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    Sunday,September23,2007

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    zoologygeneticdrift

    Geneticdrift

    Inpopulationgenetics,geneticdrift(ormorepreciselyallelicdrift)isthestatisticaleffectthatresultsfromtheinfluencethatchancehasonthesurvivalofalleles(variantsofagene).Theeffectmaycauseanallele,andthebiologicaltraitthatitconfers,tobecomemorecommonorrareoversuccessivegenerations.Ultimately,thedriftmayeitherremovetheallelefromthegenepoolorremoveallotheralleles.Whereasnaturalselectionisthetendencyofbeneficialallelestobecomemorecommonovertime(anddetrimentaloneslesscommon),geneticdriftisthefundamentaltendencyofanyalleletovaryrandomlyinfrequencyovertimeduetostatisticalvariationalone,solongasitdoesnotcompriseallornoneofthedistribution.

    Chanceaffectsthecommonalityorrarityofanallele,becausenotraitguaranteessurvivalofagivennumberofoffspring.Thisisbecausesurvivaldependsonnongeneticfactors(suchasthepossibilityofbeinginthewrongplaceatthewrongtime).Inotherwords,evenwhenindividualsfacethesameodds,theywilldifferintheirsuccess.Araresuccessionofchanceeventsratherthannaturalselectioncanthusbringatraittopredominance,causingapopulationorspeciestoevolve.

    Animportantaspectofgeneticdriftisthatitsrateisexpectedtodependstronglyonpopulationsizeasaconsequenceofthelawoflargenumbers.Whenmanyindividualscarryaparticularallele,andallfaceequalodds,thenumberofoffspringtheycollectivelyproducewillonlyslightlydifferfromthe

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    expectedvalue,whichistheexpectedaverageperindividualtimesthenumberofindividuals.Butwithasmalleffectivebreedingsize,adeparturefromthenorminoneindividualcausesadisproportionatelygreaterdeviationfromtheexpectedresult.Thereforesmallpopulationsaresubjecttomoredriftthanlargeones.Thisisalsothebasisforthefoundereffect,aproposedmechanismofspeciation.

    Bydefinition,geneticdrifthasnopreferreddirection.Aneutralallelemaybeexpectedtoincreaseordecreaseinanygivengenerationwithequalprobability.Givensufficientlylongtime,however,themathematicsofgeneticdrift(cf.GaltonWatsonprocess)predicttheallelewilleitherdieoutorbepresentin100%ofthepopulation,afterwhichtimethereisnorandomvariationintheassociatedgene.Thusgeneticdrifttendstosweepgenevariantsoutofapopulationovertime,suchthatallmembersofaspecieswouldeventuallybehomozygousforthisgene.Inthisregard,geneticdriftopposesgeneticmutationwhichintroducesnovelvariantsintothepopulationaccordingtoitsownrandomprocesses.

    Allelefrequencies

    Fromtheperspectiveofpopulationgenetics,driftisa"samplingeffect."Toillustrate:onaverage,coinsturnupheadsortailswithequalprobability.Yetjustafewtossesinarowareunlikelytoproduceheadsandtailsinequalnumber.Thenumbersarenomorelikelytobeexactlyequalformanytossesinarow,butthediscrepancyinnumbercanbeverysmall(inpercentageterms).Asanexample,tentossesturnupatleast70%headsaboutonceineverysixtries,butthechanceofahundredtossesinarowproducingatleast70%headsisonlyaboutonein25,000.

    Similarly,inabreedingpopulation,ifanallelehasafrequencyofp,probabilitytheorydictatesthat(ifnaturalselectionisnotacting)inthefollowinggeneration,afractionpofthepopulationwillinheritthatparticularallele.However,aswiththecointossabove,allelefrequenciesinrealpopulationsarenotprobabilitydistributionsrather,theyarearandomsample,andarethussubjecttothesamestatisticalfluctuations(samplingerror).

    Whentheallelesofagenedonotdifferwithregardtofitness,onaveragethenumberofcarriersinonegenerationisproportionaltothenumberofcarriersinthepreviousgeneration.Buttheaverageisnevertallied,becauseeachgenerationparentsthenextoneonlyonce.Thereforethefrequencyofanalleleamongtheoffspringoftendiffersfromitsfrequencyintheparentgeneration.Intheoffspringgeneration,theallelemightthereforehaveafrequencyp',slightlydifferentfromp.Inthissituation,theallelefrequenciesaresaidtohavedrifted.Notethatthefrequencyofthealleleinsubsequentgenerationswillnowbedeterminedbythenewfrequencyp',meaningthatdriftisamemorylessprocessandmaybemodeledasaMarkovprocess.

    Asinthecointossexampleabove,thesizeofthebreedingpopulation(theeffectivepopulationsize)governsthestrengthofthedrifteffect.Whentheeffectivepopulationsizeissmall,geneticdriftwillbestronger.

    Driftingallelesusuallyhaveafinitelifetime.Asthefrequencyofanalleledriftsupanddownoversuccessivegenerations,eventuallyitdriftsuntilfixationthatis,iteitherreachesafrequencyofzero,anddisappearsfromthepopulation,oritreachesafrequencyof100%andbecomestheonlyalleleinthepopulation.Subsequenttothelatterevent,theallelefrequencycanonlychangebytheintroductionofanewallelebyanewmutation.

    Thelifetimeofanalleleisgovernedbytheeffectivepopulationsize.Inaverysmallpopulation,onlyafewgenerationsmightberequiredforgeneticdrifttoresultinfixation.Inalargepopulation,itwouldtakemanymoregenerations.Onaverage,anallelewillbefixedin4Negenerations,whereNeistheeffectivepopulationsize.

    AccordingtotheHardyWeinbergPrinciple,whichholdsthatallelefrequenciesinagenepoolwillnotchangeovertime,apopulationmustbesufficientlylargetopreventgeneticdriftfromchangingallelefrequenciesovertime.Thisiswhythelawisunstableinasmallpopulation.

    Driftversusselection

    Geneticdriftandnaturalselectionrarelyoccurinisolationfromeachotherbothforcesarealwaysatplayinapopulation.However,thedegreetowhichallelesareaffectedbydriftandselectionvariesaccordingtocircumstance.

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    Inalargepopulation,wheregeneticdriftoccursveryslowly,evenweakselectiononanallelewillpushitsfrequencyupwardsordownwards(dependingonwhetherthealleleisbeneficialorharmful).However,ifthepopulationisverysmall,driftwillpredominate.Inthiscase,weakselectiveeffectsmaynotbeseenatallasthesmallchangesinfrequencytheywouldproduceareovershadowedbydrift.

    Geneticdriftinpopulations

    Driftcanhaveprofoundandoftenbizarreeffectsontheevolutionaryhistoryofapopulation.Theseeffectsmaybeatoddswiththesurvivalofthepopulation.

    Inapopulationbottleneck,wherethepopulationsuddenlycontractstoasmallsize(believedtohaveoccurredinthehistoryofhumanevolution),geneticdriftcanresultinsuddenanddramaticchangesinallelefrequencythatoccurindependentlyofselection.Insuchinstances,manybeneficialadaptationsmaybeeliminatedevenifpopulationlatergrowslargeagain.

    Similarly,migratingpopulationsmayseeafoundereffect,whereafewindividualswithararealleleintheoriginatinggenerationcanproduceapopulationthathasallelefrequenciesthatseemtobeatoddswithnaturalselection.Founder'seffectsaresometimesheldtoberesponsibleforhighfrequenciesofsomegeneticdiseases.

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    Sunday,September23,2007

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    zoologynitrogencycle

    TheNitrogenCycle

    Allliferequiresnitrogencompounds,e.g.,proteinsandnucleicacids.Air,whichis79%nitrogengas(N2),isthemajorreservoirofnitrogen.Butmostorganismscannotusenitrogeninthisform.

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    Plantsmustsecuretheirnitrogenin"fixed"form,i.e.,incorporatedincompoundssuchas:

    nitrateions(NO3)ammonia(NH3)urea(NH2)2CO

    Animalssecuretheirnitrogen(andallother)compoundsfromplants(oranimalsthathavefedonplants).

    Fourprocessesparticipateinthecyclingofnitrogenthroughthebiosphere:

    1.nitrogenfixation2.decay3.nitrification4.denitrification

    Microorganismsplaymajorrolesinallfourofthese.

    NitrogenFixation

    Thenitrogenmolecule(N2)isquiteinert.Tobreakitapartsothatitsatomscancombinewithotheratomsrequirestheinputofsubstantialamountsofenergy.

    Threeprocessesareresponsibleformostofthenitrogenfixationinthebiosphere:

    AtmosphericfixationbylightningBiologicalfixationbycertainmicrobesaloneorinasymbioticIndustrialfixation

    AtmosphericFixation

    Theenormousenergyoflightningbreaksnitrogenmoleculesandenablestheiratomstocombinewithoxygenintheairformingnitrogenoxides.Thesedissolveinrain,formingnitrates,thatarecarriedtotheearth.

    Atmosphericnitrogenfixationprobablycontributessome58%ofthetotalnitrogenfixed.

    IndustrialFixation

    Undergreatpressure,atatemperatureof600C,andwiththeuseofacatalyst,atmosphericnitrogenandhydrogen(usuallyderivedfromnaturalgasorpetroleum)canbecombinedtoformammonia(NH3).Ammoniacanbeuseddirectlyasfertilizer,butmostofitsisfurtherprocessedtoureaandammoniumnitrate(NH4NO3).

    BiologicalFixation

    Theabilitytofixnitrogenisfoundonlyincertainbacteriaandarchaea.

    Someliveinasymbioticrelationshipwithplantsofthelegumefamily(e.g.,soybeans,alfalfa).

    Someestablishsymbioticrelationshipswithplantsotherthanlegumes(e.g.,alders).

    Someestablishsymbioticrelationshipswithanimals,e.g.,termitesand"shipworms"(woodeatingbivalves).

    Somenitrogenfixingbacterialivefreeinthesoil.

    Nitrogenfixingcyanobacteriaareessentialtomaintainingthefertilityofsemiaquaticenvironmentslikericepaddies.

    BiologicalnitrogenfixationrequiresacomplexsetofenzymesandahugeexpenditureofATP.

    Althoughthefirststableproductoftheprocessisammonia,thisisquicklyincorporatedintoprotein

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    andotherorganicnitrogencompounds.

    Decay

    Theproteinsmadebyplantsenterandpassthroughfoodwebsjustascarbohydratesdo.Ateachtrophiclevel,theirmetabolismproducesorganicnitrogencompoundsthatreturntotheenvironment,chieflyinexcretions.Thefinalbeneficiariesofthesematerialsaremicroorganismsofdecay.Theybreakdownthemoleculesinexcretionsanddeadorganismsintoammonia.

    Nitrification

    Ammoniacanbetakenupdirectlybyplantsusuallythroughtheirroots.However,mostoftheammoniaproducedbydecayisconvertedintonitrates.Thisisaccomplishedintwosteps:

    BacteriaofthegenusNitrosomonasoxidizeNH3tonitrites(NO2).

    BacteriaofthegenusNitrobacteroxidizethenitritestonitrates(NO3).Thesetwogroupsofautotrophicbacteriaarecallednitrifyingbacteria.Throughtheiractivities

    (whichsupplythemwithalltheirenergyneeds),nitrogenismadeavailabletotherootsofplants.

    Manysoilsalsocontainarchaealmicrobes,assignedtotheCrenarchaeota,thatconvertammoniatonitrites.Whilemoreabundantthanthenitrifyingbacteria,itremainstobeseenwhethertheyplayasimportantaroleinthenitrogencycle.

    Manylegumes,inadditiontofixingatmosphericnitrogen,alsoperformnitrificationconvertingsomeoftheirorganicnitrogentonitritesandnitrates.Thesereachthesoilwhentheyshedtheirleaves.

    Denitrification

    Thethreeprocessesaboveremovenitrogenfromtheatmosphereandpassitthroughecosystems.

    Denitrificationreducesnitratestonitrogengas,thusreplenishingtheatmosphere.

    Onceagain,bacteriaaretheagents.Theylivedeepinsoilandinaquaticsedimentswhereconditionsareanaerobic.Theyusenitratesasanalternativetooxygenforthefinalelectronacceptorintheirrespiration.

    Thustheyclosethenitrogencycle.

    Arethedenitrifierskeepingup?

    Agriculturemaynowberesponsibleforonehalfofthenitrogenfixationonearththrough

    theuseoffertilizersproducedbyindustrialfixationthegrowingoflegumeslikesoybeansandalfalfa.

    Thisisaremarkableinfluenceonanaturalcycle.

    Arethedenitrifierskeepingupthenitrogencycleinbalance?Probablynot.Certainly,thereareexamplesofnitrogenenrichmentinecosystems.Onetroublingexample:the"blooms"ofalgaeinlakesandriversasnitrogenfertilizersleachfromthesoilofadjacentfarms(andlawns).Theaccumulationofdissolvednutrientsinabodyofwateriscalledeutrophication.

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    zoologycellbiomitochondria

    Mitochondria

    Mitochondriaarerodshapedorganellesthatcanbeconsideredthepowergeneratorsofthecell,convertingoxygenandnutrientsintoadenosinetriphosphate(ATP).ATPisthechemicalenergy"currency"ofthecellthatpowersthecell'smetabolicactivities.Thisprocessiscalledaerobic

    respirationandisthereasonanimalsbreatheoxygen.Withoutmitochondria(singular,mitochondrion),higheranimalswouldlikelynotexistbecausetheircellswouldonlybeabletoobtain

    energyfromanaerobicrespiration(intheabsenceofoxygen),aprocessmuchlessefficientthanaerobicrespiration.Infact,mitochondriaenablecellstoproduce15timesmoreATPthantheycouldotherwise,andcomplexanimals,likehumans,needlargeamountsofenergyinordertosurvive.

    Thenumberofmitochondriapresentinacelldependsuponthemetabolicrequirementsofthatcell,andmayrangefromasinglelargemitochondriontothousandsoftheorganelles.Mitochondria,whicharefoundinnearlyalleukaryotes,includingplants,animals,fungi,andprotists,arelargeenoughtobeobservedwithalightmicroscopeandwerefirstdiscoveredinthe1800s.Thenameoftheorganelleswascoinedtoreflectthewaytheylookedtothefirstscientiststoobservethem,stemmingfromtheGreekwordsfor"thread"and"granule."Formanyyearsaftertheirdiscovery,mitochondriawerecommonlybelievedtotransmithereditaryinformation.Itwasnotuntilthemid1950swhenamethodforisolatingtheorganellesintactwasdevelopedthatthemodernunderstandingofmitochondrialfunctionwasworkedout.Theelaboratestructureofamitochondrionisveryimportanttothefunctioningoftheorganelle.Twospecializedmembranesencircleeachmitochondrionpresentinacell,dividingtheorganelleintoanarrowintermembranespaceandamuchlargerinternalmatrix,eachofwhichcontainshighlyspecializedproteins.Theoutermembraneofamitochondrioncontainsmanychannelsformedbytheproteinporinandactslikeasieve,filteringoutmoleculesthataretoobig.Similarly,theinnermembrane,whichishighlyconvolutedsothatalargenumberofinfoldingscalledcristaeareformed,alsoallowsonlycertainmoleculestopassthroughitandismuchmoreselectivethantheoutermembrane.Tomakecertainthatonlythosematerialsessentialtothematrixareallowedintoit,theinnermembraneutilizesagroupoftransportproteinsthatwillonlytransportthecorrectmolecules.Together,thevariouscompartmentsofamitochondrionareabletoworkinharmonytogenerateATPinacomplexmultistepprocess.Mitochondriaaregenerallyoblongorganelles,whichrangeinsizebetween1and10micrometersinlength,andoccurinnumbersthatdirectlycorrelatewiththecell'slevelofmetabolicactivity.Theorganellesarequiteflexible,however,andtimelapsestudiesoflivingcellshavedemonstratedthatmitochondriachangeshaperapidlyandmoveaboutinthecellalmostconstantly.Movementsoftheorganellesappeartobelinkedinsomewaytothemicrotubulespresentinthecell,andareprobablytransportedalongthenetworkwithmotorproteins.Consequently,mitochondriamaybeorganizedintolengthytravelingchains,packedtightlyintorelativelystablegroups,orappearinmanyotherformationsbasedupontheparticularneedsofthecellandthecharacteristicsofitsmicrotubularnetwork.ThemitochondrionisdifferentfrommostotherorganellesbecauseithasitsowncircularDNA(similartotheDNAofprokaryotes)andreproducesindependentlyofthecellinwhichitisfoundanapparentcaseofendosymbiosis.Scientistshypothesizethatmillionsofyearsagosmall,freelivingprokaryoteswereengulfed,butnotconsumed,bylargerprokaryotes,perhapsbecausetheywereabletoresistthedigestiveenzymesofthehostorganism.Thetwoorganismsdevelopedasymbioticrelationshipovertime,thelargerorganismprovidingthesmallerwithamplenutrientsandthesmallerorganismprovidingATPmoleculestothelargerone.Eventually,accordingtothisview,thelargerorganismdevelopedintotheeukaryoticcellandthesmallerorganismintothemitochondrion.MitochondrialDNAislocalizedtothematrix,whichalsocontainsahostofenzymes,aswellas

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    ribosomesforproteinsynthesis.Manyofthecriticalmetabolicstepsofcellularrespirationarecatalyzedbyenzymesthatareabletodiffusethroughthemitochondrialmatrix.Theotherproteinsinvolvedinrespiration,includingtheenzymethatgeneratesATP,areembeddedwithinthemitochondrialinnermembrane.Infoldingofthecristaedramaticallyincreasesthesurfaceareaavailableforhostingtheenzymesresponsibleforcellularrespiration.

    Mitochondriaaresimilartoplantchloroplastsinthatbothorganellesareabletoproduceenergyandmetabolitesthatarerequiredbythehostcell.Asdiscussedabove,mitochondriaarethesitesofrespiration,andgeneratechemicalenergyintheformofATPbymetabolizingsugars,fats,andotherchemicalfuelswiththeassistanceofmolecularoxygen.Chloroplasts,incontrast,arefoundonlyinplantsandalgae,andaretheprimarysitesofphotosynthesis.Theseorganellesworkinadifferentmannertoconvertenergyfromthesunintothebiosynthesisofrequiredorganicnutrientsusingcarbondioxideandwater.Likemitochondria,chloroplastsalsocontaintheirownDNAandareabletogrowandreproduceindependentlywithinthecell.Inmostanimalspecies,mitochondriaappeartobeprimarilyinheritedthroughthematernallineage,thoughsomerecentevidencesuggeststhatinrareinstancesmitochondriamayalsobeinheritedviaapaternalroute.Typically,aspermcarriesmitochondriainitstailasanenergysourceforitslongjourneytotheegg.Whenthespermattachestotheeggduringfertilization,thetailfallsoff.Consequently,theonlymitochondriatheneworganismusuallygetsarefromtheeggitsmotherprovided.Therefore,unlikenuclearDNA,mitochondrialDNAdoesn'tgetshuffledeverygeneration,soitispresumedtochangeataslowerrate,whichisusefulforthestudyofhumanevolution.MitochondrialDNAisalsousedinforensicscienceasatoolforidentifyingcorpsesorbodyparts,andhasbeenimplicatedinanumberofgeneticdiseases,suchasAlzheimer'sdiseaseanddiabetes

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    zoologyEcosystem

    WhatisaBiome?

    Abiomeisalargegeographicalareaofdistinctiveplantandanimalgroups,whichareadaptedtothatparticularenvironment.Theclimateandgeographyofaregiondetermineswhattypeofbiomecanexistinthatregion.Majorbiomesincludedeserts,forests,grasslands,tundra,andseveraltypesofaquaticenvironments.Eachbiomeconsistsofmanyecosystemswhosecommunitieshaveadaptedtothesmalldifferencesinclimateandtheenvironmentinsidethebiome.Alllivingthingsarecloselyrelatedtotheirenvironment.Anychangeinonepartofanenvironment,likeanincreaseordecreaseofaspeciesofanimalorplant,causesarippleeffectofchangeinthroughotherpartsoftheenvironment.Theearthincludesahugevarietyoflivingthings,fromcomplexplantsandanimalstoverysimple,onecelledorganisms.Butlargeorsmall,simpleorcomplex,noorganismlivesalone.Eachdependsinsomewayonotherlivingandnonlivingthingsinitssurroundings.

    Deciduousforests

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    DeciduousforestscanbefoundintheeasternhalfofNorthAmerica,andthemiddleofEurope.TherearemanydeciduousforestsinAsia.SomeofthemajorareasthattheyareinaresouthwestRussia,Japan,andeasternChina.SouthAmericahastwobigareasofdeciduousforestsinsouthernChileandMiddleEastcoastofParaguay.TherearedeciduousforestslocatedinNewZealand,andsoutheasternAustraliaalso.

    Theaverageannualtemperatureinadeciduousforestis50F.Theaveragerainfallis30to60inchesayear.

    Indeciduousforeststherearefivedifferentzones.ThefirstzoneistheTreeStratumzone.TheTreeStratumzonecontainssuchtreesasoak,beech,maple,chestnuthickory,elm,basswood,linden,walnut,andsweetgumtrees.Thiszonehasheightrangesbetween60feetand100feet.

    Thesmalltreeandsaplingzoneisthesecondzone.Thiszonehasyoung,andshorttrees.Thethirdzoneiscalledtheshrubzone.Someoftheshrubsinthiszonearerhododendrons,azaleas,mountainlaurel,andhuckleberries.TheHerbzoneisthefourthzone.Itcontainsshortplantssuchasherbalplants.ThefinalzoneistheGroundzone.Itcontainslichen,clubmosses,andtruemosses.

    Thedeciduousforesthasfourdistinctseasons,spring,summer,autumn,andwinter.Intheautumntheleaveschangecolor.Duringthewintermonthsthetreeslosetheirleaves.

    Theanimalsadapttotheclimatebyhibernatinginthewinterandlivingoffthelandintheotherthreeseasons.Theanimalshaveadaptedtothelandbytryingtheplantsintheforesttoseeiftheyaregoodtoeatforagoodsupplyoffood.Alsothetreesprovideshelterforthem.Animalusethetreesforfoodandawatersources.Mostoftheanimalsarecamouflagedtolookliketheground.Theplantshaveadaptedtotheforestsbyleaningtowardthesun.Soakingupthenutrientsinthegroundisalsoawayofadaptation.

    Alotofdeciduousforestshavelostlandtofarmsandtowns.Althoughpeoplearetryingtoprotecttheforestssomepoachersaretryingtokilltheanimalsintheforests.Theanimalsarelosingtheirhomesbecauseofpeoplebuildingtheirhomes.

    DESERTECOSYSTEM.

    AHotandDryDesertis,asyoucantellfromthename,hotanddry.MostHotandDryDesertsdon'thaveverymanyplants.Theydohavesomelowdownplantsthough.Theonlyanimalstheyhavethatcansurvivehavetheabilitytoburrowunderground.Thisisbecausetheywouldnotbeabletoliveinthehotsunandheat.Theyonlycomeoutinthenightwhenitisalittlecooler.

    AcolddesertisadesertthathassnowinthewinterinsteadofjustdroppingafewdegreesintemperatureliketheywouldinaHotandDryDesert.Itnevergetswarmenoughforplantstogrow.Justmaybeafewgrassesandmosses.TheanimalsinColdDesertsalsohavetoburrowbutinthiscasetokeepwarm,notcool.ThatiswhyyoumightfindsomeofthesameanimalshereasyouwouldintheHotandDryDeserts.

    DesertscoveraboutonefifthoftheEarth'slandsurface.MostHotandDryDesertsareneartheTropicofCancerortheTropicofCapricorn.ColdDesertsareneartheArcticpartoftheworld.HotandDryDesertstemperaturerangesfrom20to25C.TheextrememaximumtemperatureforHotDesertrangesfrom43.5to49C.ColdDesertstemperatureinwinterrangesfrom2to4Candinthesummer21to26CayearTheprecipitationinHotandDryDesertsandtheprecipitationinColdDesertsisdifferent.HotandDryDesertsusuallyhaveverylittlerainfalland/orconcentratedrainfallinshortperiodsbetweenlongrainlessperiods.Thisaveragesouttounder15cmayear.ColdDesertsusuallyhavelotsofsnow.Theyalsohaverainaroundspring.Thisaveragesoutto1526cmayear.

    HotandDryDesertsarewarmthroughoutthefallandspringseasonsandveryhotduringthesummer.thewintersusuallyhaveverylittleifanyrainfall.ColdDesertshavequiteabitofsnowduringwinter.Thesummerandthebeginningofthespringarebarelywarmenoughforafewlichens,grassesandmossestogrow.HotandDryDesertsvegetationisveryrare.Plantsarealmostallgroundhuggingshrubsandshortwoodytrees.Alloftheleavesarereplete(packedwithnutrients).SomeexamplesofthesekindsofplantareTurpentineBush,PricklyPears,andBrittleBush.Foralloftheseplantstosurvivetheyhavetohaveadaptations.Someoftheadaptationsinthiscasearetheabilitytostorewaterforlongperiodsoftimeandtheabilitytostandthehotweather.

    ColdDesert'splantsarescattered.Inareaswithlittleshade,about10percentofthegroundiscoveredwithplants.Insomeareasofsagebrushitreaches85percent.Theheightofscrubvariesfrom15cmto122cm.Allplantsareeitherdeciduousandmoreorlesscontainspinyleaves.

    HotandDryDesertsanimalsincludesmallnocturnal(onlyactiveatnight)carnivores.Therearealsoinsects,

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    arachnids,reptiles,andbirds.SomeexamplesoftheseanimalsareBorrowers,MourningWheatears,andHornedVipers.ColdDesertshaveanimalslikeAntelope,GroundSquirrels,JackRabbits,andKangarooRats.

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    Grasslandecosytem

    GrasslandEcosystem

    Grasslandbiomesarelarge,rollingterrainsofgrasses,flowersandherbs.Latitude,soilandlocalclimatesforthemostpartdeterminewhatkindsofplantsgrowinaparticulargrassland.Agrasslandisaregionwheretheaverageannualprecipitationisgreatenoughtosupportgrasses,andinsomeareasafewtrees.Theprecipitationissoeraticthatdroughtandfirepreventlargeforestsfromgrowing.Grassescansurvivefiresbecausetheygrowfromthebottominsteadofthetop.Theirstemscangrowagainafterbeingburnedoff.Thesoilofmostgrasslandsisalsotoothinanddryfortreestosurvive.

    WhenthesettlersoftheUnitedStatesmovedwestward,theyfoundthatthegrasslands,orprairiesastheycalledthem,weremorethanjustdry,flatareas.Theprairiescontainedmorethan80speciesofanimalsand300speciesofbirds,andhundredsofspeciesofplants.

    Therearetwodifferenttypesofgrasslandstallgrass,whicharehumidandverywet,andshortgrass,whicharedry,withhottersummersandcolderwintersthanthetallgrassprairie.Thesettlersfoundbothontheirjourneywest.WhentheycrossedtheMississippiRivertheycameintosomeverytallgrass,someashighas11feet.Hereitrainedquiteoftenanditwasveryhumid.AstheytraveledfurtherwestandapproachedtheRockyMountains,thegrassbecameshorter.Therewaslessraininthesummerandthewintersgotcolder.Theseweretheshortgrassprairies.

    Grasslandbiomescanbefoundinthemiddlelatitudes,intheinteriorsofcontinents.Theycanhaveeithermoistcontinentalclimatesordrysubtropicalclimates.InArgentina,SouthAmerica,thegrasslandsareknownaspampas.Theclimatethereishumidandmoist.Grasslandsinthesouthernhemispheretendtogetmoreprecipitationthanthoseinthenorthernhemisphere,andthegrasstendstobethetallgrassvariety.

    ThereisalargeareaofgrasslandthatstretchfromtheUkraineofRussiaallthewaytoSiberia.Thisisaverycoldanddryclimatebecausethereisnonearbyoceantogetmoisturefrom.Windsfromthearcticaren'tblockedbyanymountainseither.TheseareknownastheRussianandAsiansteppes.Inthewinter,grasslandtemperaturescanbeaslowas40F,andinthesummeritcanbeashigh70F.Therearetworealseasons:agrowingseasonandadormantseason.Thegrowingseasoniswhenthereisnofrostandplantscangrow(whichlastsfrom100to175days).Duringthedormant(notgrowing)seasonnothingcangrowbecauseitstoocold.

    Intropicalandsubtropicalgrasslandsthelengthofthegrowingseasonisdeterminedbyhowlongtherainyseasonlasts.Butinthetemperategrasslandsthelengthofthegrowingseasonisdeterminedbytemperature.Plantsusuallystartgrowingwhenthedailytemperaturereachedabout50F.Intemperategrasslandstheaveragerainfallperyearrangesfrom1030inches.Intropicalandsubtropicalgrasslandstheaveragerainfallperyearrangesfrom2560inchesperyearTheamountofrainfallisveryimportantindeterminingwhichareasaregrasslandsbecauseit'shardfortreestocompetewithgrassesinplaceswheretheupperslayersofsoilaremoistduringpartoftheyearbutwheredeeperlayerofsoilarealwaysdry.

    ThemostcommontypesofplantlifeontheNorthAmericanprairieareBuffaloGrass,Sunflower,CrazyWeed,Asters,BlazingStars,Coneflowers,Goldenrods,Clover,andWildIndigos.

    SomecommonanimalsinthegrasslandsareCoyotes,Eagles,Bobcats,theGrayWolf,WildTurkey,FlyCatcher,CanadianGeese,Crickets,DungBeetle,Bison,andPrairieChicken.

    LasteditedbyXericFriday,May15,2009at08:28PM.

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    #6

    TheFollowingUserSaysThankYoutoAFRMSForThisUsefulPost:farheen79(Monday,August26,2013)

    Friday,October05,2007

    AFRMS37thCommon

    JoinDate:Mar2006Posts:1,514Thanks:1,053Thanked1,670Timesin871Posts

    TaigaandRainforestecosystem

    RainforestEcosystem

    Thetropicalrainforestcanbefoundinthreemajorgeographicalareasaroundtheworld.CentralAmericainthetheAmazonriverbasin.AfricaZairebasin,withasmallareainWestAfricaalsoeasternMadagascar.IndoMalaysiawestcoastofIndia,Assam,SoutheastAsia,NewGuineaandQueensland,Australia.

    Thetropicalrainforestisaforestoftalltreesinaregionofyearroundwarmth.Anaverageof50to260inches(125to660cm.)ofrainfallsyearly.Rainforestsbelongtothetropicalwetclimategroup.Thetemperatureinarainforestrarelygetshigherthan93F(34C)ordropsbelow68F(20C)averagehumidityisbetween77and88%rainfallisoftenmorethan100inchesayear.Thereisusuallyabriefseasonoflessrain.Inmonsoonalareas,thereisarealdryseason.Almostallrainforestslieneartheequator.

    Rainforestsnowcoverlessthan6%ofEarth'slandsurface.Scientistsestimatethatmorethanhalfofalltheworld'splantandanimalspeciesliveintropicalrainforests.Tropicalrainforestsproduce40%ofEarth'soxygen.

    Atropicalrainforesthasmorekindsoftreesthananyotherareaintheworld.Scientistshavecountedabout100to300speciesinone21/2acre(1hectare)areainSouthAmerica.Seventypercentoftheplantsintherainforestaretrees.About1/4ofallthemedicinesweusecomefromrainforestplants.Curarecomesfromatropicalvine,andisusedasananestheticandtorelaxmusclesduringsurgery.Quinine,fromthecinchonatree,isusedtotreatmalaria.Apersonwithlymphocyticleukemiahasa99%chancethatthediseasewillgointoremissionbecauseoftherosyperiwinkle.Morethan1,400varietiesoftropicalplantsarethoughttobepotentialcuresforcancer.

    Alltropicalrainforestsresembleoneanotherinsomeways.Manyofthetreeshavestraighttrunksthatdon'tbranchoutfor100feetormore.Thereisnosenseingrowingbranchesbelowthecanopywherethereislittlelight.Themajorityofthetreeshavesmooth,thinbarkbecausethereisnoneedtoprotectthethemfromwaterlossandfreezingtemperatures.Italsomakesitdifficultforepiphytesandplantparasitestogetaholdonthetrunks.Thebarkofdifferentspeciesissosimilarthatitisdifficulttoidentifyatreebyitsbark.Manytreescanonlybeidentifiedbytheirflowers.

    Despitethesedifferences,eachofthethreelargestrainforeststheAmerican,theAfrican,andtheAsianhasadifferentgroupofanimalandplantspecies.Eachrainforesthasmanyspeciesofmonkeys,allofwhichdifferfromthespeciesoftheothertworainforests.Inaddition,differentareasofthesamerainforestmayhavedifferentspecies.ManykindsoftreesthatgrowinthemountainsoftheAmazonrainforestdonotgrowinthelowlandsofthatsameforest.

    LayersoftheRainforest

    Therearefourverydistinctlayersoftreesinatropicalrainforest.Theselayershavebeenidentifiedastheemergent,uppercanopy,understory,andforestfloor.Emergenttreesarespacedwideapart,andare100to240feettallwithumbrellashapedcanopiesthatgrowabovetheforest.Becauseemergenttreesareexposedtodryingwinds,theytendtohavesmall,pointedleaves.Somespecieslosetheirleavesduringthebriefdryseasoninmonsoonrainforests.Thesegianttreeshavestraight,smoothtrunkswithfewbranches.Theirrootsystemisveryshallow,andtosupporttheirsizetheygrowbuttressesthatcanspreadouttoadistanceof30feet.

    Theuppercanopyof60to130foottreesallowslighttobeeasilyavailableatthetopofthislayer,butgreatlyreducedanylightbelowit.Mostoftherainforest'sanimalsliveintheuppercanopy.Thereissomuchfoodavailableatthislevelthatsomeanimalsnevergodowntotheforestfloor.Theleaveshave"dripspouts"thatallowsraintorunoff.

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    Thiskeepsthemdryandpreventsmoldandmildewfromforminginthehumidenvironment.

    Theunderstory,orlowercanopy,consistsof60foottrees.Thislayerismadeupofthetrunksofcanopytrees,shrubs,plantsandsmalltrees.Thereislittleairmovement.Asaresultthehumidityisconstantlyhigh.Thislevelisinconstantshade.

    Theforestfloorisusuallycompletelyshaded,exceptwhereacanopytreehasfallenandcreatedanopening.Mostareasoftheforestfloorreceivesolittlelightthatfewbushesorherbscangrowthere.Asaresult,apersoncaneasilywalkthroughmostpartsofatropicalrainforest.Lessthan1%ofthelightthatstrikesthetopoftheforestpenetratestotheforestfloor.Thetopsoilisverythinandofpoorquality.Alotoflitterfallstothegroundwhereitisquicklybrokendownbydecomposersliketermites,earthwormsandfungi.Theheatandhumidityfurtherhelptobreakdownthelitter.Thisorganicmatteristhenjustasquicklyabsorbedbythetrees'shallowroots.

    PlantLife

    Besidesthesefourlayers,ashrub/saplinglayerreceivesabout3%ofthelightthatfiltersinthroughthecanopies.Thesestuntedtreesarecapableofasuddengrowthsurgewhenagapinthecanopyopensabovethem.

    Theairbeneaththelowercanopyisalmostalwayshumid.Thetreesthemselvesgiveoffwaterthroughthepores(stomata)oftheirleaves.Thisprocess,calledtranspiration,canaccountforasmuchashalfoftheprecipitationintherainforest.

    Rainforestplantshavemademanyadaptationstotheirenvironment.Withover80inchesofrainperyear,plantshavemadeadaptationsthathelpsthemshedwaterofftheirleavesquicklysothebranchesdon'tgetweigheddownandbreak.Manyplantshavedriptipsandgroovedleaves,andsomeleaveshaveoilycoatingstoshedwater.Toabsorbasmuchsunlightaspossibleonthedarkunderstory,leavesareverylarge.Sometreeshaveleafstalksthatturnwiththemovementofthesunsotheyalwaysabsorbthemaximumamountoflight.Leavesintheuppercanopyaredarkgreen,smallandleatherytoreducewaterlossinthestrongsunlight.Sometreeswillgrowlargeleavesatthelowercanopylevelandsmallleavesintheuppercanopy.Otherplantsgrowintheuppercanopyonlargertreestogetsunlight.Thesearetheepiphytessuchasorchidsandbromeliads.Manytreeshavebuttressandstiltrootsforextrasupportintheshallow,wetsoiloftherainforests.

    Over2,500speciesofvinesgrowintherainforest.Lianasstartoffassmallshrubsthatgrowontheforestfloor.Toreachthesunlightintheuppercanopyitsendsouttendrilstograbsaplingtrees.Thelianaandthetreegrowtowardsthecanopytogether.Thevinesgrowfromonetreetoanotherandmakeup40%ofthecanopyleaves.Therattanvinehasspikesontheundersideofitsleavesthatpointbackwardstograbontosaplingtrees.Other"strangler"vineswillusetreesassupportandgrowthickerandthickerastheyreachthecanopy,stranglingitshosttree.Theylookliketreeswhosecentershavebeenhollowedout.

    Dominantspeciesdonotexistintropicalrainforests.LowlanddipterocarpforestcanconsistofmanydifferentspeciesofDipterocarpaceae,butnotallofthesamespecies.Treesofthesamespeciesareveryseldomfoundgrowingclosetogether.Thisbiodiversityandseparationofthespeciespreventsmasscontaminationanddieofffromdiseaseorinsectinfestation.Biodiversityalsoinsuresthattherewillbeenoughpollinatorstotakecareofeachspecies'needs.Animalsdependonthestaggeredbloomingandfruitingofrainforestplantstosupplythemwithayearroundsourceoffood.

    AnimalLife

    Manyspeciesofanimallifecanbefoundintherainforest.Commoncharacteristicsfoundamongmammalsandbirds(andreptilesandamphibians,too)includeadaptationstoalifeinthetrees,suchastheprehensiletailsofNewWorldmonkeys.Othercharacteristicsarebrightcolorsandsharppatterns,loudvocalizations,anddietsheavyonfruits.

    Insectsmakeupthelargestsinglegroupofanimalsthatliveintropicalforests.Theyincludebrightlycoloredbutterflies,mosquitoes,camouflagedstickinsects,andhugecoloniesofants.

    TheAmazonriverbasinrainforestcontainsawidervarietyofplantandanimallifethananyotherbiomeintheworld.ThesecondlargestpopulationofplantandanimallifecanbefoundinscatteredlocationsandislandsofSoutheastAsia.ThelowestvarietycanbefoundinAfrica.Theremaybe40to100differentspeciesin2.5acres(1hectare)ofatropicalrainforest.

    TAIGAECOSYSTEM

    Abiomeisthetypeofhabitatincertainplaces,likemountaintops,deserts,andtropicalforests,andisdeterminedby

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    #7

    theclimateoftheplace.Thetaigaisthebiomeoftheneedleleafforest.Livinginthetaigaiscoldandlonely.Coldnessandfoodshortagesmakethingsverydifficult,mostlyinthewinter.Someoftheanimalsinthetaigahibernateinthewinter,someflysouthiftheycan,whilesomejustcooperatewiththeenvironment,whichisverydifficult.(DillonBartkus)TaigaistheRussianwordforforestandisthelargestbiomeintheworld.ItstretchesoverEurasiaandNorthAmerica.Thetaigaislocatednearthetopoftheworld,justbelowthetundrabiome.Thewintersinthetaigaareverycoldwithonlysnowfall.Thesummersarewarm,rainy,andhumid.Alotofconiferoustreesgrowinthetaiga.Thetaigaisalsoknownastheborealforest.DidyouknowthatBorealwastheGreekgoddessoftheNorthWind?

    Thetaigadoesn'thaveasmanyplantandanimalspeciesasthetropicalorthedeciduousforestbiomes.Itdoeshavemillionsofinsectsinthesummertime.Birdsmigratethereeveryyeartonestandfeed.

    Hereissomeinformationaboutthetemperaturesandweatherinthetaiga.Theaveragetemperatureisbelowfreezingforsixmonthsoutoftheyear.Thewintertemperaturerangeis54to1C(65to30F).Thewinters,asyoucansee,arereallycold,withlotsofsnow.

    Temperaturerangeinthesummergetsaslowas7C(20F).Thehighinsummercanbe21C(70F).Thesummersaremostlywarm,rainyandhumid.Theyarealsoveryshortwithabout50to100frostfreedays.Thetotalprecipitationinayearis3085cm(1233in).Theformstheprecipitationcomesinarerain,snowanddew.Mostoftheprecipitationinthetaigafallsasraininthesummer.

    Themainseasonsinthetaigaarewinterandsummer.Thespringandautumnaresoshort,youhardlyknowtheyexist.Itiseitherhotandhumidorverycoldinthetaiga.

    Therearenotalotofspeciesofplantsinthetaigabecauseoftheharshconditions.Notmanyplantscansurvivetheextremecoldofthetaigawinter.Therearesomelichensandmosses,butmostplantsareconiferoustreeslikepine,whitespruce,hemlockanddouglasfir.

    Coniferoustreesarealsoknownasevergreens.Theyhavelong,thinwaxyneedles.Thewaxgivesthemsomeprotectionfromfreezingtemperaturesandfromdryingout.Evergreensdon'tloosetheirleavesinthewinterlikedeciduoustrees.Theykeeptheirneedlesallyearlong.Thisissotheycanstartphotosynthesisassoonastheweathergetswarm.Thedarkcolorofevergreenneedlesallowsthemtoabsorbheatfromthesunandalsohelpsthemstartphotosynthesisearly.

    Evergreensinthetaigatendtobethinandgrowclosetogether.Thisgivesthemprotectionfromthecoldandwind.Evergreensalsoareusuallyshapedlikeanupsidedownconetoprotectsthebranchesfrombreakingundertheweightofallthatsnow.Thesnowslidesrightofftheslantedbranches.

    Thetaigaissusceptibletomanywildfires.Treeshaveadaptedbygrowingthickbark.Thefireswillburnawaytheuppercanopyofthetreesandletsunlightreachtheground.Newplantswillgrowandprovidefoodforanimalsthatoncecouldnotlivetherebecausetherewereonlyevergreentrees.

    Animalsofthetaigatendtobepredatorslikethelynxandmembersoftheweaselfamilylikewolverines,bobcat,minksandermine.Theyhuntherbivoreslikesnowshoerabbits,redsquirrelsandvoles.Reddeer,elk,andmoosecanbefoundinregionsofthetaigawheremoredeciduoustreesgrow.

    Manyinsecteatingbirdscometothetaigatobreed.Theyleavewhenthebreedingseasonisover.Seedeaterslikefinchesandsparrows,andomnivorousbirdslikecrowsstayallyearlong.

    LasteditedbyXericFriday,May15,2009at08:29PM.

    TheFollowingUserSaysThankYoutoAFRMSForThisUsefulPost:farheen79(Monday,August26,2013)

    Friday,October05,2007

    AFRMS37thCommon

    JoinDate:Mar2006Posts:1,514Thanks:1,053Thanked1,670Timesin871Posts

    Savanna,Alpine,chaparralecosystem

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    Savannaecosystem

    Asavannaisarollinggrasslandscatteredwithshrubsandisolatedtrees,whichcanbefoundbetweenatropicalrainforestanddesertbiome.Notenoughrainfallsonasavannatosupportforests.Savannasarealsoknownastropicalgrasslands.Theyarefoundinawidebandoneithersideoftheequatorontheedgesoftropicalrainforests.

    Savannashavewarmtemperatureyearround.Thereareactuallytwoverydifferentseasonsinasavannaaverylongdryseason(winter),andaverywetseason(summer).Inthedryseasononlyanaverageofabout4inchesofrainfalls.BetweenDecemberandFebruarynorainwillfallatall.Oddlyenough,itisactuallyalittlecoolerduringthisdryseason.Butdon'texpectsweaterweatheritisstillaround70F.

    Inthesummerthereislotsofrain.InAfricathemonsoonrainsbegininMay.Anaverageof15to25inchesofrainfallsduringthistime.Itgetshotandveryhumidduringtherainyseason.Everydaythehot,humidairrisesoffthegroundandcollideswithcoolerairaboveandturnsintorain.Intheafternoonsonthesummersavannatherainspourdownforhours.Africansavannashavelargeherdsofgrazingandbrowsinghoofedanimals.Eachanimalhasaspecializedeatinghabitthatreducescompititionforfood.Thereareseveraldifferenttypesofsavannasaroundtheworld.ThesavannaswearemostfamiliarwitharetheEastAfricansavannascoveredwithacaciatrees.TheSerengetiPlainsofTanzaniaaresomeofthemostwellknown.Hereanimalslikelions,zebras,elephants,andgiraffesandmanytypesofungulates(animalswithhooves)grazeandhunt.Manylargegrasseatingmammals(herbivores)cansurviveherebecausetheycanmovearoundandeattheplentifulgrasses.Therearealsolotsofcarnivores(meateaters)whoeattheminturn.

    SouthAmericaalsohassavannas,butthereareveryfewspeciesthatexistonlyonthissavanna.InBrazil,Colombia,andVenezuela,savannasoccupysome2.5millionsquarekilometers,anareaaboutonequarterthesizeofCanada.Animalsfromtheneighboringbiomeskindofspillintothissavanna.TheLlanosoftheOrinocobasinofVenezuelaandColumbiaisfloodedannuallybytheOrinocoRiver.Plantshaveadaptedtogrowingforlongperiodsinstandingwater.Thecapybaraandmarshdeerhaveadaptedthemselvestoasemiaquaticlife.

    Brazil'scerradoisanopenwoodlandofshorttwistedtrees.Thediversityofanimalsisverygreathere,withseveralplantsandanimalsthatdon'texistanywhereelseonearth.

    ThereisalsoasavannainnorthernAustralia.EucalyptustreestaketheplaceofacaciasintheAustraliansavanna.TherearemanyspeciesofkangaroosinthissavannabutnottoomuchdiversityofdifferentanimalsPlantsofthesavannasarehighlyspecializedtogrowinthisenvironmentoflongperiodsofdrought.Theyhavelongtaprootsthatcanreachthedeepwatertable,thickbarktoresistannualfires,trunksthatcanstorewater,andleavesthatdropofduringthewintertoconservewater.Thegrasseshaveadaptationsthatdiscourageanimalsfromgrazingonthemsomegrassesaretoosharporbittertastingforsomeanimals,butnotothers,toeat.Thesidebenefitofthisisthateveryspeciesofanimalhassomethingtoeat.Differentspecieswillalsoeatdifferentpartsofthegrass.Manygrassesgrowfromthebottomup,sothatthegrowthtissuedoesn'tgetdamagedbygrazers.Manyplantsofthesavannaalsohavestorageorganslikebulbsandcormsformakingitthoughthedryseason.

    Mostoftheanimalsonthesavannahavelonglegsorwingstobeabletogoonlongmigrations.Manyburrowundergroundtoavoidtheheatorraisetheiryoung.Thesavannaisaperfectplaceforbirdsofpreylikehawksandbuzzards.Thewide,openplainprovidesthemwithaclearviewoftheirprey,hotairupdraftskeepthemsoaring,andthereistheoccasionaltreetorestonornestin.Animalsdon'tsweattolosebodyheat,sotheyloseitthroughpantingorthroughlargeareasofexposedskin,orears,likethoseoftheelephant.

    Thesavannahasalargerangeofhighlyspecializedplantsandanimals.Theyalldependontheeachothertokeeptheenvironmentinbalance.Thereareover40differentspeciesofhoofedmammalsthatliveonthesavannasofAfrica.Upto16differentspeciesofbrowsers(thosewhoeatleavesoftrees)andgrazerscancoexistinonearea.Theydothisbyhavingtheirownfoodpreferences,browsing/grazingatdifferentheights,timeofdayoryeartouseagivenarea,anddifferentplacestogoduringthedryseason.

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    Thesedifferentherbivoresprovideawiderangeoffoodforcarnivores,likelions,leopards,cheetahs,jackalsandhyenas.Eachspecieshasitsownpreference,makingitpossibletolivesidebysideandnotbeincompetitionforfood.

    InmanypartsofthesavannasofAfricapeoplehavestartedusingittograzetheircattleandgoats.Theydon'tmovearoundandsoonthegrassesarecompletelyeatenup.Withnovegetation,thesavannaturnsintoadesert.HugeareasofsavannaarelosttotheSaharadeserteveryyearbecauseofovergrazingandfarming.

    Alpineecosystem

    Cold,snowy,windy.Whenyouhearthosewordstheymakeyouthinkofmountains.TheAlpinebiomeislikewinteristopeopleinNewEnglandsnow,highwinds,ice,allthetypicalwinterthings.InLatinthewordfor'highmountain'is'alpes'.Thatiswheretoday'swordalpinecomesfrom.Alpinebiomesarefoundinthemountainregionsallaroundtheworld.Theyareusuallyatanaltitudeofabout10,000feetormore.TheAlpinebiomeliesjustbelowthesnowlineofamountain.Asyougoupamountain,youwilltravelthroughmanybiomes.IntheNorthAmericanRockyMountainsyoubegininadesertbiome.Asyouclimbyougothroughadeciduousforestbiome,grasslandbiome,steppebiome,andtaigabiomebeforeyoureachthecoldAlpinebiome.

    Inthesummeraveragetemperaturesrangefrom10to15C.Inthewinterthetemperaturesarebelowfreezing.ThewinterseasoncanlastfromOctobertoMay.ThesummerseasonmaylastfromJunetoSeptember.ThetemperaturesintheAlpinebiomecanalsochangefromwarmtofreezinginoneday.

    BecausethesevereclimateoftheAlpinebiome,plantsandanimalshavedevelopedadaptationstothoseconditions.Thereareonlyabout200speciesofAlpineplants.AthighaltitudesthereisverylittleCO2,whichplantsneedtocarryonphotosynthesis.Becauseofthecoldandwind,mostplantsaresmallperennialgroundcoverplantswhichgrowandreproduceslowly.Theyprotectthemselvesfromthecoldandwindbyhuggingtheground.Tallerplantsortreeswouldsoongetblownoverandfreeze.Whenplantsdietheydon'tdecomposeveryquicklybecauseofthecold.Thismakesforpoorsoilconditions.MostAlpineplantscangrowinsandyandrockysoil.PlantshavealsoadaptedtothedryconditionsoftheAlpinebiome.PlantbooksandcatalogswarnyouaboutoverwateringAlpineplants.

    Alpineanimalshavetodealwithtwotypesofproblems:thecoldandtoomuchhighUVwavelengths.ThisisbecausethereislessatmospheretofilterUVraysfromthesun.ThereareonlywarmbloodedanimalsintheAlpinebiome,althoughthereareinsects.Alpineanimalsadapttothecoldbyhibernating,migratingtolower,warmerareas,orinsulatingtheirbodieswithlayersoffat.Animalswillalsotendtohaveshorterlegs,tails,andears,inordertoreduceheatloss.Alpineanimalsalsohavelargerlungs,morebloodcellsandhemoglobinbecauseoftheincreaseofpressureandlackofoxygenathigheraltitudes.Thisisalsotrueforpeoplewhohavelivedonmountainsforalongtime,liketheIndiansoftheAndesMountainsinSouthAmericaandtheSherpasoftheHimalayasinAsia.

    chaparralEcosystem

    ThechaparralbiomeisfoundinalittlebitofmostofthecontinentsthewestcoastoftheUnitedStates,thewestcoastofSouthAmerica,theCapeTownareaofSouthAfrica,thewesterntipofAustraliaandthecoastalareasoftheMediterranean.

    Layoftheland:Thechaparralbiomehasmanydifferenttypesofterrain.Someexamplesareflatplains,rockyhillsandmountainslopes.Itissometimesusedinmoviesforthe"WildWest".

    Chaparralischaracterizedasbeingveryhotanddry.Asforthetemperature,thewinterisverymildandisusuallyabout10C.Thenthereisthesummer.Itissohotanddryat40Cthatfiresanddroughtsareverycommon.

    Fortunately,theplantsandanimalsareadaptedtotheseconditions.Mostoftheplantshavesmall,hardleaveswhichholdmoisture.Someoftheseplantsarepoisonoak,scruboak,YuccaWipleandothershrubs,treesandcacti.

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    #8

    Theanimalsareallmainlygrasslandanddeserttypesadaptedtohot,dryweather.Afewexamples:coyotes,jackrabbits,muledeer,alligatorlizards,hornedtoads,prayingmantis,honeybeeandladybugs.So,ifyouevergosomewherethatislikechaparral,makesuretobringsomesunscreenandlotsofwater!

    LasteditedbyXericFriday,May15,2009at08:31PM.

    Sunday,April19,2009

    AFRMS37thCommon

    JoinDate:Mar2006Posts:1,514Thanks:1,053Thanked1,670Timesin871Posts

    ZoologyNotes

    PlacentalStructureandClassification

    Placenta

    thevascular(suppliedwithbloodvessels)organinmostmammalsthatunitesthefetustotheuterusofthemother.Itmediatesthemetabolicexchangesofthedevelopingindividualthroughanintimateassociationofembryonictissuesandofcertainuterinetissues,servingthefunctionsofnutrition,respiration,andexcretion

    Theplacentasofalleutherian(placental)mammalsprovidecommonstructuralandfunctionalfeatures,buttherearestrikingdifferencesamongspeciesingrossandmicroscopicstructureoftheplacenta.Twocharacteristicsareparticularlydivergentandformbasesforclassificationofplacentaltypes:

    1.Thegrossshapeoftheplacentaandthedistributionofcontactsitesbetweenfetalmembranesandendometrium.

    2.Thenumberoflayersoftissuebetweenmaternalandfetalvascularsystems.

    Differencesinthesetwopropertiesallowclassificationofplacentasintoseveralfundamentaltypes.

    ClassificationBasedonPlacentalShapeandContactPoints

    Examinationofplacentaefromdifferentspeciesrevealsstrikingdifferencesintheirshapeandtheareaofcontactbetweenfetalandmaternaltissue:

    Diffuse:Almosttheentiresurfaceoftheallantochorionisinvolvedinformationoftheplacenta.Seeninhorsesandpigs.Cotyledonary:Multiple,discreteareasofattachmentcalledcotyledonsareformedbyinteractionofpatchesofallantochorionwithendometrium.Thefetalportionsofthistypeofplacentaarecalledcotyledons,thematernalcontactsites(caruncles),andthecotyledoncarunclecomplexaplacentome.Thistypeofplacentationisobservedinruminants.Zonary:Theplacentatakestheformofacompleteorincompletebandoftissuesurroundingthefetus.Seenincarnivoreslikedogsandcats,seals,bears,andelephants.Discoid:Asingleplacentaisformedandisdiscoidinshape.Seeninprimatesandrodents.

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    ClassificationBasedonLayersBetweenFetalandMaternalBlood

    Justpriortoformationoftheplacenta,thereareatotalofsixlayersoftissueseparatingmaternalandfetalblood.Therearethreelayersoffetalextraembryonicmembranesinthechorioallantoicplacentaofallmammals,allofwhicharecomponentsofthematureplacenta:

    1.Endotheliumliningallantoiccapillaries2.Connectivetissueintheformofchorioallantoicmesoderm3.Chorionicepithelium,theoutermostlayeroffetalmembranesderivedfromtrophoblast

    Therearealsothreelayersonthematernalside,butthenumberoftheselayerswhichareretainedthatis,notdestroyedintheprocessofplacentationvariesgreatlyamongspecies.Thethreepotentialmaternallayersinaplacentaare:

    1.Endotheliumliningendometrialbloodvessels2.Connectivetissueoftheendometrium3.Endometrialepithelialcells

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    #9

    Inhumans,fetalchorionicepitheliumisbathedinmaternalbloodbecausechorionicvillihaveerodedthroughmaternalendothelium.Incontrast,thechorionicepitheliumofhorseandpigfetusesremainsseparatedfrommaternalbloodby3layersoftissue.Onemightthusbetemptedtoconsiderthatexchangeacrosstheequineplacentaismuchlessefficientthatacrossthehumanplacenta.Inasensethisistrue,butotherfeaturesofplacentalstructuremakeupfortheextralayersinthediffusionbarrierithasbeenwellstatedthat"Thenewbornfoalprovidesastrongtestimonialtotheefficiencyoftheepitheliochorialplacenta."

    SummaryofSpeciesDifferencesinPlacentalArchitecture

    Theplacentalmammalshaveevolvedavarietyofplacentaltypeswhichcanbebroadlyclassifiedusingthenomenclaturedescribedabove.Notallcombinationsofthoseclassificationschemesareseenorarelikelytoeverbeseenforinstance,nomammalisknowntohaveadiffuse,endotheliochorial,orahemoendothelialplacenta.Placentaltypesfor"familiar"mammalsaresummarizedbelow,withsupplementalinformationprovidedforavarietyof"nonfamiliar"species.

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    Sunday,April19,2009

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    Mammals

    Mammals

    Thereareapproximately4,260differentmammalianspeciesthathavebeendiscoveredtodate,althoughthisfigurevariesbecausenotallscientistsagreethatcertainorganismsareadistinctspecies.Inaddition,newspeciesarealwaysbeingdiscovered,thereforethisfigureofhowmanydifferentmammalsexistisalwayschanging.Mammalsareallwarmblooded,andallmammalsarevertebrates(meaningtheyhavevertebrae,formingaspine),buttherearealsootheranimals,likebirds,thathavethesecharacteristics,sothereareadditionaltraitsthatsetmammalsapart.

    CharacteristicsofMammals

    Mammalshavesixkeycharacteristicsthatcanbeseenineachandeverymammal,anditsthesetraitsthatsetmammalsapartfromothertypesofcreatures:1.Mammalsproducemilktofeedtheiryoung.Femalemammalspossessamodifiedsweatglandamammaryglandthatisactivatedbyhormonalchangesthatoccurwithpregnancy.Infact,thistraitiswhatinspiredthetermmammal,aderivationofmammary.2.Mammalsallhaveonesinglebonecomprisingtheirlowerjaw.Inallotheranimals,morethanonebonecomprisesthejaw.3.Allmammalshavethreetinybonesinthemiddleportionoftheear.4.Allmammalshaveadiaphragm.Themammal'sdiaphragmisathinmuscularwallthatseparatestheupperandlowerportionsofthetorso.5.Allmammalshavefurorhair.Hairorfurisacharacteristicthat'sonlyseeninmammals.Allmammalsdevelopfurorhairatsomepointduringtheirdevelopment,thoughnotallkeeptheirfurorhairthroughouttheirlifespan.6.Mammalshaveauniqueheart.Theheartofamammalisuniqueinthatithasoneprimaryarteryleavingtheheartbendingtotheleft,whereasotheranimalseitherhavemultiplearteriesintheheartortheheart'smainarterybendsinadifferentdirection.

    CategoriesofMammals

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    #10

    Withintheclassofanimalsconsideredmammals,therearethreecategories:eutheria,metatheriaandprototheria.Thethreecategoriesofmammalscanbedescribedasfollows:1.EutheriaEutheriaaremammalspossessingaplacenta,likeahumanordog.2.MetatheriaMetatheriaarealsoknownasmarsupialsorpouchbearingmammalslikethekangaroo.3.PrototheriaPrototheriaarealsoknownasmonotremesoregglayingmammalsliketheduckbillplatypus.

    ExclusiveTraitsofMammals

    Inaddition,thereareafewcharacteristicsthatareexclusivetomammals,meaningonlyanimalshavethesetraits.But,ineachcase,therearesomemammalsthatdon'thavethesetraits,whichiswhythey'redifferentfromthecharacteristicsofmammals(themammalcharacteristicsareseenineachandeverymammal).Thevastmajorityoffemalemammalshaveaplacenta,usedtoprotectandnourishtheoffspringpriortobirth.Marsupialsandmonotremesdonothaveaplacenta.Intheirlifetime,amammalwillnothavemorethantwosetsofteeth.Typically,mammalsgrowonesetofteethasjuveniles,andthenanewpermanentsetgrowsinastheynearadulthood.Amammaliswarmblooded,meaningithastheabilitytogenerateitsownbodyheatandmaintainasteadybodytemperature,despiteambienttemperaturechanges.Mammalsalsohaveaseparationbetweentheirmouthandnasalcavity.Otheranimals,likereptilesdonothaveanupperpalatethisallowsthenasalcavitytoremainopenregardlessofwhetherthereissomethinginsidethemouth.

    MultituberculatesAnExtinctCategoryofMammals

    Inadditiontothethreecategoriesofmammalseutheria,metatheriaandprototheriatherewasonceafourthmammalcategorythatisnowcompletelyextinct.MultituberculatesareacategoryofmammalthataroseduringthelateJurassicperiod160millionyearsagoandtheysurvivedupuntilabout35millionyearsago.Multituberculateshavenolivingdescendantstoday,butfossilrecordsindicatethattheyweresimilartomodernrodents.Multituberculateswerenamedfortheirteeth.Thesemammalshadonepairofincisorsonthelowerjawandtheirmolarshadnumerouscuspsformingnumerousrowsofteeth.Thesemammalsalsolackedcanineteethontheupperjaw,likemanyrodentsoftoday.

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    Birds

    Birds,anIntroduction

    Birdsarewarmbloodedvertebrates,withforelimbsmodifiedtowings,andskinscoveredwithfeathers.Vertebratesarecharacterisedbyhavingaspinalcolumnandaskull.Warmbloodedorhomoiothermic(constanttemperature)meansthattheirbodytemperatureiskeptmoreorlessconstantandabovethatoftheirsurroundings.Typically,theforelimbsaswingsgivebirdsthepowerofflightalthoughtherearesomeflightlessbirds.Insomecases(e.g.penguinsandpuffins)thewingsareusedforswimmingunderwater.Allbirdsreproducebylayingeggswhicharefertilisedinternallybeforelaying.Theskullandlowerjawareextendedforwardintomandibleswhichmakeabeak.Thebird'slegsandtoesarecoveredwithoverlappingscales.Birdspossessathird,transparenteyelid,thenictitatingmembrane,whichcanmoveacrosstheeye.

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    Feathers

    Thefeathersarethesingleexternalfeaturethatdistinguishbirdsfromothervertebrates.Thefeathersareproducedfromtheskinwhichislooseanddry,withoutsweatglands,andtheyformaninsulatinglayerroundthebird'sbody,helpingtokeepitstemperatureconstant,andrepellingwater.Thewingsarespeciallydevelopedforflight,havingalargesurfaceareaandverylittleweight.

    Thebarbulesofthefeathersinterlockinsuchawaythatshouldafeatherbedamagedinflight,preeningwiththebeakwillreformitperfectly.

    Thefeatherquillshaveattachedtothemmuscleswhichcanaltertheanglesofthefeathersforexample,whenabirdfluffsitsfeathersoutincoldweather.Theyalsohaveanervesupplywhich,whenthefeathersaretouched,isstimulatedinasimilarwaytoacat'swhiskers.

    Thedownfeathersarefluffy,trappingalayerofairclosetothebody.Theflightfeathersandcovertsarebroadandflatandofferresistancetothepassageofair.

    Theshapeofthebirdandthelayofitsfeathersmakeitstreamlinedinflight.

    Featureswhichadaptthebirdforflying

    1.Theforelimbsarewingswithalargesurfaceareaprovidedbyfeathers.However,ratherthanbeinganadaptationtoflighttheyareessentialforflighttotakeplace.

    2.Largepectoralmusclesfordepressingthewings.Theymayaccountforasmuchasonefifthofthebodyweightinsomebirds.

    3.Adeep,keellikeextensionfromthesternum(breastbone)providesfortheattachmentofthepectoralmuscles.Welldevelopedcoracoidbonestransmittheliftofthewingstothebody.

    4.Arigidskeletongivingafirmframeworkforattachmentofmusclesconcernedwithflyingmovements.Manyoftheboneswhichcanmoveinmammalsarefusedtogetherinbirdsforexample,thevertebraeofthespinalcolumninthebodyregion.

    5.Hollowbones,whichreducethebird'sweight.

    Locomotion

    Theflightofabirdcanbedividedintoflapping,andglidingorsoaring,differentspeciesofbirdsusingthetwotypestovaryingextents.Inflappingflightthepectoralismajormusclecontracts,pullingtheforelimbdown.Theresistanceoftheairtothewingproducesanupwardreactiononthewing.Thisforceistransmittedthroughthecoracoidbonestothesternumandsoactsthroughthebird'scentreofgravity,liftingitasawhole.

    Inadditiontothelift,forwardmomentumisprovidedbytheslicingactionofthewing,particularlynearthetip.Inthedownstroketheleadingedgeisbelowthetrailingedgesothattheairisthrustbackwardsandthebirdmovesforward.Thesecondaryfeathersprovidemuchoftheliftingforceandtheprimariesmostoftheforwardcomponent.

    Thebastardwing(agroupoffeathersattachedtothefirstdigit)maybeimportantduringtakeoffforgivingaforwardthrust.Duringflightitmayfunctionasaslotmaintainingasmoothflowofairoverthewingsurface.

    Theupstrokeofthewingismuchmorerapidthanthedownstroke.Thepectoralisminormusclecontractsandraisesthewing,sinceitstendonpassesoveragrooveinthecoracoidtotheuppersideofthehumerus.Oftenthearmissimplyrotatedslightlysothattheleadingedgeishigherthanthetrailingedgeandtherushofairliftsthewing.Thewingisbentatthewristduringtheupstrokethusreducingtheresistance.Inaddition,thewayinwhichtheprimaryandsecondaryfeathersoverlapproducesmaximumresistanceduringthedownstrokeandminimumresistanceontheupstroke.

    Inglidingflightthewingsareoutspreadandusedasaerofoils,thebirdslidingdowna'cushion'ofair,losingheightandgainingforwardmomentum.Sometimesupwardthermalcurrentsorintermittentgustsofwindmaybeusedtogainheightwithoutwingmovementsinseagullsandbuzzardsforexample.

    Generally,thefastflyingbirdshaveasmallwingareaandalargespan,withspeciallywell

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    Generally,thefastflyingbirdshaveasmallwingareaandalargespan,withspeciallywelldevelopedprimaries,whiletheslowerbirdshaveshorter,widerwingswithwelldevelopedsecondaries.

    Estimatesofspeedvaryfrom160km/hinswiftsto60km/hinracingpigeons.Thetailfeathershelptostabilizethebirdinflightandareparticularlyimportantinbrakingandlanding.

    Inwalking,thepostureofthebirdbringsthecentreofgravityofthebirdbelowthejointofthefemurandpelvis.

    Reproduction

    Thedetailedpatternofreproductionandparentalcarevarieswidelyindifferentspeciesbut,ingeneral,itfollowsthecourseoutlinedbelow.

    Pairing.Asequenceofbehaviouralactivities,e.g.courtshipdisplay,leadstopairformationamaleandfemalebirdpairingatleastforthedurationofthebreedingseason.

    Nestbuilding.Oneofthepairorbothbirdsconstructanestwhichmaybeanelaboratestructurewovenfromgrass,leaves,feathers,etc.,orlittlemorethanahollowscrapedintheground.

    Mating.Furtherdisplayleadstomating.Themalemountsthefemale,applieshisreproductiveopeningstohersandpassesspermintoheroviduct,thusenablingtheeggstobefertilizedinternally.

    Egglaying.Thefertilizedeggisenclosedinalayerofalbumenandashellduringitspassagedowntheoviductandisfinallylaidinthenest.Usually,oneeggislaideachdayandincubationdoesnotbeginuntilthefullclutchhasbeenlaid.

    Incubation.Thefemalebirdisusuallyresponsibleforincubation,keepingtheeggsatatemperatureapproximatingtoherownbycoveringthemwithherbodyandpressingthemagainstherbroodingpatches,i.e.areasdevoidoffeatherswhichallowdirectcontactbetweentheskinandtheeggshell.Incubationalsoreducesevaporationofwaterfromtheshell.Atthistemperature,theeggsdevelopandhatchinaweekortwo.

    Development.Thelivingcellsintheeggdividetomakethetissuesandorgansoftheyoungbirds.Theyolkprovidesthefoodforthisandthealbumenisasourceofbothfoodandwater.Theeggshellandshellmembranesarepermeable,andoxygendiffusesintotheairspace,beingabsorbedbypartofthenetworkofcapillarieswhichspreadoutovertheyolkandoveraspecialsac,theallantois,whichhasbecomeattachedtotheairspace.Thebloodcarriestheoxygentotheembryo.Carbondioxideiseliminatedbythereverseprocessthroughtheeggshell.Whenthechicksarefullydeveloped,theybreakoutoftheshellbyusingtheirbeaks.

    Parentalcare.Thechicksoflarge,groundnestingbirds,e.g.pheasant,arecoveredwithdownyfeathersandcanrunaboutsoonafterhatching.Theypeckatobjectsonthegroundandsoonlearntodiscriminatematerialsuitableforfood.Theystayclosetothehen,respondingtohercallsbytakingcoverorseekingheroutaccordingtothecircumstances.

    Inmostotherspecies,thechickshatchwithfewornofeathers,helplessandwithclosedeyelids.Havingnofeathers,theyareverysusceptibletoheatlossanddesiccation,andtheparentsbroodthem,coveringthenestwiththebodyandwings,soreducingevaporationandtemperaturefluctuations.Bothparentswillcollectsuitablefood,oftenworms,caterpillars,insectsandothermaterialsequallyrichinprotein.Thesoundorsightoftheparentsapproachingthenestcausesthenestlingstostretchtheirnecksandgapetheirbeaks.Thebrightorangecolourinsidethebeaksinducestheparenttothrustthefooditiscarryingintotheopenbeaks.

    Afteraweekortwo,theyoungbirdsbegintoclimboutofthenestandsitinthebushortreebuttheparentsstillfindandfeedthem.Whentheprimaryandsecondaryfeathershavedeveloped,thefledglingsbeginshortpracticeflights.Thisisoneofthemostdangerousperiodsoftheirlivessincetheycanfeedthemselvestoonlyalimitedextentandcannotescapefrompredatorssuchascatsandhawks.Someestimatessuggestthatonly25percentoftheeggslaidinopennestsofthiskindreachthestageoffullyindependentbirds.

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    ofthiskindreachthestageoffullyindependentbirds.

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