Ecological
succession
What is ecological succession?
Explain various kinds of succession.
“
Ecological succession may be defined as on orderly and progressive replacement
of one community by another community until reaching stable community occupies
in that area”.
Or
“Successive
replacement of same habitat by different communities over a period of time in
particular area is called ecological succession.”
Ecological
succession is a sequential process of community development which result in
formation of climax community in the environment. The succession gives us an
idea that never stand still everywhere, it is continuous process of changes.
According
to the habitat there are various kinds of succession, which are as follows.
Hydrach:
Succession begins in water habitat like pond, marshes, etc is called
hydrach. Various stages of development
of hydrach constitutes hydrosere.
Xerach: when succession began in dry land
(and deserts, sand dunes, salt deserts, rock deserts etc.) are termed as
xerach. Various stages of development of
xerach are called xerosere.
When
succession started on bare area, is called as lithosere. When succession started from sand is called
psamosere. But when succession began on
the region or inter habitat between water and sand it is termed as
mesorch.
Kinds of succession: Ecological succession may be
•
Primary
succession
•
Secondary
succession
•
Autotrophic
succession
•
Heterotrophic
succession
Primary succession:
When
succession proceeds from bare area i.e. area devoid of organism or an area
which has not been changed by organism, then it is termed as primary
succession.
Secondary succession:
If
succession stared on the area previously
having community and has organically rich soil, then it is termed as secondary
succession.
3. Autotrophic
succession:
it is characterized by early and continuous dominance of autotrophic organisms
like green plants. Autotrophic
succession began in pre-dominantly on inorganic environment. The green plants converting inorganic
components into organic matter in substratum.
4. Heterotrophic succession. It is characterized by an early dominance of
heterotrophic organisms like, bacteria, fungi, protozoan, and animals. Heterotrophic succession begins in predominantly organic environment. The
heterotrophic organisms e.g. bacteria, actinomycetes, fungi, converting
organic components into inorganic matter declining energy.
What is ecological succession?
Explain the requirements of succession?
Or
What is ecological succession?
Explain the process of ecological succession?
“
Ecological succession may be defined as on orderly and progressive replacement
of one community by another community until reaching stable community occupies
in that area”.
Or
“Successive
replacement of same habitat by different communities over a period of time in
particular area is called ecological succession.”
Ecological
succession is a sequential process of community development which result in
formation of climax community in the environment. The succession gives us an
idea that never stand still everywhere, it is continuous process of changes.
General process of ecological
succession.
Complete
process of primary autotrophic ecological succession involves following steps
which are followed one another.
•
Nudation
•
Invasion
•
Ecesis
•
Aggregation
•
Reaction
•
Stabilization
Requirements of succession
Succession involves following
phases:-
Nudation: Succession begins with the
development of a bare area, called Nudation (disturbance). Nudation may be
caused due to several reasons such as
volcanic eruption, flood, erosion (physiographic, climatic and biotic agents).
Invasion: (Entry or arrival) invasion is
arrival or entry of reproductive bodies of various organisms from some other
area is called invasion. It refers to arrival or migration of propagules. Thus
entry of organism is called as invasion.
Ecesis: if conditions are favorable some of
the migrant get germinate in new area and starts to reproduce. Thus, it involves establishment and initial
growth of migrant is called ecesis.
Generally plant community are the pioneer.
Aggregation: increase in number of individuals
of invaded species. As vegetation became
well established, grew, and spread, various species began to compete. Increased
population leads to competition for space, light, water, soil etc. competition results in decrease in
number. The competition between members
of same community or same species is called intra-specific competition. If
competition between individuals of different species is called inter-specific
competition.
Reaction: The competing organism modifies the
environmental factors such as, soil, moisture, temperature, gases, etc. the
changed conditions become unfavorable for the pioneer, but better suited for
new comer (Invader). During this phase
autogenic changes affect the habitat resulting in replacement of one community
by another. Thus, the pioneer community
are replace by another community through sequence of new invasions.
Stabilization: Sequential replacement results at
last in stabilization of community, called climax community. Which, is the
final stage of ecological succession. It
is not affected by environmental changes.
Hence, it remain stable for long period.
On the margin of climax community
another stable communities are develops called as Pro-climax community. Some time strip of community of higher life
form within the climax community are develops called as post climax
community.
Write short Note?
Concept of climax community. Or
Theory of climax community.
“
Ecological succession may be defined as on orderly and progressive replacement
of one community by another community until reaching stable community or climax
community occupies in that area”.
On
the margin of climax community another stable communities are develops called
as Pro-climax community. Some time strip
of community of higher life form within the climax community are develops
called as post climax community.
There are two prominent theories
have been concerned with climax community are as follows.
•
Mono-climax
•
Poly-climax
•
Mono-climax: this theory was advance by Patrick
Clement. According to this theory there
is only one climax community in an climatic area. The another communities which are present in addition to climatic community are regarded as
sub-ordinate communities. The term
pro-climax and post-climax are used to define sub-ordinate community.
•
Poly-climax: This theory was advanced by
Whitaker. According to this theory,
numbers of climax community are present in an climatic area. The pro-climax and post-climax communities are
nothing but the different climax
communities
Ex. 1. Hydrach 2. Xerach.
Hydrach
“
Ecological succession may be defined as on orderly and progressive replacement
of one community by another community until reaching stable community or climax
community occupies in that area”.
Hydrach:
Succession begins in water habitat like pond, marshes, etc is called
hydrach. Various stages of development
of hydrach constitutes hydrosere.
Following are the various stages of
development of hydrach (Hydroseres)
•
Phytoplankton stage:
•
Submerged stage
•
Floating stage
•
Reed swamp stage
•
Sedge-meadow stage Or Marginal stage
•
Woodland stage
•
Climax stage
Phytoplankton stage:
Unicellular
floating algal plants such as diatoms are pioneer species of a bare water body,
such as a pond. Their spores are carried by air to the pond.
The
phytoplankton are followed by zooplankton.They settle down to the bottom of the
pond after death, and decay into humus that mixes with silt and clay particles
brought into the basin by runoff water and wave action and form soil. As soil
build up, the pond becomes shallower and further environmental changes.
Submerged stage
As
the water body becomes shallower, more submerged rooted species are able to
become established due to increasing light penetration in the shallower water.
This is suitable for growth of rooted submerged species such as Myriophyllum, Vallisneria, Elodea, Hydrilla, and Ceratophyllum. These plants root themselves in mud. Once submerged
species colonize the successional changes are more rapid and are mainly
autogenic as organic matter accumulates. Inorganic sediment is still entering
the pond or lake and is trapped more quickly by the net of plant roots and
rhizomes growing on the pond floor. The pond becomes sufficiently shallow
(2-5ft) for floating species and less suitable for rooted submerged plants.
Floating stage
The
floating plants are rooted in the mud, but some or all their leaves float on
the surface of the water. These include species like Nymphaea, Nelumbo Potamogeton and Echornia lilly. The
large and broad leaves of floating plants shade the water surface and
conditions become unsuitable for growth of submerged species which start
disappearing. The plants decay to form organic mud which makes the pond more
shallow yet (1-3 ft).
Reed swamp stage
The
pond is now invaded by emergent plants such as Phragmites (reed-grasses), Typha (cattail), and Zizania (wild rice) to form a
reed-swamp (in North American usage, this habitat is called a marsh). These
plants have creeping rhizomes which knit the mud together to produce large
quantities of leaf litter. This litter is resistant to decay and reed peat builds
up, accelerating the autogenic change. The surface of the pond is converted
into water-saturated marshy land.
Sedge-meadow stage Or Marginal stage
Successive
decreases in water level and changes in substratum help members of Cyperaceae and Graminae such as Carex, Juncus to establish
themselves. They form a mat of vegetation extending towards the centre of the
pond. The above water leaves transpire water to lower the water level further
and add additional leaf litter to the soil. Eventually the sedge peat
accumulates above the water level and soil is no longer totally waterlogged.
The habitat becomes suitable for invasion of herbs which grow luxuriantly and
bring further changes to the environment. Mesic conditions develop and marshy
vegetation begins to disappear.
Woodland stage
The
soil now remains drier for most of the year and becomes suitable for
development of wet woodland. It is invaded by shrubs and trees such as Salix
(willow), Alnus (alders), and Populus. These plants react upon the
habitat by producing shade, lower the water table still further by
transpiration, build up the soil, and lead to the accumulation of humus with
associated microorganisms. This type of wet woodland is also known as carr.
Climax stage
Finally
a self perpetuating climax community develops. It may be a forest (if
the climate is humid), grassland (if sub-humid environment), or a desert
in arid and semi-arid conditions. A
forest is characterized by presence of herbs, shrubs, mosses, shade-loving
plants and trees including decomposers.
The
overall changes taking place during development of successional communities are
building up of substratum, shallowing of water, addition of humus and minerals,
soil building and aeration of soil. As the water body fills in with sediment,
the area of open water decreases and the vegetation types moves inwards as the
water becomes shallower. Many of the above mentioned communities can be seen
growing together in a water body. The center is occupied by floating and
submerged plants with reeds nearer the shores.
What is xerach? Explain various
stages of xerach?
“ Ecological succession may be defined as on
orderly and progressive replacement of one community by another community until
reaching stable community occupies in that area”.
Or
“Successive
replacement of same habitat by different communities over a period of time in
particular area is called ecological succession.”
Xerach: when succession began in dry land
(and deserts, sand dunes, salt deserts, rock deserts etc.) are termed as
xerach. Various stages of development of
xerach are called xerosere.
When
succession started on bare area, is called as lithosere. When succession started from sand is called
psamosere. But when succession began on
the region or inter habitat between water and sand it is termed as mesorch.
Various stages of development of
xerach are as follows
•
Crustose lichen stage (Pioneer
stage)
•
Foliose and fruticose lichen stage
•
Moss stage
•
Herb stage
•
Shrub stage
•
Tree stage or Forest stage.
Crustose lichen stage (Pioneer
stage)
The
rock having extreme xeric condition.
The water and nutrients are extremely
deficient and there is direct exposure to sun, wind and extreme hot
temperature. In such condition crustose lichens enters in such area and become
pioneer. The thalli of crustose lichens
can adhere to the surface of rock and absorb moisture from atmosphere; &
colonize the bare surfaces of rocks first. The porpagules of these lichens are
brought by air from the surrounding areas.
These lichens produce acids which modifies the properties of the rock
leads to formation of thin film of
soil.When these lichens die their thalli are decomposed to add humus. This
promotes soil building and the environment becomes suitable for growth of
foliose and fruticose type of lichens.
Foliose and fruticose lichen stage
Foliose lichens have leaf-like thalli,
while the fruticose lichens are like
small bushes. They are attached to the substratum at one point only, They can
absorb and retain more water and are able to accumulate more dust particles.
Their dead remains are decomposed to humus which mixes with soil particles and
help building substratum and improving soil moisture contents further. This
layer of soil is formed get filled in to the depressions in the rocks and
crevices. It opens avenues (entry) for the growth of xerophytic mosses.
Moss stage
When
sufficient amount of soil accumulate in the crevices and depression in the rock
in which mosses begins to appear
xerophytic mosses such as black mosses, hair mosses, pristed mosses, etc. Their
rhizoids penetrate soil among the crevices, secrete acids and modifies the
rocks leads to formation of mat of soil. The bodies of mosses are rich in
organic and inorganic compounds. When these die they add these compounds to the
soil, increasing the fertility of the soil, greater water holding
capacity.
The
changing environment become suitable for the growth of herb plants.
Herb stage
By
the death of mosses the mat of soil is developed on which the germination of
seeds of various xerophytic herds is take place. Herbaceous weeds, mostly annuals such as
asters, evening primroses and milk weeds, invade the rock. Their roots
penetrate deep down, secrete acids and enhance the process of weathering. Leaf
litter and death of herbs add humus to the soil. Shading of soil results in
decrease in evaporation and there is a slight increase in temperature.
Xeric
conditions begin to change and biennial and perennial herbs and xeric grasses
such as Aristida, Festuca, and Poa, begin to inhabit. These climatic conditions
favor growth of bacterial and fungal populations, resulting in increase in
decomposition activity.
Shrub stage
On
the soil which is prepared by lichens, mosses and herb there is appearance of
xerophytic shrub is take place. The shrub make conditions unfavorable for herb
and shadow them. Due to this herbs
unable to compete with shrubs. The shrub also check evaporation of water from
soil and retard wind movement. Once a few bushes have become established, birds
invade the area and help disperse scrub seeds. The soil formation continues and
its moisture content increases. The environment becomes mesic (moderately
moist).
Tree stage or Forest stage or Climax
stage.
The
kind of tree species inhabiting the area depends upon the nature of the soil.
First species of the tree are relatively
xeric and have stunted growth. As
weathering process continues the soil deepness increases. Due to this trees grows in number and height
and become stable. Leaf litter and decaying roots weather the soil further and
add humus to it making the habitat more favorable for growth to trees. Xeric conditions are replaced by mesophyttic
trees which ultimately, develop in to forest or climax stage in future.
