Ecological Succession.pptx

B.Sc. I, Sem. II, Paper III
PLANT ECOLOGY
Associate Professor, Dr. S. A. Gaikwad
Dept. of Botany
Vidnyan Mahavidyalaya, Sangola

Ecological succession
 The main causes of ecological succession include the biotic and climatic factors that
can destroy the populations of an area.
 Wind, fire, soil erosion and natural disasters include the climatic factors.
 Ecological succession is important for the growth and development of an ecosystem.
 It initiates colonization of new areas and recolonization of the areas that had been
destroyed due to certain biotic and climatic factors.
 Thus, the organisms can adapt to the changes and learn to survive in a changing
environment.

Concept of Ecological Succession:
 Ecological succession is the gradual process by which ecosystems change and develop over time.
 The time scale can be decades, or even millions of years after a mass extinction.
 Nothing remains the same and habitats are constantly changing.
 A series of plant communities occupies the fields in roughly predictable order while the habitat progressively
changes.
 Identically, newly formed marshlands or sand-dunes are colonized by regular successions of communities
even as the habitats change, most strikingly when moist soil develops on dry dunes.
 They may modify the habitat for plants and replace other animal communities in a colonizing dynamic of
their own.
 These facts of ecological succession have attracted ecologists principally because they suggest ordered
development.

Process of Ecological Succession: The ecological succession is a complex process
and it may take thousands of years. Frederic Clements in 1916 for the first time
proposed the sequential phases of an ecological succession. The process of
succession is completed through a series of sequential steps as given below…
1. Nudation: It is the first step in ecological succession. An area is exposed. It is
canvas for new painting. Nudation is the development of a bare area. The formation of
vegetation on bare area.
2. Invasion: It is the second step in ecological succession. Invasion is the successful
establishment of a species in the bare area. A new species reaches the newly created bare
area and they try to establish there. The process of invasion is completed in three steps:
a. Migration b. Ecesis c. Aggregation and Colonization

a. Migration: The process of dispersal of seeds, spores and other structures of
propagation of the species to bare area by wind, water, animals etc. is known as
migration.
b. Ecesis: Successful germination of propagules and their establishment in a bare area
is known as ecesis. The seeds or spores that reached the new area due to migration will
germinate, grow and reproduce. Only a few progenies will survive due to the harsh
environmental condition prevailing in the area.
c. Aggregation and Colonization : After ecesis, the individuals of the species increase
in number as the result of reproduction and they stay close to each other. The increase
in number of individuals by colonization and reproduction is known as aggregation.

3. Competition and Co-action:
Aggregation results in the increase of the number of species within a limited
space.
This results in competition between individuals for food and space.
Due to limited resources, species show both inter and intraspecific competition.
Individuals of a species affect each other’s life in various ways and this is called
co-action.
Competition and co-action results into the survival of fit individuals and the
elimination of unsuitable and weaker plants from the ecosystem.

4. Reaction:
 Reaction is most important stage in the ecological succession.
 It is the modification of the environment through the influence of living organism present on
it.
 Reaction cause change in soil, water, light and temperature of the area.
 Due to these modifications, present community become unstable for the existing
environmental conditions. Such communities will be quickly replaced by another community.
 The whole sequence of communities that replaces one another in the given area is called sere.
 The various communities contributing sere are called seral communities or seral stages.

5. Stabilization:
It is the final stage of the ecological succession.
The final or terminal community becomes more or less stabilized for a longer period of time.
This community can maintain itself in equilibrium with the climate of the area. This final
community is called the climax community or climax stage.
As compared to seral stage community, the climax community has larger size of individuals,
complex organization, complex food chains and food webs, more efficient energy use and
more nutrient conservation.
The climax community is not immediately replaced by other communities.
Climax community is determined by the climax of the region. Examples of the climax
community: Forest, Grassland, Coral Reef.

“Ecological succession is a series of changes that occur in an ecological community over time.”
Types of Ecological Succession: There are two types of ecological succession-
Primary Succession: Primary succession is the succession that starts in lifeless areas such as the regions
devoid of soil or the areas where the soil is unable to sustain life. When the planet was first formed there was
no soil on earth. The earth was only made up of rocks. These rocks were broken down by microorganisms
and eroded to form soil. The soil then becomes the foundation of plant life. These plants help in the survival
of different animals and progress from primary succession to the climax community. If this primary
ecosystem is destroyed, secondary succession takes place.
Secondary Succession: Secondary succession occurs when the primary ecosystem gets destroyed. For e.g., a
climax community gets destroyed by fire. It gets recolonized after the destruction. This is known as
secondary ecological succession. Small plants emerge first, followed by larger plants. The tall trees block the
sunlight and change the structure of the organisms below the canopy. Finally, the climax community arrives.

Seral Community: “A seral community is an intermediate stage of ecological succession
advancing towards the climax community.” There are seven different types of seres
A seral community is replaced by
the subsequent community.
It consists of simple food webs
and food chains. It exhibits a very
low degree of diversity.
The individuals are less in number
and the nutrients are also less.
Types of Seres Explanation
Hydrosere Succession in aquatic habitat.
Xerosere Succession in dry habitat.
Lithosere Succession on a bare rock surface.
Psammosere Succession initiating on sandy areas.
Halosere Succession starting in saline soil or water.
Senile Succession of microorganism on dead matter.
Eosere Development of vegetation in an era.

HYDROSERE (Hydrarch Succession)
Hydrosere is the primary succession which originates in aquatic environment. It occur in a area of fresh
water body such as lakes and ponds. It results in conversion aquatic community into a terrestrial
community. In time, area of open freshwater will naturally dry out, ultimately becoming woodland.
During this change, a successive seral developmental stages occurs. In large and very deep water body, a
noticeable change cannot easily be observed. However, in smaller water body such as a pond the
succession is easily recognizable. The various stages in a hydrosere are well studied in ponds, pools or
lakes. Hydrosere usually starts from a pond and A forest or a grassland will be the climax community.
Successive seral developmental changes in hydrosere takes place both in plants as well as in animals. A
sequence of various seral stages or seral communities of a hydrosere are as follows:-
1. Phytoplankton stage 4. Reed-swamp stage
2. Submerged stage 5. Sedge Meadow or Marsh Meadow stage
3. Floating stage 6. Woodland stage 7. Climax forest

HYDROSERE
1.Phytoplankton stage:
Hydrosere, originating in a pond, starts with the colonization by the pioneers like
phytoplanktons.
Phytoplankton's are the pioneer community.
In this initial stage phytoplanktons consisting of microscopic blue green algae, green
algae, diatoms and bacteria etc. are the first organism to colonize in 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 run off water and wave action and
form soil.
As soil builds up, the pond becomes shallower and further environmental changes follow.

HYDROSERE
2. Submerged stage:
As a result of death and decomposition of phytoplanktons, and their mixing
with slits, brought from the surrounding land by rain waters, a soft mud at the
bottom of pond develops. The new habitat which is now shallower and richer
in nutrients, and where light is available up to a certain depth becomes
suitable for the growth of rooted submerged hydrophytes like, Hydrilla,
Potamogeton, Vallisneria, Utricularia and Ceratophyllum. These plants bring
about further build up of the substratum as a result of their death and decay.
The water level also decrease making the pond more shallower.

HYDROSERE
3. Floating Stage:
Now the water depth is almost 2-5 feet. At this stage the pond is colonized by the
plant species which are rooted in mud with their large leaves floating on the water
surface. These are species of Nymphaea, Trapa, Monochoria etc. Some free floating
species as Azolla, Lemma, Wolffia, Pistia, Salvia etc., also become associated with
the rooted plants. The water level by now becomes very much decreased, making
the pond more swallower. The decomposing organic matter formed due to death of
these plants brings further build up of the substratum. Floating species sooner or
later disappear from the area.

HYDROSERE
4. Reed-swamp stage:
This stage is also called the "Amphibious Stage", as the plants of the
community are rooted but most parts of their shoots remain exposed to air.
Species of Typha, Sagittaria and Phragmites etc., are the chief plants of
this stage. Plants in this stage have well developed rhizomes and form
dense vegetation over the area and this will prevent the light penetration to
the lower portion. At this condition, the remaining rooted floating or free
floating or submerged plants of the previous seral stage disappears.

HYDROSERE
5. Sedge Meadow or Marsh Meadow stage:
Due to successive decrease in water level and further changes in the substratum,
species of some Cyperaceae and Gramineae, such as Carex, Juncus, Cyperus and
Eleocharis colonize the area. They form a mat like vegetation with the help of
their much-branched rhizomatous system. As a result of high rate of transpiration,
there is much rapid loss of water, and sooner or later, the mud is exposed to air.
Once the soil is exposed to the air, the nutrients such as ammonia, sulphides etc,
become oxidized to nitrates and sulphates. The condition in the area gradually
changes from marshy to mesic and marshy vegetation disappears gradually.

HYDROSERE
6. Woodland stage:
Disappearance of marshy vegetation, soil becomes drier for most of the
time and become suitable for development of wet woodland. This area is
now invaded by the terrestrial plants, which are some shrubs (Salix,
Cornus) and tress (Populus, Alnus). By this time of succession, there is
much accumulation of humus with rich flora of microorganism like
bacteria, fungi and other. Thus, mineralization of the soil favors the arrival
of new tree species in the area leading to the climax stages.

HYDROSERE
7. Forest Stage (Climax Stage):
Forest stage is the climax community in hydrarch succession. The woodland
community is invaded by a variety of large tree forms which soon develops into
climax community. The nature of the climax community (forest) is dependent
upon the climate of the region. In tropical climates with heavy rainfall, tropical
rain forest develops, whereas in temperate regions mixed forests of Ulmus, Acer
and Quercus develop. In region of moderate rainfall, there develop tropical
deciduous forest or monsoon forest.

Successive Changes In Animal Life During Hydrosere
There are also changes in the animal life, but these are not be as obvious as those in the plant communities. Thus,
with the ageing of a pond and the development of the marshes, the animal life also undergoes changes. These are as
fellow: - The protozoans like Paramecium, Amoeba, Euglena etc are the pioneers. When the planktonic growth
forms are very rich, other animal life form as blue gill fish, sun fish, largemouth bass etc., start appearing. Some
caddis flies are also found. In the next, submerged stage the caddis flies are replaced by other animals that may
creep over the submerged vegetation. Thus dragon flies, mayflies and some crustaceans inhibit the pond at this
stage. At the floating stage, the animal life is chiefly represented by Hydra spp., gill breathing snails, frog,
salamander diving beetles and other insects. Some turtles and snakes also appear. At the reed swap stages, the pond
becomes shallower, and the bottom starts to be exposed. The floating animals are replaced by different species of
mayflies and dragon flies, whose nymphs remain attached to submerged parts of the vegetation, and adults present
on the surface of emergent parts. Gill breathing animals like snails are replaced by lung breathers as Lymnea,
Physa etc . Among insects water scorpion, giant water bugs, scavengers beetles etc., are present at this stage.
Finally, at the woodland stage, under terrestrial condition most of the terrestrial forms of animal life appear in the
area

XEROSERE (Xerarch Succession)
Xerosere is a plant succession that is limited by the water availability. Succession takes place in Xeric or
dry habit like sand deserts, sand dunes or rocks where moisture is present at minimal amount is known
as Xerosere. Xeric succession commonly occurs on bare rock surfaces. Xerosere originate on bare rock
surface is known as Lithosere. The rocky habitat shows many extreme xeric conditions. As the rock is
directly exposed to sun, the temperature of rock surface goes very high. There is no water and nutrient
holding device on the exposed smooth surface of rock. In such a xeric habitat, only those plants can
survive which can resist the extreme drought. Like hydrosere, a xerosere also completes in a series of
several orderly steps; each seral stage being characterised by peculiar type of plant community and
reaction.
Seral Stages of Xerosere (Lithosere):
1) Crustose Lichens Stage. 2) Foliose Lichens Stage 3) Moss Stage
4) Herbs Stage 5) Shrubs Stage 6) Forest or Climax Stage

XEROSERE: Seral Stages of Xerosere (Lithosere)
1. Crustose Lichen Stage:
The pioneer colonizers on the bare rock are crustose lichens which occur on the rock surface in
the form of membranous crusts. The common species of crustose lichens of this stage are
Rhizocarpon, Rinodina, Lacidea and Lecanora etc. In dry periods the pioneers, though they
appear to be desiccated, remain alive. These plants grow only when water becomes available in
the habitat. These lichens migrate through their spores, soridia and propagules by wind and
water from the surrounding areas. The lichens secrete carbonic acid in excess. That acid is formed
when excess CO2 liberated in respiration combines with water. CO2 + H2O → H2CO3 (carbonic
acid). The carbonic acid reacts with the rocky materials and loosens the rock particles. The dead
organic matter of lichens becomes mixed with the small particles of rocks. The corroded rock
particles together with decaying lichens make the first thin layer of soil on the rock surface.
This process is very slow. These lichens are then replaced by foliose type of lichens.

2. Foliose Lichens Stage:
After accumulation of little soil and humus, the rock surface, previously occupied by crustose lichens,
now becomes covered with xeric foliose and fructicose lichens, e.g., Dermatocarpon, Parmelia,
Umbilicaria, etc. Foliose lichen have delicate large leaf like thalli which cover the rocks and
overshadow the pre-existing crustose lichen and cause their gradual death and decay. In this way more
and more humus accumulates. Foliose lichens can absorb and retain more water and able to accumulate
dust particles which help in the further build of the substratum. They make the soil acidic. The
weathering of rocks and its mixing with humus results into the development of a fine thin soil layer on
the rock surface which consists of rock particles, remains of lichens, dust particles and moisture. Thus
there is a change in the habitat. They also secrete carbonic acid which further pulverizes or loosens the
rocks into small particles. The water retaining capacity of the habitat increases with the further
accumulation of soil particles and humus. Gradually the conditions become less favourable for the
existing foliose and fructicose lichens.

3. Moss Stage:
The development of thin soil layer on rock surface, especially in the cervices favours the
growth of some xerophytic mosses as species of Polytrichum, Tortula and Grimmia.
Xerophytic mosses grow and become dominant. These plants usually grow in the crevices and
depressions of the rocks. The xerophytic mosses develop rhizoids which penetrate deep into
the rocky soil secrets acids and corrode the rocks . They cover the previous lichens and
successfully compete with them for water and mineral nutrients. The decaying older parts of
mosses form a thick mat over the rock surface. As this mat becomes more thick, it increase the
water holding capacity of soil. Mosses are rich in organic and inorganic compounds. Due to
their death and decay they add organic and inorganic matter in the soil and increasing the
fertility of the soil. The thickness of the soil layer is now increased. Thus the habitat becomes
relatively more wet. Now the next seral community may replace the moss community.

4. Herbs Stage:
When the soil increases in thickness, the herbaceous vegetation, which consists
mainly of annual and perennial herbs, develops very quickly. Increased moisture
content of the soil favours the growth of herbs. The roots of these plants penetrate
down almost to the level of unpulverized rock where they secrete acids and accelerate
the process of rock disintegration. In this way the thickness of soil on the rock
surface increases to a considerable extent. Decaying leaves stems, roots and other
parts of the plants become deposited on the soil surface in the form of humus This
further increases the water holding capacity of the soil. Thus, habitat changes with
decreasing xeric condition. Some xerophytes rooted grasses such as Aristida,
Festuca, and Poa etc., begin to inhibits, which in turns are replaced by shrubs.

5. Shrub Stage:
Due to much accumulation of soil the habitat becomes suitable for the shrubs which start
migrating in the area. These are the species of Rhus, Phytocarpus etc. They overshadow
the herbaceous vegetation. The soil is further enriched by this dense shrubby growth.
Shrubs are larger and their roots reach greater depth causing further cracks in the rock
substratum. Roots of shrubs also reach the surface оf unpulverized rocks and corrode
sufficient quantity of rock particles which make the soil more massive. Decaying leaves,
twigs and roots of these shrubs also enrich the soil with humus. These important reactions
bring about such conditions in the habitat as are most suited to the trees rather than to
shrubs and herbs. The process of soil formation continues. These in turn are finally
replaced by tress which make up the climax community.

6. Forest or Climax stage:
With the establishment of shrubs, more and more soil is formed and environment
becomes increasingly humid. This favours the growth of woody trees. In the
beginning, trees show stunted growth and are sparsely placed. Some xerophytes
tree species invade the area. Further weathering of rocks and increasing humus
content of the soil favour the arrival of more trees and vegetation finally becomes
mesophytic. Finally a climax forest community is established. The climax
community is the last aggregation in the successional series. These forest
community is the climax stage for this region. Climax community is controlled
by climate of an area and is known as climatic climax.

Changes In Animal life During Xerosere (Lithosere)
There occur successive changes in the animal life during the xerosere succession. Associated
with the lichens, the pioneer are a few mites. Fauna is sparse in terms of species composition.
There are few ants and few spiders present in the cracks and cervices of rocks. The mites
become more varied in terms of species and small spiders, springtails as well as tradigrades
become associated with the secondary community of mosses. At later stage of succession
when grasses start developing, there is quantitative and qualitative increase in the fauna.
Nematodes and larval insects, ants, spiders and mites appear in this new environment. With
the development of forest climax community, there develop a rich fauna consisting of
invertebrates as well as vertebrates. These include slugs, snails, millipedes, centipedes, ants,
sow bugs, squirrels, mammals like fox, chipmunk, mouse and mole, birds like grouse and
flycatcher, reptiles like snakes turtles etc. and amphibians such as salamanders and frogs.

Difference between Hydrosere & Xerosere

Ecological Succession.pptx

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