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Sunday,September23,2007

AFRMS37thCommon

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

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.



#2

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

Geneticdriftinpopulations

Driftcanhaveprofoundandoftenbizarreeffectsontheevolutionaryhistoryofapopulation.Theseeffectsmaybeatoddswiththesurvivalofthepopulation.

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

Similarly,migratingpopulationsmayseeafoundereffect,whereafewindividualswithararealleleintheoriginatinggenerationcanproduceapopulationthathasallelefrequenciesthatseemtobeatoddswithnaturalselection.Founder'seffectsaresometimesheldtoberesponsibleforhighfrequenciesofsomegeneticdiseases.

LasteditedbyLastIslandFriday,May15,2009at08:18PM.

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Sunday,September23,2007

AFRMS37thCommon


zoologynitrogencycle

TheNitrogenCycle

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



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



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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LasteditedbyLastIslandFriday,May15,2009at08:14PM.

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#3

djdon(Friday,December31,2010)

Wednesday,October03,2007

AFRMS37thCommon


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



#4

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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Friday,October05,2007

AFRMS37thCommon


zoologyEcosystem

WhatisaBiome?

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

Deciduousforests



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,



#5

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

LasteditedbyXericFriday,May15,2009at08:27PM.


AFRMS37thCommon


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.




#6

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AFRMS37thCommon


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.



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



#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.


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AFRMS37thCommon


Savanna,Alpine,chaparralecosystem



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.



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.



#8

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


Sunday,April19,2009

AFRMS37thCommon


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.



ClassificationBasedonLayersBetweenFetalandMaternalBlood

Justpriortoformationoftheplacenta,thereareatotalofsixlayersoftissueseparatingmaternalandfetalblood.Therearethreelayersoffetalextraembryonicmembranesinthechorioallantoicplacentaofallmammals,allofwhicharecomponentsofthematureplacenta:

1.Endotheliumliningallantoiccapillaries2.Connectivetissueintheformofchorioallantoicmesoderm3.Chorionicepithelium,theoutermostlayeroffetalmembranesderivedfromtrophoblast

Therearealsothreelayersonthematernalside,butthenumberoftheselayerswhichareretainedthatis,notdestroyedintheprocessofplacentationvariesgreatlyamongspecies.Thethreepotentialmaternallayersinaplacentaare:

1.Endotheliumliningendometrialbloodvessels2.Connectivetissueoftheendometrium3.Endometrialepithelialcells



#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

AFRMS37thCommon


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



#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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Monday,April20,2009

AFRMS37thCommon


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.



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



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.



ofthiskindreachthestageoffullyindependentbirds.

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