Chapter 4TemperatureRelations.docx

Chapter 4TemperatureRelations.docx

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Chapter4TemperatureRelations

Chapter4TemperatureRelations

PeterKevanhadcometoEllesmereIsland,whichliesatabout82°NlatitudeintheNorthwestTerritoriesofCanada,tostudysun-trackingbehaviorbyarcticflowers.Itwassummer,therewaslittlewind,andthesunstayedabovethehorizon24hourseachday.Asthesun'spositioninthearcticskychanged,oneofthecommontundraflowers,Dryasintegrifolia（fig.4.1）,likethesunflowersoflowerlatitudes,followed.

Kevanfoundthatthesun-trackingbehaviorofDryasincreasedthetemperatureofitsflowers.Thoughtheairtemperaturehoveredaround15℃,thetemperatureoftheDryasflowerswasnearly25℃.Kevandiscoveredthattheflowersactlikesmallsolarreflectors;theirparabolicshapereflectsandconcentratessolarenergyonthereproductivestructures.Healsoobservedthatmanyspeciesofsmallinsects,attractedbytheirwarmth,baskedinthesun-trackingDryasflowers,elevatingtheirbodytemperaturesasaconsequence（fig.4.1）.Dryasdependsontheseinsectstopollinateitsflowers.

FIGURE4.1Sun-trackingbehaviorofDryasintegrifolia.

HowdoesDryasanditsinsectvisitorsbenefitfromtheirbaskingbehaviors?

Howdoescloudcoveraffectthetemperatureandsun-trackingbehaviorofDryasflowers?

ThesearethekindsofquestionsaddressedbyKevan（1975）andotherecologistswhostudytheecologyoftemperaturerelations,oneofthemostfundamentalaspectsofecology.Intheirquestforanswerstoquestionslikethese,ecologistslearnhowtheworldworks.

Thethermometerwasoneofthefirstquantitativeinstrumentstoappearinthescientifictoolkit,andwehavebeenmeasuringandreportingtemperatureseversince.Humanconcernfortemperatureshowsitselfeverywhere.Localtelevisionreviewsthehighandlowtemperaturesoftheprecedingdayandforecaststemperaturesforthecomingday.Dailynewspapersreporttemperaturesfromnearlyeverycorneroftheglobe.Iftwopeoplefromdifferentregionsmeet,thefirstquestionstheyaskconcerntheweather:

Arethesummersveryhot?

Arethewinterscold?

Wewearourenduranceofextremetemperatureslikebadgesofheroism;yettodaywelistenapprehensivelytotheforecastofasmalltemperaturechange--theprospectofglobalwarming.

WhyisHomosapienssoconcernedwithtemperature?

Forusandallotherspecies,theimpactofextremetemperaturescanrangefromdiscomfort,ataminimum,toextinction.Long-termchangesintemperaturehavesetentireflorasandfaunasmarchingacrosscontinents,somespeciesthriving,someholdingoninsmallrefuges,andothersbecomingextinct.Areasnowsupportingtemperatespecieswereattimestropicalandatothertimesthefrigidhomesofreindeerandwoollymammoths.

Wedefinedecologyasthestudyoftherelationshipsbetweenorganismsandtheirenvironments.Inchapter4.weexaminetherelationshipbetweenindividualorganismsandtemperature,oneofthemostimportantenvironmentalfactorsinthelivesoforganisms.

CONCEPTS

●Macroclimateinteractswiththelocallandscapetoproducemicroclimates.

●Mostspeciesperformbestinafairly'narrowrangeof

temperatures.

●Manyorganismshaveevolvedwaystocompensatefor

variationsinenvironmentaltemperaturebyregulating

bodytemperature.

●Manyorganismssurviveextremetemperaturesby

enteringarestingstage.

CASEHISTORIES:

microclimates

Macroclimateinteractswiththelocallandscapetoproducemicroclimates.

    Whatdowemeanbymacroclimateandmicroclimate?

Microclimateiswhatweatherstationsreportandwhatwerepresentedwithclimatediagramsinchapter2.Microclimateisclimaticvariationonascaleofafewkilometers,meters,orevencentimeters,usuallymeasuredovershortperiodsoftime,Youacknowledgemicroclimatewhenyouchoosetostandintheshadeonasummer'sdayorinthesunonawinter'sday.Macroclimateandmicroclimateareusuallysubstantiallydifferent.Becausemanyorganismsliveouttheirlivesinverysmallareasduringperiodsoftimerangingfromdaystoafewmonths,macroclimatemaybelessimportantthanmicroclimate.Microclimateisinfluencedbylandscapefeaturessuchasaltitude,aspect,vegetation,coloroftheground,andpresenceofbouldersandburrows.Thephysicalnatureofwaterreducestemperaturevariationinaquaticenvironments.

Altitude

    Aswesawinchapter2（seefig.2.38）,temperaturesaregenerallylowerathighelevations.Theseloweraveragetemperaturesareaconsequenceofseveralfactors.First,becauseatmosphericpressuredecreaseswithelevation,airrisingupthesideofamountainexpands.Theenergyofmotion（kineticenergy）requiredtosustainthegreatermovementofairmoleculesintheexpandingairmassisdrawnfromthesurroundings,whichcoolasaresult.Asecondreasonthattemperaturesaregenerallylowerathigherelevationsisthatthereislessatmospheretotrapandradiateheatbacktotheground.

Aspect

    Topographicfeaturessuchashills,mountains,andvalleyscreatemicroclimatesthatwouldnotoccurinaflatlandscape.Mountainsandhillsidescreatethesemicroclimatesbyshadingpartsoftheland.IntheNorthernHemisphere,theshadedareasareonthenorth-facingsides,ornorthernaspects,ofhills,mountains,andvalleys,whichfaceawayfromtheequator.IntheSouthernHemisphere,thesouthernaspectfacesawayfromtheequator.

Youcanseetheeffectofaspect,inminiature,aroundbuildings.Ifyouwanttowarmyourselfonasunnywinter'sdayintheNorthernHemisphere,yougotothesouthsideofabuilding,toitssouthernaspect,whichfacestheequator.IntheSouthernHemisphere,youwouldgenerallyfindthewarmestspotonthenorthsideofabuilding.Similarly,thenorthernandsouthernaspectsofmountainsandvalleysofferorganismscontrastingmicroclimates.Themicroclimatesofnorth-andsouth-facingaspectsofhillsidesmaysupportverydifferenttypesofvegetation（fig.4.2）.

FIGURE4.2Vegetationonnorth-andsouth-facingslopes.

Vegetation

    Becausetheyalsoshadethelandscape,plantscreatemicroclimates.Forinstance,trees,shrubs,andplantlitter（fallenleaves,twigs,andbranches）produceecologicallyimportantmicroclimatesindeserts.Thedesertlandscape,whichoftenconsistsofamosaicofvegetationandbareground,isalsoapatchworkofsharplycontrastingthermalenvironments.SuchapatchworkisapparentnearKemmerer,Wyoming,acolddesertmuchliketheGobiinMongolia（seefig.2.19）.LiketheGobi,Kemmerercanbebitterlycoldinwinterandblisteringinsummer.Onesummer'sdayRobertParmenterandhiscolleagues（1989）measuredthetemperaturesinvariouspartsoftheKemmererlandscape.Parmenterfoundthatwhilethetemperatureonbaresoilsoaredto48℃,afewmetersawayinplantlitterunderatallshrubthetemperaturewasamoderate21℃（fig.4.3）.Meanwhile,temperaturesunderlowshrubswithlessleafareawereabitwarmerbutstillnotashotassoilintheopen.Asmallorganisminthislandscapecouldchoosemicroclimatesdifferingintemperatureby27℃.

FIGURE4.3Desertshrubsandmicroclimate（datafromParmenter,Parameter,andCheney1989）.

ColoroftheGround

    Anotherfactorthatcansignificantlyaffecttemperaturesisthecoloroftheground.Thisstatementmaysoundabitoddifyouarefromamoistclimate,eithertemperateortropical,wherevegetationusuallycoverstheground.But,aswehavejustseen,muchofthearidorsemiaridlandscapeisbareground,whichcanvarywidelyincolor.Colorshavebeenusedtonamedesertsaroundtheworld,suchasthecentralAsiandesertscalledKaraKum,whichmeansblacksandinTurkish.andKyzylKum,orredsand,andWhiteSands,NewMexico（fig.4.4）.

FIGURE4.4Whiteandblacksands.

Baregroundisthedominantenvironmentofferedbybeaches.NeilHadleyandhiscolleagues（1992）studiedthebeachesofNewZealand,whichrangeincolorfromwhitetoblackandofferawiderangeofmicroclimatestobeachorganisms.Thesebeachesheatupunderthesummersun,butblackbeachesheatupfasterandtohighertemperatures.Theblackbeachesheatupmorebecausetheyabsorbmorevisiblelightthandothewhitebeaches（fig.4.5）.Whenairtemperaturesatbothbeacheshoveredaround30℃,Hadleyandhiscolleaguesfoundthatthetemperatureofthesandonthewhitebeachaveragedaround45℃.Incontrast,theymeasuredsandtemperaturesontheblackbeachashighas65℃.Thoughthesewhiteandblackbeachesareexposedtonearlyidenticalmacroclimates,theyhaveradicallydifferentmicroclimates.

FIGURE4.5Colorofthegroundandtemperature（datafromHadley,Savill.andSchultz1992）.

PresenceofBouldersandBurrows

    Manychildrensoondiscoverthattheundersidesofstonesharborahostoforganismsseldomseenintheopen.Thisispartlybecausethestonescreatedistinctivemicroclimates.E.B.Edney'sstudies（1953）oftheseashoreisopodLigiaoceanicadocumentedtheeffectofstonesonmicroclimate.Edneyfoundthatoverthespaceofafewcentimeters,Ligiacouldchooseairtemperaturesrangingfrom20℃intheopento30℃intheairspacesunderstones,whichheatedtobetween34°and38℃.Thissmall-scalevariationintemperatureissummarizedinfigure4.6.

FIGURE4.6Microclimatesunderstones（datafromEdney1953）.

Animalburrowsalsohavetheirownmicroclimates,inwhichtemperaturesareusuallymoremoderatethanatthesoilsurface.Forexample,whiledailytemperaturesunderashrubintheChihuahuanDesertrangedfrom17.5°to32℃,temperaturesinanearbymammalburrowrangedfrom26~to28℃.Thisburrowwascoolerthanthesurfaceduringthedayandwarmeratnight.Whatdothesedatasuggestaboutthemicroclimatesexperiencedbyplantroots,soilbacteria,andburro