Ecological succession,types , mechanism,example

Ecology

1. VRINDA VINOD
I MSC BOTANY
SN COLLEGE KOLLAM
ECOLOGICAL SUCCESSION

2. Ecological succession
Ecological succession is the orderly appearance and
disappearance of communities or ecosystems in an area in
regular succession,untilan equilibrium state is attained or
a stable final community is established.
It is the sequential replacement of communities and it
culminates in a stable climax with high biomass,complex
species interaction and maximum energy flow .
It is natural ecological as well as evolutionary process by
which an area gets successively colonized by different
communities,untila stable and complex final community
is established

4. Types of Successional communities
Pioneercommunities: it is the first community that develops over a bare
area.Ithas a very little diversity and takes long time to convert the bare area
suitable for the second or seral communities.
Seralor transitionalcommunities: These are communities that develop on an
area during biotic succession between pioneer and climax communities.
Climaxcommunities:itis a stable self perpetuating biotic community with
more complex food webs.

5. ConceptofClimax
Climax community is the final and the more or less stable
stage of ecological succession.
Climax community is in steady state or dynamic equilibrium
because it’s net annual organic production,energylevel and
density of population are almost kept constant.
Two kind of climaxes
Climaticclimax; equilibrium with general climate.
It is not perfectly stabilized for an indefinitely long period.
EdaphicClimax: Equilibrium with soil conditions.

6. Mechanism of ecological succession
Mechanism of ecological succession involves a
continuous, sequential and unidirectional change in
the species composition of a natural community.
It is completed in three broad phases by the operation
of eight major mechanisms.
The three phases are ;-
 1.Initiationphase
 2.Continuationphase
 3.Terminationphase

7. The major mechanisms responsible for ecological
succession include;-
1.NUDATION
2.INVASION
3.ECESIS
4.AGGREGATION
 5.COMPETITION
 6. COACTION
 7.REACTION
8.STABILISATION/ MATURATION

9. Types of Ecological succession
1.Primary & Secondary succession (Based on
starting)
2.Autogenic and Allogenic succesion (Based on
Cause)
3.Autotrophic and heterotrophic Succession
(Based on community)
4.Hydrosere and Xerosere( Based on substratum)

10. PRIMARY SUCCESSION
. Starts from an area where there was no previous
living matter.
. Example –succession on bare rock, newly dug out
pond etc
. First community establishing the new area-
pioneer community (lichen, phytoplankton)
. Relatively slow and long term process
. Seral stages of primary succesion are called
primary seres/priseres.

11. SECONDARY SUCCESSION
. Starts from a previously built-up substratum(already
existing living matter)
. Sudden changes causes the disappearance of the existing
community.
Example –fire, snowfall, biotic interventions
. Thus the area leaving very few organisms and plenty of
organic matter.
. Relatively short tern process and faster than primary
succesion because nutrients are already available and
environmental conditions are more favourable.
The seral stages of secondary succession are called
secondary seres or sub-seres.
Example –succession on fire destroyed grasslands, cleared
forests etc.

12. Based on Cause :
Autogenic / Biotic succession
 It is self driven and it involves the interaction
btw organisms and their environment.
Allogenic succesion
Replacement of existing community by external
conditions and not by the existing organisms.
This is common in polluted ponds, areas of
massive soil erosion etc.

13. Based on Community :
Autotrophic succession
Mainly green plants are the dominant species.
Heterotrophic succession
Detritivorous heterotrophs are the dominant
species (eg:Bacteria, fungi, animals)

14. Based on medium and substratum

Hydrarch succession(Hydrosere)
. Ecological succession in stagnant fresh water bodies,
such as pools, ponds, lakes, marshes, swamps etc.
Starts with the colonisation of the water body by
phytoplanktons which form the pioneer community. From
this stage onwards, succsssion proceeds to climax stage,
represented by large trees or forest.
Different stages of hydrosere are:-
Phytoplankton stageRooted submerged stageRooted
floating stageReed-swamp stagesedge-meadow
stagewoodland stageforest stage.

16. XEROSERE (xerarch succession)
Ecological succession in xeric (dry habitats)such as bare
rocks, wind –blown sand, rocky slopes, etc where there
is an extreme scarcity of water is termed as xerarch
succession.
It is of two kinds.
A)lithosere : succession on bare rocks
b)psammosere : succession in sandy deserts.

18. Mesosere: succession in moderately moist land regions.
Halosere : succession in saline water or saline soil.
Oxylosere: succession in acidic water or soil.