Chapter 09ECOSYSTEM AND ITS PRODUCTIVITY.docx
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Chapter 09ECOSYSTEM AND ITS PRODUCTIVITY.docx
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Chapter09ECOSYSTEMANDITSPRODUCTIVITY
Chapter09ECOSYSTEMANDITSPRODUCTIVITY
Anecosystemisacommunityoforganisms(bioticcomponent)andthephysicalenvironment(abioticcomponent)interactingasaunit.
∙Thecommunityandthehabitatareintimatelyinteractingbyactionsandreactions:
everythingisconnectedtoeverythingelse.
∙Speciesmayhaveadirectorindirecteffectonotherspecies.
Theecosystemrepresentsabroadervieworhigherleveloforganizationthancommunity.
COMPONENTSOFECOLOGICALSYSTEMS
Allecosystemsarecomposedofabioticandanabioticcomponent.
Thethreebasicstructuralandfunctionalcomponentsconsistofautotrophs,heterotrophsandinorganicanddeadorganicmatter.
1.Autotrophsaretheenergy-capturingbaseofthesystem.
2.Heterotrophsconsistofconsumersanddecomposers.
∙Consumerseatmostlylivingtissue.
∙Decomposersutilizeddeadorganicmatterandconvertedtoinorganicsubstances.
3.Detritusismadeoforganicandinorganicsubstancesinaquaticsystems,andthesoilmatrix.
Inputsinthesystemarebothbioticandabiotic.
∙Abioticinputsareinorganicsubstances(CO2,N,O2,etc.),mineralnutrients,organiccompounds(proteins,carbohydrates,humicacid,etc.),precipitation,andradiantenergy(heatandlight).
∙Bioticinputsincludeorganismsthatmoveintotheecosystemaswellasinfluenceimposedbyotherecosystemsinthelandscape.
Thedrivingforceofthesystemistheenergyofthesun,whichcausesallotherinputstocirculatethroughthesystem.
Consumersregulatethespeedatwhichnutrientsrecyclethroughthesystem.
Mostecosystemsdonothavedistinctboundaries.Boundariesdescribedinmostcasesarearbitrarysubdivisionsofacontinuousgradationofcommunities.
Ecosystemschangewithtime:
organismsliveanddie,immigrateandemigrate,etc.
Ecosystemsaresubjecttodisturbances:
floods,fire,storms,etc.
Ecosystemspossessatrophicstructurethatprovidesthepathwayforthemovementofmaterialsbetweentheabioticandbioticenvironment.
THENATUREOFENERGY
Solarradiationinvolveslightandthermalenergy
Solarenergydrivesthemovementofwaterbetweentheearthandtheatmosphere,andthewaterdistributionintheenvironment.
Lightistheenergysourceofphotosynthesis,affectsthedistributionoforganismsinlandandwater,andtheirdailyactivities.
ENERGYDEFINED
Energyistheabilitytodowork.
Workiswhathappenswhenaforceactsthroughadistance,expressedasforcexdistance.
Kineticenergyistheenergyofmotion.
Potentialenergyisstoredenergy.
Chemicalenergyisthepotentialenergystoredinthebondsofmolecules.Itisparticularlyimportantinlivingsystems.
Chemicalenergycanbetransformedintokineticenergy.
∙Calorieistheamountofheatnecessarytoraise1gram(1ml)ofwater1ºCat15ºC.
∙IntheSI(SystèmeInternationale)theunitusedisthejoule.1joule=4.168cal.
∙ThekilogramcalorieorCalorieisusedforlargequantities:
1Cal=1000cal.
∙ABTUorBritishthermalunitistheamountofheatrequiredtoraise1poundofwater1ºF.
∙1BTUequals252cal.
LAWSOFTHERMODYNAMICS
Thermodynamicsisthestudyofenergyanditstransformations.
∙Systemistheobjectbeingstudiedinthermodynamics.
∙Surroundingistherestoftheuniverseotherthanthesystem.
∙Closedsystemsdonotexchangematterorenergywithitssurroundings.
∙Opensystemsexchangematterand/orenergywiththesurroundings.
1.Firstlawofthermodynamics.
∙Energycanbetransferredandtransformed,butitcannotbecreatedordestroyed.
∙Energyoftheuniverseisconstant.
∙Energy-masscannotbecreatednordestroyed.
∙ThislawisalsoknownasthePrincipleofConservationofEnergy.
2.Secondlawofthermodynamics.
∙Theentropyoftheuniverseisincreasing.
∙Entropyisameasureofthedisorderorrandomnessofasystem.
∙Everyenergytransferortransformationincreasesthedisorderintheuniverse.Itincreasestheentropyoftheuniverse.
∙Whenenergyisconvertedfromoneformtoanother,someoftheusableenergyisconvertedtoheatandisdispersedinthesurroundings.
∙Ateverystepofenergytransformationthereisalossofenergycapabletodowork.
Nooneprocessthatrequiresenergyconversionis100%efficient.Someenergyisalwayslostintheformofheat,therandommotionofmolecules.
Energylostinatransfercannotperformwork.Thisenergyendsupasheatcontributingtothedisorganizationandrandomnessofthemolecules.
Entropyordisorderinaclosedsystemtendstoincreasespontaneouslyovertime.
Heatistheenergyofrandommolecularmotion.Moleculesandatomschangetheirkineticenergybecauseheatflowsinoroutofthem.
∙Theheatcontentofthatsampleofgasisthesumofitsenergies,internalandexternal,exceptnuclearenergy,ofallitsmolecules.
∙Theinternalenergyofamoleculeconsistsofthemotionsofthenucleiandelectronsoftheatomsofthemolecule.Themotionsofthenucleiarenottobeconfusedwithnuclearenergy,whichisinsideanucleus.
Heatenergyislessorganizedandhashighentropy(S).Itistheuncoordinatedmovementofmolecules.
Livingsystemsareorderlyandrequireenergyinordertomaintaintheirorderliness.
Inopensystems,aslongasthereisaconstantinflowofenergyandmattertothesystem,andaconstantoutflowofentropy(heatandwaste),thesystemmaintainsasteadystate.
∙Lifeisanopensystemmaintainedinasteadystate.
Energyflowsintoecosystemsintheformoflightandleavesintheformofheatafteraseriesoftransformationswithintheecosystem.
Organismsincreasetheentropyoftheuniversebyreleasingsmallmoleculesandheatintotheirsurroundings.Thesemoleculesandheatenergycomefromthemoreorganizedmoleculesoffood:
starch,proteins,etc.
CYCLINGOFENERGYINECOSYSTEMS
Visiblelightistheportionoftheelectromagneticspectrumbetween400and740nm.
ThesewavelengthsareknownasthephotosyntheticallyactiveradiationorPAR.
∙Nearinfrared:
740to5000nm.
∙Farinfraredorthermalradiation:
5000to100,000nm.
∙Ultraviolet–A:
315to380nm.
∙Ultraviolet–B:
280to320nm.
PRIMARYPRODUCTION
Energyaccumulateinplantsthroughphotosynthesisiscalledprimaryproduction.
Thisenergyisstoredinchemicalbonds.
Grossprimaryproduction(GPP)istotalenergystoredbyautotrophsinanecosystem.
∙Neworganicmatterisbeingmade.
Thestoredenergyleftafterplantrespirationisthenetprimaryproduction(NPP).
∙NPP(netprimaryproduction)=GPP(grossprimaryproduction)-R(respiration)
Productivityistherateatwhichorganicmatteriscreatedbyphotosynthesis,gdrywt/m2/year.
Productivityisthenameusedforproductionrates.Therateatwhichenergyaccumulatesasbiomass.
∙Productionrates=productionpertimeunit,e.g.kilocaloriespersquaremeterperyear,Kcal/m2/yearorgramsofdryweightpersquaremeterperyear,
gdrywt/m2/year.
∙Kilocalories/squaremeter/yearorgramsofdryweight/squaremeter/year.
Grossprimaryproductivityisthetotalphotosynthesisinatimeperiod.
Secondaryproductionistheenergystoredinconsumers.
∙Itisassimilatedenergy.
∙Noneworganicmatterismade.
∙Itreferstotheenergystoredaftertheconsumer'srespirationhasalreadybeensubtracted.
Theaccumulatedorganicmatterfoundonagivenareaatagiventimeisthestandingcropbiomass.
Biomasscanbedefinedasthemassoforganismsperunitareaandisusuallyexpressedinunitsofenergy(e.g.,joulesm-2)ordryorganicmatter(e.g.,tons/haorgramsdrywieight/m2).
Biomassisamountpresentatanygiventime,gdrywt/m2.
∙Productivityisarate;biomassisnotarate.
Biomassdoesnotincludeanyplanttissueeatenbyherbivoresorlostthroughdeathpriortotheperiodofmeasurement.
ENVIRONMENTALCONTROLSONPRIMARYPRODUCTIVITY
Temperatureandmoisturecontrolprimaryproductivity.
Primaryproductivityisafunctionoftherateofphotosynthesisandthetotalsurfaceareaofleavesthatarephotosynthesizing.
Extremelycoldandhottemperatureslimittherateofphotosynthesis.
Withintherangeoftemperaturesthataretolerated,ratesofphotosynthesisrisewithtemperature.
Mostbiologicalmetabolicactivitytakesplacewithintherange0to50°Celsius.Thereislittleactivityaboveorbelowthisrange.Theoptimaltemperaturesforproductivitycoincidewith15to25°Celsiusoptimalrangeofphotosynthesis.
Thegrowingseasonistheperiodwhentemperaturesaresufficientlywarmtosupportphotosynthesisandnetprimaryproductivity.
Warmertemperaturessupportbothhigherratesofphotosynthesisandalongergrowingseason,resultinginahighernetprimaryproductivity.
Theamountofwateravailabletotheplantwillthereforelimitboththeratesofphotosynthesisandtheamountofleavesthatcanbesupported.
Theinfluenceoftemperatureandwateravailabilityisinterrelated.
Itisthecombinationofwarmtemperaturesandadequatewatersupplytomeetthedemandsoftranspirationthatresultsinthehighestvaluesofprimaryproductivity.
PATTERNSOFPRIMARYPRODUCTIVITYINECOSYSTEMS
Variationamongecosystems
Themostproductiveterrestrialecosystemsaretropicalrainforestswithhighrainfallandwarmtemperatures.Theirproductivityrangesbetween1000and3500g/m2/year.
Temperateforestswithlowertemperaturesandrainfallrangebetween600and2500g/m2/year.
Temperategrasslandproductivityisaround500g/m2/year.
Articandalpinetundrahaveaproductivityof0to200g/m2/year.
Productivityoftheopenseaisgenerallyquitelow.
Productivityintheopenwatersofthecooltemperateoceanstendstobehigherthanthos
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