英语听力英语高级听力材料Wild AfricaDesertsWord下载.docx
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Beetles,manydifferentspecieshavefoundwaystoharvestthisbounty.Alongwithtermitesandlizards,they'
rethefoundationsforadelicatechainoflifeintheNamib.
Inthisbarrenseaofsand,it'
sharderforlargeranimalstofindenoughtoeat.You'
vegottobearealspecialist,liketheNamibsandsnake.Bysidewinding,itcanswimitswayupthedunes.Butinsuchanopenarena,ambushistricky,it'
sspeedthatcounts.Thewedge-snoutedlizardcanaffordtobeblase.Ithasasecretweapon,rocketpropulsion.Thenit'
sunderthesandasfastasyoucan,thebestplacetoescapepredatorsandthesun.
HereintheNamib,shelterissparse.Whatlittlethereis,isfiercelyprotected.ColoniesofduneantsmonopoliesthetoughNamibgrasses.Thoughaggressivetomostinvaders,theantsdotoleratethepresenceofsmallsap-suckingbugswhichtheygettomilkforprecioussugarywater.Intheirgrassyhome,theantsareshadedfromtheworstofthesun.Butoutonthesurfaceofthesand,thetemperaturecanreachablistering60Celsius.
Spoorspidershaveanextraordinarysurvivalstrategy.Withnowheretohangtheirwebs,theyspintheirsilkontheground,meshingsandgrainstogether.Theresult:
aminiblanketwhichservesasasunscreen.Butthesesandyblanketsdomorethanshelter.Theyarebeautifullycamouflagedstickytraps.
Duneantsgetmostofthefoodtheyneedontheirdoorstep.Buttosupplementtheirdiettheymustalsoventureoutontothesand.Theirlonglegsliftthemabovethebakinggroundtowherethetemperatureisslightlycooler.Buttheymuststilltreadcarefully,it'
saminefieldoutthere.
Pinningtheantstothehotsandsurface,thespidersfirstcookthemtodeathbeforedraggingthemunder.
IntheNamib,eventhetoughestanimalsstrugglewiththeheat.Gemsboktrektothecrestsofthehighestdunestoseekreliefinthebreeze.
Withnocloudcover,solarradiationblastingthedesertisintense.Themid-daysandissohot.It'
slikeabedofburningcoals.TheNamibquickstep.Overmillionsofyears,youlearntokeepyourclawscool.Pushedbythewind,thedunesavalanche.TheNamib'
sresidentscan'
tfightthetide.
Thoughthedunesareunstable,theyprovideahomeforaremarkablecreature.Thetrapdoorspideronlybuildsitsnestonthetopofthesteepestdunes.It'
slearnedtodothisbecauseithasaveryaggressiveenemy,awasp,whichrelentlesslyscoursthesand.
Thoughitseyesightispoor,thewasphasverysensitivehairsonitslegswhichcanpickuptheslightestscentofaspider.Whenitfindsanest,thewaspquicklyworksouthowdeeptheburrowis.Ifit'
sshallow,thewaspstartsdiggingforuptotwohours.It'
shardworkagainsttheslippingsand.
Withthespiderexposed,it'
snowabattlebetweenthewasp'
sparalyzingstingandthespider'
sjaws.Butthewasphasquickreflexes.Cornered,thespidernowplaysitstrumpcard.Hurlingitselfdownthedune,itflipsintoawheel.Travelingatover40turnsasecond,itmakesadizzydashforfreedom.Safe,atlast.
Backupthedune,thewaspisleftstanding,chasingthescentofitsvanishedmeal.
Instincthonedovertime,governsmuchofthelifeintheNamib.Butsomecreaturesalsohavetolearnhowtoconquerthesesands,usingknowledgepasseddownovergenerations.
Africanelephantsaresoresourceful,theycansurviveevenhereintheheartofthedesert.
Elephantshaveremarkablepowersofmemory.Thoughthisdesertismorethan2millionsquarekilometersinsize,100orsoelephantsitsupportsknowpreciselywheretofindenoughtoeatanddrink.Ittakesalotoffood,upto300kilosadaytofeedtheworld'
slargestlandanimal.Andallofthat-fromadesert.
Butthere'
soneplanthere,theNara,whoserootsdrawwaterfromdeepunderground.Eachyearitproducesabumpercropofmelons.Elephantsjustlovethem.
Eachmelonisavaluablepackageofmoistureandseeds.Theplantalsobenefitsfromthisplunderasitsseedsmaybecarriedforfiftykilometersintheelephant'
sstomachbeforebeingdroppedinapileoffertilizingdung.
ButtheNaraneedsmorethanapassingtradewithelephantstospreaditsseeds.Underthecoverofdarkness,thenutritiousmelonsalsopullinthelocals,likeCapeporcupines.Porcupinesmaywanderuptofifteenkilometersanightinsearchofripemelons.Theyrelyonasharpsenseofsmell.
Naramelonshaveatoughoutershell,buttheporcupines'
largeincisorsmakeshortworkofthem.Likeelephants,porcupineshelptheNaratospreaditsseeds.Byopeningupfruits,theyalsocreateopportunitiesforotherdunecreatures.
Hairy-footedgerbilsarehotontheirheels.Inthecoolofthedesertnight,theselittlerodentsburnupenergyquickly,andsomustgatherfoodfast.Thoughplentiful,theNaraseedstakesomeplucking.Thegerbilsprovisionforleanertimesahead,buttheymustalsokeepalert.
CavefoxespatroltheNarabushes,lookingforgerbils.Surprisingly,thefoxesarealsopartialtothethirst-quenchingmelons.Butthereisagreatmysteryhere.ThisisthemostextremeAfricanenvironment;
itmaynotrainfortenyearsatastretch.SohowdoestheNamibsupportsomuchlife?
Oncertainnights,thesecretisrevealed.Warm,dampairmovinginfromthemid-Atlanticistransformedtofogasitcrossesthecoldcoastalcurrent.
Avastblanketofmoisturesteadilyrollsacrossthedesert.
ThisveilofmististhesavinggraceoftheNamib.Justafewpreciousdropsbutenoughtoallowlifetoflourish.Atinybitofmoisture,atinybitoffoodandtensofmillionsofyearsofevolutionarethesecretstosuccessinthisharshestofAfricandeserts.
WhereelsebuttheNamibwouldaningeniouslittlebeetlestaggerupthehighestdunesoncoldmornings,putitsbacktobreeze,andthenstandonitsheadtocollectalife-givingdrink?
ImpressivesanddunesdominatetheNamib,buttothesouthandeastisaverydifferentkindofdesert,anexpanseofrockyscrubknownasthekaroo.
ThisdesertisasoldastheNamib,buthereitismainlyrain,notfogthatdriveslife.Inthekaroo,upto30centimetersofrainmayfallduringwinterandthisextrasprinkleofmoisturemakestheworldofdifference.
Inspring,thedesertundergoesaremarkabletransformation.
Forjustafewweeksayear,theflowersofover3,000differentplantspeciesturnthisdesertintotheGardenofAfrica.
Thisdazzlingvarietyofcolorhasevolvedovertimeforaveryspecialpurpose--forplantstoseducetheirinsectpollinators.
Someextraordinaryrelationshipshavebeenforged.ThebrightpurpleblossomsofLapeirousiaaredesignedpurelytoattracttheflywiththelongesttongueinAfrica.Astheflyprobesforasipofnectarinthelongfloraltubes,pollenisdabbedontoitsforehead.Asmartdesign,butonawindyday,it'
snotsoeasytohitthetarget.
Diasciaflowersusenotnectarbutnutritiousoilssecretedbyglandsatthetipsoftheirfloraltubestotemptpollinators.Flowerandbee,inthiscase,aperfectfitastheinsectdipsitstoesforoil.
Ignitedbytherain,thefloweringoftheKarootouchesthelivesofallitsinhabitants.Brandt'
swhistlingratsarequicktoharvesttheblossomsaroundtheirburrows.
Thesedesertratstimetheirbreedingtothebirthoffreshfood,butwithsnakesaround,motherscan'
triskleavingtheiryoungstersathome.Clingingtohernipples,they'
recarriedalong,asortofmealsonwheels.
Withinamonth,thespringbloomsarefinished.Theplantsnowsettheirseeds,takingadvantageofthewarmsummerwindswhichsweepthedesert.
Forawhile,thekaroojustglows.
Buttroubleisstiring.Triggeredbytherains,anall-devouringarmy--locusts.
Millionsemergefromeggsburiedinthesand,gatheringintocolumnswhichmaystretchfortenkilometers.Atthisstage,theycan'
tfly,onlyhop,butitdoesn'
thindertheirprogress.Thesesweepinghordesdevastateanyfreshgrowthintheirpath.
Afterfiveweeksofsteadymunching,theinfantrybecomesairborne.Thesebreedingswarmscancoverupto80kilometersaday,butonlywhilethefoodandmoisturelast.
SohowdoyoudefineadesertinAfrica?
Theyareplaceswherelessthan50centimetersofrainfallsayear.Neighbouringthekarooisadesertwhichgetsthemaximum,inbrief,butintensesummermonsoons.
It’sthewettestofallAfricandeserts,thegreatKalahari.
ThesandsoftheKalaharicovermoreofsouthernAfricathananyotherdesert.Butthehigherrainfallheregivesitaverydistinctiveappearance.Morelikeasavanna,itssandyridgescarpetedwithgrassesandascatteringoftrees.Inthewetseason,theKalaharisandsareloosenedbytherain,makingthemeasiertoexcavate.
Damaramole-ratswhospendtheirlivesundergroundarenowattheirmostactive,huntingforrootsandbulbs.Butdiggingtakesonethousa