Community Dynamics & ecological succession in biological world pdf

This presentation offers a bird's eye view about community dynamics in general and ecological succession in particular with special reference to Climax vegetation.

1. Dynamics: Succession –Processes, Types; Climax
concepts
By
N. Sannigrahi, Associate Professor
Department of Botany
Nistarini College, Purulia (W.B) India

2. COMMUNITY DYNAMICS
Theword,Dynamics’alwaysstatesthecontinuouschange
fromonestatetoanother.Communitydynamicsistheprocess
andchangeofdevelopmentincommunitiesofallliving
organisms-includingplants,microorganismsandthedifferent
kindsofanimalsoflargeorsmallone.Itisalsocalled
biologicalsuccession.Italsodefinedasthechangesin
communitystructureandcompositionovertimeinducedbythe
environmentalfactors.Communitywithstablestructureissaid
tobeequilibrium.Aftersufferingfromthedisturbances,itmay
ormaynotbringbacktheequilibriumstate.Asthesuccession
levelofcommunity,somespecieswillbegintofindthat
conditionslesssuitableforreproduction.Duetodegreeof
unsuitableconditions,thepopulationdeclinesinnumberand
eventhespeciesmaysufferfromextinction

3. FEATURES
1.Modelsofcommunitydynamicsallowsspeciestodifferin
theirbasicecologyandresponsestoenvironmentalfluctuations
anditmayinvestigatetheextenttowhichthespeciesina
communitydifferconsistentlyinabundancebecauseoftheir
ecologyandexploreshowenvironmentalstochasticity
descriptionofsomethingthathasarandominfluenceupon
communitycompositioninspaceandtime.2.Theruleof
succession-Thereisafundamentalruleofsuccessionthat
drivesallthinkinganddecisionmakingwhendealingwiththe
naturalenvironment;
‘Aspecieswillmoveintoanenvironmentwhentheconditions
aresuitableforitsestablishment,andwillmoveoutofthat
environmentwhentheconditionsbecomeunsuitableforits
reproduction’.
3.Successionandstability-Inalowsuccessionstability,there
arefewspeciespresent.Itisusualfortheirpopulationsto
fluctuatewidelyandoftenrapidly.Theseareusuallyvery
unstable.

4. FEATURES
Ontheotherhand,inhighsuccessionallycommunity,many
specieswithlimitednumbersmayleadtoaverystable
populationsduetotheirgoodrelationshipswiththeother.
Biologicalsuccessionislikeacoiledspring;whencompressed,
successionisretardedbutwhenthecompressiveforceis
released,springrapidlymoveupwards.
Theextentofsuccession-Theultimateorclimaxlevelof
vegetativesuccessioninanyenvironmentisgovernedbyboth
rainfallandlocation’spositiononthebrittlenessscalebutin
antlocationunderappropriatemanagement,morespeciescan
beinducedtoestablish.Insuchcondition,resttendsto
decreasesuccession,leadingtoecologicalstability.Onthe
otherhand,restappliedinthenon-brittleenvironmentleadto
increaseecologicalcomplexity.

5. SUCCESSION
Communityneverstable,butdynamic,changingmoreorless
regularlyovertimeandspace.Environmentisalwayskepton
changingoveraperiodoftimeduetovariousclimaticand
physiographicfactorsandtheactivitiesofthespeciesaround
thecommunitiesthemselves.Theprocesscontinuesand
successivecommunitiesdevelopononeafteranother
communityatthesameplaceuntiltheterminalcommunity
becomesmoreorlessstableforaperiodoftime.The
occurrenceofrelativelydefinitesequenceofcommunitiesover
aperiodoftimeinthesameareaisknownasecological
succession.Differentecologistshaveinterpretedsuccessionin
differenttime.Clements(1916)definedsuccessionas‘the
naturalprocessbywhichthesamelocalitybecomes
successivelycolonizedbydifferentgroupsofcommunitiesof
plants’.

6. SUCCESSION
Odum(1971)preferredtocallthisorderlyprocessas
ecosystemdevelopmentanddefinedinhisownwordsas
successionbasedonthefollowingthreeparameters:
1.Itisanorderlyprocessofcommunitydevelopmentthat
involveschangesinspeciesstructureandcommunityprocess
withtime,itisreasonablydirectionalandtherefore,
predictable.
2.Itresultsfrommodificationofthephysicalenvironmentby
thecommunity,thatis,successioniscommunitycontrolled
eventhoughthephysicalenvironmentdeterminesthepattern,
therateofchange,andoftensetslimitsastohowfar
developmentcango.
3.Itculminatesinastabilizedecosysteminwhichmaximum
biomassandsymbioticfunctionbetweenorganismsare
maintainedperunitof‘availableenergyflow’.

7. CAUSES OF SUCCESSION
Successionismoreproperlyaseriesofcomplexprocessesthat
maybecausedbythefollowing:
1.InitialorInitiatingcauses:Theclimaticfactorssuchas
erosionanddeposits,wind,fire,lightning,volcanicactivities
andvariousbioticinteractionsmayinitiatetheprocessinbare
areasreplacingtheoldone.
2.Ecesisorcontinuingcauses-Thesearetheprocessof
migration,ecesis,aggregation,competition,reactionetcwhich
causessuccessivewavesofpopulationsasaresultofchanges
intheedaphicfeatures.
3.Stabilizingcauses-Thesecausethestabilizationofthe
community.Climateisthemostprofoundcausesof
stabilizationalongwithothersecondaryfactors.

8. FACTORS
Thedifferentfactorslikesiteconditions,charactersofevent
initiatingsuccession(Perturbations),interactionsofthespecies
presentandstochasticfactorssuchasavailabilityofcoloniesor
seedsorweatherconditionsplayaveryimportantroleinthe
succession.Inadditiontothese,humanactionsandclimate
changealongwithgeologyandhistoryofanarea,soiltypealso
playaveryimportantroleinthisregard.Thefactorsofthe
successionarestatedbelow.
1.Theclimaticfactors-Atmospherictemperature,moisture,
humidity,precipitation,sunlightandtheclimaticconditionsof
theneighborhoodregionalsoaffecttheseasonaldevelopment
ofvegetationofanyparticulargeographicalarea.
2.Thebioticfactors-Activitiesoflivingorganismsofplants,
animalsandhumanbeingsplayaveryimportantrole.

9. FACTORS
TheCompetitionsamongplantsforspace,sunlight,wateror
energyalsoplayanimportantroleinthisregard.
3.Thephysiographicfactors-Natureofground.Reliefs(
Mountains,plateaus,plains,faultsetc),altitude,depth,slope
angleetcplayaveryimportantroleinthecauseand
consequencesofsuccession.
4.successionisalsoinfluencedbyfirefactorswhichinclude
bothnaturalforestfiresandman-madeforestfires.The
vegetationcommunityofalargeareacanbehighlyaffectedby
thiskindofconsequencesandthatmayhavedetrimentalaffect
uponthesuccession.
5.theedaphicfactorslikesoilstructureandtemperaturealong
withsoilnutrientsplayanimportantroleinthisregard.

10. TYPES OF SUCCESSION
Thevarioustypeofsuccessionsareasfollows:
1.Primarysuccession-Thesuccessionwhichstartsfromthe
primitivesubstratum,wherethereisnopreviouslyanysortof
livingmatter.Thefirstgroupoforganismsarecalledpioneers,
primarycolonizers.Pioneersarelichen,mossesetc.primary
colonizers.
2.Secondary-Itstartsfrompreviouslybuiltsubstratumwith
alreadyexistinglivingmatter.Theactionofexternalforcelike
suddenchangeinclimaticfactors,bioticintervention,fireetc
causestheexistingcommunitytodisappear.Theareabecomes
devoidoflivingmatterbutthesubstratumbuilduptheareafor
anothersuccessioncalledsecondarysuccession.
3.Autogenic-Aftertheonsetofsuccession,thecommunity
itselfmodifiesitsenvironmentandthuscausingthe
replacementofbynewcommunities.

11. TYPES OF SUCCESSION
4.Allogenic-Replacementoftheexistingcommunityis
causedlargelybyanotherexternalconditionandnotbythe
existingorganisms.Suchcourseisreferredasallogenic
succession.
Onthebasisofsuccessivechangesinnutritionalandenergy
contents,successioncanbethefollowingtypes.
5.Autotrophicsuccession-Itischaracterizedbyearlyand
continueddominanceofautotrophicorganismslikegreen
plants.Fromtheinorganicenvironmenttoorganic
environment,theautotrophicsuccessionscontinuesitsjourney.
6.Heterotrophicsuccession-Characterizedbyearlydominance
ofheterotrophssuchasbacteria,actinomycetes,fungi,animals
etc.Itstartsinapredominantlyorganicenvironmentand
progressivedeclineofenergycontent.

12. PROCESS OF SUCCESSION
Successionisaslowbutsteadyprocessincourseofthe
developmentofcommunitiesfrombarrenlandtilltheclimax
stageisachieved.Theentireprocesscanbedividedunder
differentstagesasfollows:1.Nudation-thisisthe
developmentofbareornudeareacallednudation.Thecauseof
thenudationmaybetopographicsoilerosion,landslide,
volcanicactivity)climaticandbiotic.
2.Invasion–Thisisthesuccessfulestablishmentofaspecies
inabareareaandthespeciesmayderivefromtheotherarea.
Thewholeprocesscomprisesofthethreesub-stages-
A.Migration-Seeds,sporesetcdisseminatedbyair,wateretc
reachtothebarearea.
B.Ecesis-Itistheprocessofestablishmentalongwiththeir
urgetoestablish.
C.Aggregation-Increaseinnumberoftheindividualspecies
andcomeclosetoeachother.

13. PROCESS OF SUCCESSION
3.CompetitionandCoactions-Asaggregationenablesto
multiplythenumber,thereisamasscompetitionsbothintraas
wellasinter-specificoccursforspaceandnutrition.Thisis
calledcompetition.Butindividualsofaspeciesaffecteach
other’slifeinvariouswaysandthisiscalledco-action.Towith
standcompetition,reproductivecapacityandecological
amplitudearethemistdeterminingfactorsinthisregard.
4.Reaction-Themechanismofthemodificationofthe
environmentthroughtheinfluenceoflivingorganisminit
calledreaction.Duetoreactions,changesinsoil,water,
temperaturearenoticed.Duetomodificationofthe
environment,theexistingcommunitybecomesunsuitableand
laterreplacedbyanother-seralcommunity.Thewhole
sequenceofthecommunitieschangesarecalleddevelopmental
stagesorSere.Thepioneersarelikelytohavelownutrients,
moredynamicandtakemineralsinmorecomplexforms.

14. PROCESS OF SUCCESSION
5.Stabilization(climax)–Itisthefinalstageofsuccession.
Climaxcommunityisnearlystableandwillnotchangeuntil
theclimaticandphysiographicconditionschanges.Whenthe
finalterminalcommunitybecomesmoreorlessstabilizedfora
longerperiodoftimeanditcanmaintainitselfinequilibrium
withtheclimateofthearea.
Veryoften,retrogressivesuccessionisalsocoinedinwhich
continuousbioticinfluenceshavesomedegeneratinginfluence
ontheprocess.Duetodestructiveeffectoftheorganisms,
sometimesthedevelopmentofthedisturbedcommunitiesdoes
notoccurandtheprocessofsuccessionbecomeretrogressive
insteadofprogressive.Veryoften,forestmaychangesinto
grasslandandthisisanexampleofretrogressivesuccession.
Sometimesduetochangeoflocalconditionslikemicroclimate,
theclimaxcommunityarelikelytobedifferent

15. PROCESS OF SUCCESSION
Fromthepresumedclimaticclimaxcommunity.Thistypeof
successioniscalleddeflectedsuccession.Veryoften,monsoon
feedareaslikeIndia,differentkindsofcommunitiesare
observedindifferentseasonsofthetear.Itiscalledseasonal
succession(Dudgeon,1921).Thegradualchangesof
successionischaracterizedbythepresenceofdifferent
communitiesasknownas‘Seres’.A‘Presere’isacollectionof
seriesmakingupthedevelopmentofanareafromnon-
vegetatedsurfacestoaclimaxcommunity.Veryoften,
successionofmicro-organismsincludingfungi,bacteria
occurringwithinmicrohabitatisknownasmicro-succession.

16. CLIMAX CONCEPT
Thefinalorstablecommunityinasereistheclimaxcommunityor
climaxvegetation.Itisselfperpetuatingandinequilibriumwiththe
physicalhabitat.Thereisnonetaccumulationoforganicmatterina
climaxcommunity.AccordingtoClassicalecologicaltheoryofF.E.
Clements(1916),successionstepswhentheserehasarrivedatan
equilibriumorsteadystatewiththephysicalandbioticenvironment.
Barringmajordisturbances,itwillpersistindefinitely.Theendpoint
ofthesuccessioniscalledclimax.
CHARACTISTICS
1.Itisthevegetationofthetolerantofenvironmentalconditions,
2.Ithasawidediversityofspecies,agoodspatialstructureand
complexfoodchain,
3.Itistheindexoftheclimateofthearea.Thegrowthforms
indicatetheclimatictype.

17. CLIMAX CONCEPT
4.Individualsintheclimaxstagearereplacedbyothersofthe
samekind.Thusthespeciescompositionmaintainan
equilibrium.
5.Theclimaxecosystemisbalanced.Thereisanequilibrium
betweengrossprimaryproductionandtotalrespiration,
betweenenergyusedfromsunlightandenergyreleasedby
decomposition,betweenuptakeofnutrientsfromthesoiland
thereturnofnutrientbylitterfalltothesoil.
TYPESOFCLIMAX
Differenttypesofclimaxareobservedasfollows:
1.Climaticclimax-Ifthereisasingleclimaxandthe
developmentofclimaxcommunityiscontrolledbytheclimate
oftheregion,itistermedasclimaticcomplex.Maple-beech
communityovermoistsoilisangoodexample.

18. CLIMAX CONCEPT
2.Edaphicclimax-Whentherearemorethanoneclimax
communitiesintheregion.Modifiedbythelocalconditionsof
thesubstrateassoilmoisture,soilnutrients,topography,slope
exposure,fire,animalactivity,itiscallededaphiccomplex.
Successionendswiththeterminationoftheaforesaidfactors.
3.Catastrophicclimax-Climaxcommunitymaybevulnerable
toacatastrophiceventsuchasawildfire.Thechaparral
vegetationwasremovedbythewildfire.Arapiddevelopment
ofherbaceousvegetationfollowsuntiltheshrubdominanceid
re-established.Itiscalledcatastrophicclimax.
4.Disclimax-whenastablecommunityismaintainedbyman
oranydomesticanimals,itisdesignatedasdisclimaxor
disturbanceclimaxoranthropogenicsub-climax.Overgrazing
bystockmayproducedesertcommunityofbushesandcacti
whereasthelocalclimatewouldallowgrasslandfordynamism.

19. CLIMAX CONCEPT
5.Subclimax-Theprolongedstageinsuccessionjust
precedingtheclimaticclimaxiscalledsubclimax.
6.Preclmax&postclimax-Ifthecommunityhaslifeforms
lowerthanthoseintheexpectedclimaticcomplex,itiscalled
preclimax.Butthecommunitythathaslifeformshigherthan
thoseintheexpectedclimaticclimaxispostclimax.Preclimax
stripsaredevelopedinlessmoistandhotterareas,whereas
postclimaxstrandsaredevelopedinmoremoistandcooler
areasthanthatofthesurroundingclimate.
Thus,weseethatthedifferenttypesofclimaxmaydevelopin
thecontextofthedifferentregulatingfactorspresentinthe
community-eithertheedaphicfactorsoftheanthropogenic
factors.

20. THEORIES OF CLIMAX
Anumberoftheorieshavebeenadvocatedinordertoexplain
thecauseandconsequencesoftheclimaxdevelopmentina
particularcommunity.Here,mainlyfourtheorieshavebeen
putforwardtoexplainit.
1.Mono-climaxorClimaticclimaxtheory:Itwasproposedby
Clements(1916).Itmainlyrecognizesonlyoneclimaxandits
characteristicsaredeterminedbysolelyclimate.Theprocessof
successionandthemodificationofenvironmentisovercome
theeffectsofdifferencesintopography,parentmaterialofsoil
andotherhiddenfactors.Thewholeareanowbecomes
enrichedwithuniformplantcommunitySavannahs,Prairies
withgrasslandclimaxinCanada,USAaresomeofthe
examplesinthisregard.

21. THEORIES OF CLIMAX
2.Polyclimaxtheory:AdvancedbyBraun-Blanguet(1932)
andTansley(1935),thistheoryadvocatesthattheclimax
vegetationofaregionconsistsofmorethanonevegetation
climaxesarecontrolledbysoilmoisture,soilnutrients,
topography,slope,exposure,fireandanimalactivity.Thus,
therearedifferenttypes-climaticcomplex,edaphiccomplex
andbioticclimaxdependinguponthesituationtheclimax
vegetationhasdeveloped.
3.Climaxpatterntheory:ItwasproposedbyWhittaker(1953).
Itrecognizesavarietyofclimaxgovernedbyresponsesof
speciespopulationstobioticandabioticconditions.Thetotal
environmentoftheecosystemdeterminesthecomposition,
speciesstructureandbalanceoftheclimaxcommunity.The
environmentincludesthespeciesresponsetomoisture,
temperatureandnutrients,theirbiotic

22. THEORIES OF CLIMAX
relationships,availabilitytofloraandfaunatocolonizethe
area,thechanceofdispersalofseeds,soil,climateand
disturbancesuchasfireandwind.Theclimaxcommunity
representsapatternofpopulationsthatcorrespondstoand
changeswiththepatternofenvironment.
4.Informationtheory:Accordingtothismodel,thecommunity
isconsideredasthermodynamicunit.Intheseralstage,the
dissipationenergylessthantheinputenergy.Thereismorenet
productionandasthetimetravels,communitygrows.
Although,attheinitialstage,diversityislowbutwiththe
passageoftime,totalinformationinthecommunityincreases.
Intheclimaxcommunity,theinputenergymoreorlessequal
toorslightlyhigherthanoutputenergy.

23. TIME FACTORS FOR SUCCESSION
Primarysuccessiononsanddunes-----1000years
Secondarysuccessiononabandonedagriculturalland-100
yearsintropicalclimateand200yearsintemperateclimate,
Secondarysuccessioningrasslands-50-60yearsunderthe
followingsub-stages:
Annualweedstage:2-5years
Shortlivedgrass:3-10years
Perennialgrassstage:10-20years.
Theclimaxgrasslandstage:20-40years.
Successionbeginsinwateryhabitatlikeponds,marshesand
otherstandingwaterisknownashydrachandthedifferent
stagesofsuccessioncalledhydrosereandinsandlikedesert
areascalledxerosere.

24. IMPORTANCE OF SUCCESSION
1.Theecologicalsuccessionconveystheimportanceofseral
stagesproductivityalthoughcomparativelylessstable.The
climaxcommunityismatureandstablewithgreaterbiological
diversity,largerinnumberandenergyflow.
2.Theclimaxcommunityisveryimportantasfaras
productivityconsideringitasmultipleusesystem.Here,the
P/RratioinsuchcommunityisoneandthereisleastforNPP
harvesting.
Theearlysuccssionalstagesactassourceoffoodfor
heterotrophy.
Thesecondarysuccessioncanmaletheroadforrenovationof
devastatedareatobeaclimaxone.
Theconversionofspoiltosoilenhancedbythejourneyof
succession.

25. THANKS FOR Your visit
ACKNOWLEDGEMENT
1.Google for images
2.Different WebPages for content
3.Ecology & environment-P.D.Sharma
4.Ecology & Environmental Biology-T.K.saha
5. A text book of Ecology-S. Chand& Company.
6. Plant Ecology & Phytogeography-ArunChandra Sahu
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