What is ecology.docx

What is ecology.docx

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Whatisecology

Introduction

1.1Whatisecology?

Ecologyisthestudyoforganismsinrelationtothesurroundingsinwhichtheylive.Thesesurroundingsarecalledtheenvironmentoftheorganism.Thisenvironmentismadeupofmanydifferentcomponents,includingotherlivingorganismsandtheireffects,andpurelyphysicalfeaturessuchastheclimateandsoiltype.

Ecologists,thosewhostudyecology,arealwaysaimingtounderstandhowanorganismfitsintoitsenvironment.Theenvironmentisofsupremeimportancetoanorganismanditsabilitytoexistintheenvironmentwhereitliveswilldetermineitssuccessorfailureasanindividual.Thismeansthatmuchofthisbookisreallyaboutthestudyofenvironmentsfromthepointofviewofvariousorganisms（butseeChapter9whichdescribesindetailwhatmakesupandaffectsanenvironment）.

Thereareseveraldefinitionsofecology.Many

workershaveproducedtheirowndescriptionofthis

branchofbiology.Thewordecologywasfirstusedby

aGermancalledErnstHaeckelin1869.Itcomes

fromtwoGreekwordsoikosmeaninghomeandlogos

meaningunderstanding.Haeckeldescribedecology

as'thedomesticsideoforganiclife'and'theknow-

ledgeofthesumoftherelationsoforganismstothe

surroundingouterworld,toorganicandinorganic

conditionsofexistence'.This'surroundingouter

world'isanotherwayofsayingtheenvironment.In

1927CharlesEitonwrotethatecologyis'thestudy

ofanimalsandplantsinrelationtotheirhabitsand

habitats'.Todayanecologistwouldprobablysubsti-

tutetheword'organisms'for'animalsandplants'

becausewenowrecogniseothercategoriesoforgan-

isms（fungi,protoctistsandbacteria）whicharenot

intheplantoranimalkingdoms.Manyoftheseare

extremelyimportantinecologyalthoughtheyare

seldomaswellstudiedastheplantsandanimals.

MorerecentlyKrebs（1985）hasdefinedecologyas

'thescientificstudyoftheinteractionsthatdetermine

thedistributionandabundanceoforganisms'.You

maytakeyourpickastowhichdefinitionyouprefer.

Ecologyislikeanenormousjigsawpuzzle.Each

organismhasrequirementsforlifewhichinterlock

withthoseofthemanyotherindividualsinthearea,

Someoftheseindividualsbelongtothesamespecies,

butmostareverydifferentorganismswithvery

differentwaysoflivingorinteracting.Figure1,1isa

diagrammaticrepresentationofthisinterlocking

jigsaw.Itillustratessomeofthewaysinwhichasingle

individualfitsinwithothers.Inthiscaseananimal

isrepresentedwhichcatchesotheranimalsforfood

（itisapredator）andwhichinturnishuntedand

maybekilledbyanotherspeciesofpredator.During

theanimal'slifetimeitneedstofindamateofthe

samespeciestoproduceoffspring.Duringitslifeit

alsocompeteswithotheranimals（competitors）for

foodandwillprobablycatchdiseases.

Theabilityoftheanimaltoavoidthepredator,

catchitsprey,withstanddiseaseandsoonwill

FigureI.IDiagramshowingtheinterlockingnatureof

thefeaturesoftheenvironmentwhichinfluencean

organism.Inthiscasetheorganismisapredator,butto

generalisethediagram,theword'prey'couldbereplaced

by'food',or,foraplant,bylightandnutrients'.For

simplicity,thisfigureistwodimensional,buttheecological

interactionsoforganismsandtheirenvironmentare

reallymulti-dimensional,

dependontherelationshipsithaswiththeorgan-

ismsaroundit.Itslifewillalsobeaffectedbythe

weather,timeofyearandthequalityofnestingor

sleepingsites.Infact,thissimplifiedexampleis

alreadybecomingcomplicatedasmoreandmore

piecesofthepuzzleareadded.Thestudyofthese

ecologicalrelationshipsfromthepointofviewofa

singlespecies,asisillustratedbyFigureI.I,iscalled

autecology（seeChapter3）.Ifallthespeciesliving

togetherarestudiedasacommunity（seeChapter

14）thenthisstudyiscalledsynecology.

1.2Thenatureofecology

Theonlywaytofindouthowanyorganismsurvives,

reproducesandinteractswithotherorganismsisto

studyit.Thismakesecologyapracticalscience.

Therearethreemainapproachestothestudyof

ecology.Thesimplestmethodistoobserveandrecord

theorganisminitsnaturalenvironment.Thisis

sometimesdescribedasobservation'inthefield'or

fieldwork,althoughthetermcanbeconfusingas

'field'suggestsopengrasslandsorthesiteofhuman

cultivation.Asecondtypeofstudyistocarryout

experimentsinthefieldtofindouthowtheorganism

reactstocertainchangesinitssurroundings.Athird

approachinvolvesbringingorganismsintoacon-

trolledenvironmentinalaboratory,cageorgreen-

house.Thismethodisveryusefulasitisofteneasier

torecordinformationundercontrolledconditions.

However,itmustberememberedthattheorganisms

mayreactdifferentlybecausetheyhavebeen

removedfromtheirnaturalhome.

Nosinglestudycanhopetodiscovereverything

thereistoknowabouttherelationshipsbetweenan

organismanditsenvironment.Theserelationships

aresovariedthatdifferentkindsofinvestigationare

neededtostudythem.Oftenbothstudyinthenatural

environmentandexperimentsinthelaboratoryare

requiredtodiscoverevenpartofthepicture.Also,as

theenvironmentchanges,soanorganismmay

responddifferently,withtheresultthatanexperi-

mentunderonesetofconditionsmaywellgivedif-

ferentresultstothesameexperimentcarriedout

underdifferentconditions.

Sowehaveapictureofecologyasasubjectfullof

complexitywhereanorganismhasmanydifferent

responsesandneeds.Theoretically,therefore,thereis

analmostinfiniteamounttobediscoveredabout

theecologyoftheworld.Evenafteracenturyof

ecologicalstudywearejustscratchingthesurfaceof

possibleknowledge.Alargeamounthasbeendiscov-

eredovertheyears,butourknowledgeispatchy;we

knowfarmoreaboutnorthernhemisphere

temperatewoodlandthanweknowabouttropical

rainforest,moreaboutEnglishrockyseashoresthan

theAustralianbarrierreef.

1.3Thestudyofecology

Whatmakesecologyexciting,ratherthanan

endlesslistofthingstobelearnedaboutorganisms,

isthatwearestudyingaliving,workingsystem.

Becausethesystemfitstogethersoneatlyitforms

repeatedpatternswhichcanberecognisedbythe

ecologist.Organismswithsimilarlifestylesoften

respondtotheirenvironmentinsimilarways.For

exampleourpredatorinFigureI.Icanonlycatchits

preyincertainways.Ifitspreybecomesscarceit

maystarve,eatsomethingelseormigratetowhere

foodismoreplentiful.Inotherwordsitonlyhasa

certainnumberofoptionsanditsresponsetocertain

conditionsmaywellbepredictable.Understanding

whyorganismsreacttovariousconditionsinone

wayratherthananothertakesusalongwaytowards

anunderstandingoftheprinciplesofecology.

Theseprinciples,withwhichthisbookiscon-

cerned,areonlybecomingunderstoodbecauseofthe

manystudiesoforganismsbothinthefieldandin

thelaboratory.Throughoutthisbookyouwillfind

examplesofhowparticularorganismsrelatetotheir

environmentgivenasevidencetosupporttheprinci-

plesbeingdescribed.Becausetherelationshipof

organismstotheirenvironmentmaybeverysubtle,

itcanoftenbedifficulttounravelthesituationtodis-

covertheprinciplesinvolved.Yetfindingouthow

organismsinteractandapplyingtheseprinciplescan

beanabsorbingandfascinatingpursuit.

1.3Thestudyofecology

Anecologistcouldstartanystudybyaskingthe

question:

'Whydoesthisorganismliveorgrowhere

andnotthere?

'.Insimplifiedtermsthisistheques-

tionecologicalinvestigationsoftentrytoanswer.Of

courseitisfartoodifficulttoanswerinonegoand

canbesplitupintomanydifferentquestions.The

firstandmostobviousquestionis:

'Wheredoesthe

organismorspeciesIamstudyinglive?

'.Usuallythis

canbeansweredbycarefulobservationinthefield

withthehelpofsomesortofsamplingmethod.Once

weknowthisotherquestionsmaybecomeobvious.

Forexampleanecologistmayask:

Howdoestheorganismobtainitsfood?

Isaparticularnutrientlimitingitsgrowthor

numbers?

Issomethingelselimitingitsgrowthornumbers?

Doesitreproduceinthissiteandifsohow?

Isitabsentfrompartsofthesiteduetosomefactor?

Howandwhendotheyoungdisperse?

Whatcausesthedeathoftheorganisms?

Therearenumerouspossiblequestions,someof

whichmaybeuniquetoaparticularsituation.

Obviously,ifanecologicalinvestigationstartswith

specificquestions,orobjectives,itmakesthetaskof

studyingtheecologyoforganismsmucheasier.

Boxl

Experimentaldesign

Assomuchofourecologicalknowledgecomesfrom

experimentsitisworththinkingabouthowexperimentsare

designed.Theskillandcarewithwhichanexperimentis

plannedandcarriedoutwillaffecttheaccuracyofthe

informationcollectedandthewayinwhichtheresultsare

interpreted.Becriticalwhenreadingotherpeople'sexperi-

mentaltechniquesandtheirinterpretationoftheresults.They

mayhavemademistakes.Eveniftheyhavenot,youwillbe

practisingtheimportantscientificskilloflookingatand

analysinginformationwithanopenmind.Watchoutforpoorly

designedexperiments-thereareseveralabout,eveninthe

literature!

Ifyouwanttousesomefindings,butonlyhavea

reportoftheworkbyathirdparty,trytogetacopyofthe

originalpublication.Atentativesuggestionbyacarefulworke