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.Atentativesuggestionbyacarefulworker