
Therearethreetypesofmigration:
1)Two-waymigrationeitherdailyorseasonal.
Examples:
∙Zooplanktonmovesdowntogreaterdepthduringtheday,andmovesupclosertothesurfacebynight.
∙Batsmoveoutofthecaveatnightandreturntoroostduringtheday.
Othermigrationsareseasonal:
∙Earthwormmovedeeperintosoilduringthewinterandmoveclosertothesurfaceinthespring.
∙Elkmovesdownthemountaininwinterandreturntohigheraltitudesinthespring.
2)Somemigrationsinvolveonlyonereturntrip,e.g.salmonspecies.
3)Inanothertypeofmigration,thefallmigrantsdonotreturnnorthbuttheiroffspringdo.Insectsthatmigrateinthiswayarethemonarchbutterfly,twospeciesofleafhoppers,harlequinbug,andthemilkweedbug.
8.AGESTRUCTURE(种群年龄结构)
Populationsoftenhaveindividualsofdifferentages.Thegroupingofmembersofapopulationbyageiscalledageddistributionoragestructure.
Agedistributionistypicallypresentedinamodifiedbarchartcalledalargepyramid.
Agedistributioncontributesinparttothereproductiverate,deathrate,vigor,survival,andotherdemographicattributes.
Severalcategoriescanbeusedtoanalyzetheagestructureofapopulation:
years,months,etc,,life-historystages(pre-reproductive,reproductiveandpost-reproductive;sizeclassesinherbaceousplants,treediameter,etc.Inplants,sizeisagoodpredictorofreproduction.
9.AGESTRUCTUREINANIMALS(动物种群年龄结构)
StableAgeDistribution:
Theagedistribution,whichthepopulationwillreachifallowedtoprogressuntilthereisnolongerachangeinthedistribution.
Agedistributioncanbedisruptedbyanaturalcatastrophe,disease,starvation,oremigration.
Stationaryornear-stationarypopulationpyramidsdisplaysomewhatequalnumbersorpercentagesforalmostallagegroups.
∙Birthsreplacedeathsandthepopulationisnotgrowing.
∙Ofcourse,smallerfiguresarestilltobeexpectedattheoldestagegroups.
∙Theage-sexdistributionsofsomeEuropeancountries,especiallyScandinavianones,willtendtofallintothiscategory.
Populationcanincrease,decreaseorremainstable.
Growingpopulationingeneralarecharacterizedbyalargenumberofyoung,givingthepyramidabroadbase.
Olderindividualsdominatenarrowpyramids.
Thelossofageclassescanhaveaprofoundinfluenceonapopulation'sfuture.
10.AGEDISTRIBUTIONINPLANTS(植物种群年龄结构)
Asexualreproductionandmodularstructureinplantspresentaprobleminanalyzingagestructure.
Ageinplantsisdeterminedbyfollowingacohortofindividualsoveraperiodoftime,orbydeterminingagebygrowthrings,budscars,orotherindicators.
Ineven-agedstandoftrees,individualsfallintoveryfewageclassesbecauseyoungageclassesareexcluded.
Competitionmaycauseasizedifferencebetweentreesofthesameage.Inthiscase,sizemaybemoreusefulthanage.
Seedbanksinthesoilpresentanotherproblem.Seedmayremainviableinthesoilformanyyears.Seedsthatgerminateinagivenyearmaybeofdifferentages.Whatistheageoftheplants?
10.SEXRATIOS(性比)
Mostpopu
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