2. Succession
The term ecological succession was first given by Hult
(1885). Community are never stable but keep on
changing. This relatively definite sequence of
communities over a period of time in the same area is
called ecological succession.
Communities are never found permanently in
complete balance with their component species or
with the physical environment.
Succession is a universal process of directional change
in community composition, on an ecological time
scale.
3. Eventually succession slows as the community
reaches a steady equilibrium with the environment .
Successional changes include structural and
functional changes.
Causes of succession
Generally there are three main causes of succession
1. Initial or initiating causes- Biotic and climatic are
the initials of succession. Factors such as erosion,
deposits, wind and fire etc., caused by lighting and
volcanic activity, and latter various activities of
organisms.
These causes produces bare areas or destroy the
existing population in an area.
4. 2. Ecesis or Continuing causes- These are the process
as migration, ecesis, aggregation, competition
reaction etc., which causes successive waves of
populations as a result of changes, chiefly in the
edaphic features of the area.
3. Stabilising causes- These causes the stabilisation of
the community. According to Clements, climate of
the area is the chief causes of stabilisation, other
factors of area have secondary value.
5. Basic type of succession
Primary Succession - succession occurring in bare
areas such as on a new volcanic island, where no
community existed before is called primary
succession.
The first group of plant or organism establishing
there are known as the pioneers, primary community
or primary colonisers.
Pioneers are able to develop on nutrient poor and
that often have unfavourable moisture condition.
Pioneers are cyanobacteria, lichens and bryophytes.
6. SecondarySuccession- The secondary succession
starts on a well developed soil already formed at the
site. Secondary succession are comparatively more
rapid.
It occurs at a site from where an already developed
community has been destroyed by natural
disturbance such as fire or flooding. It is more
common type of succession.
Autogenic Succession- When the succession has
began the vegetation itself is responsible for replacing
itself by changing existing environmental conditions.
Autogenic succession is self-driven, resulting from the
intration b/w the organism and their environment.
7. Allogenic Succession- Allogenic succession occurs as a
result of the changes brought about in the habitat by
external agencies not by existing community itself.
Autotrophic Succession- The succession where initially
the green plants are much greater in quantity than
the animals, is known as the autotrophic succession.
it begins in a predominantly inorganic environment
and the energy flow is maintained indefinitely. There
is a gradual increase in the organic matter content
supported by energy flow.
8. Hetrotrophic Succession- It is characters iced by early
dominance of heterotrophs such as animals, fungi,
bacteria, actinomycites.
It begins in a predominantly organic environment and
there is a progressive decrease in the energy content.
Progressive Succession- When succession occur in
direction of simple community to complex community
known as progressive succession.
Retrogressive Succession- when succession occur
from complex community to simple community.
9.
10.
11. Depending upon the substratum
1. Hydrosere or Hydrach- Succession beginning in
fresh water. Ex. Ponds, Lakes, Streams etc.
2. Xerosere or Xerarch- Succession beginning in dry
conditions. It is classified into three classes
I. Lithosere- When sucession starts on bare
rocks.
II. Pasmosere- When succession begins on sand.
III. Halosere- When succession starts in saline
conditions
3. Mesarch- when succession begins in mesic
conditions
12. Mechanism of Succession
According to Clements succession is a process
involving several steps---
1) Nudation- Succession begins with the
development of a bare area without any form of
life. The area may develop due to several caueses
such as landslide, erosion, deposition or other
catastrophic agency. The causes of nudation may
be----
• Topographic- Due to soil erosion by gravity, water
or wind the existing vegetation may disappear.
• Climatic- Glaciers, dry period, hails, and stones,
forest may also destroyed the vegetation.
13. • Biotic-Man is most important factor which is
responsible for destruction of forest, grassland for
industry etc.
2. Invasion- This is a successful establishment of a
species in a bare area. The species actually reaches
this new site from any other area. This process
complete in three stages-
I. Migration (Dispersal)- The seeds, spores or other
propagates of the species reach the bare area.
This process is known as the migration. Migration
does not change the size of population.
14. I. Ecesis(Establishment)- After reaching the new
area, the process of successful establishment of
the species as a result of adjustment without the
condition prevailing there is known as ecesis.
Ecesis is able to sexually reproduce in that
particular area.
II. Aggregation- Aggregation as a result of
reproduction, the individuals of the species
increase in number, and they come close to each
other.
15. 3). Competition or Coaction- After aggregation of
individuals in an area leads to interspecific and
intraspecific competition for limited place and
nutrition. Individuals of a species affected
each other is life in a various way and this is called
coaction.
4). Reaction- This is a most important stage in
succession . The mechanism of the modification of
the environment through the influence of living
organism on it is known as a reaction. As a result
of the reaction changes take palce in soil, water,
light conditions, temp, and many other factors of
the environment. When the environment get
modified become unstable for existing community,
and is eventually replaced by another community.
16. 5). Stabilization Climax- The whole process of succession
results in stabilization of the
vegetation which is now in complete harmony with the
environment of that place.
The final community become equilibrium with their
environment. This final community
and the stage as climax stage.
Hydrosere
1. Phytoplankton
2. Submerged Stage
3. Floating Stage
4. Reed-Swamp Stage
5. Sedge-Meadow Stage
6. Wooland Stage
7. Climax Stage
