environmental science and ecosystem

Environmental Science
LIVE & LET LIVE

What is Environmental
Science?
The study of how humans interact with
their environment
Our environment is everything that
surrounds us, both natural and man-made.

Environment: the total of our
surroundings
• All the things around us with which
we interact:
• Living things
• Animals, plants, forests, fungi, etc.
• Nonliving things
• Oceans, clouds, soil, rocks
• Our built environment
• Buildings, human-created living centers
• Social relationships and institutions

SEGMENTS OF ENVIRONMENT
• Atmosphere – it is composed of several
distinct layers such as troposphere,
stratosphere, mesosphere and ionosphere.
• Hydrosphere – Water – Ocean
• Lithosphere – Solid part of the Earth crust.
– The crust includes minerals, soil and rock.
– Largest volume of Earth’s interior – Mantle.
• Biosphere – It is the part of the earth which
includes Air, Land, Water, Rock within which
life occurs.

ENVIRONMENTAL ETHICS
• It is our moral obligation to future generations to
provide them clean environment, full of natural
resources in good conditions.
• All organisms are valuable but human are really
matter becoz they are capable to improve the
earths environ. And make it better and sustainable
place, both for themselves and for other organisms.
• The Env. Ethics evaluate the relationships, rules,
principles b/w the humans and their env. to lead a
better life at present and to provide best env. to
future generations.

ENVIRONMENTAL VALUES
• In terms of utility, the env. has a great value to
individual as well as to a community. The natural
resources provide individuals life supporting
amenities, economic benefits, etc.,
• Millions of beautiful and intriguing species populate
the earth and help sustain a habitable env.
• The earth has a rich diversity of flora and fauna
which altogether make the earth’s env. more
valuable.

ENVIRONMENTAL KNOWLEDGE
• It is essentil
 To identify the env. problems
 To know the root cause of the problems
 To know the intensity and effect of the env. problems
To attain a knowledge and understand the diff.
processes of ecological systems which in turn
helps to solve the problems.
To develop an appropriate technology which will
advocate safe, creative, environmentally sound
and suitable solutions to the env. problems.

Objectives of Environmental Education
• Participation - working towards stainable
development
• Knowledge
• Values - to develop an ethic of respect and
responsibility for the environment.
• Skills - acquire skill to identify the env. Problems –
work with others to resolve, minimize and prevent them.
• Awareness - create awareness and promoting env.
Friendly life style
• R&D Activities -
• Environmental related Laws.
• To adopt technology without affecting the environment.

Living things
+
Nonliving things
= ECOSYSTEM

• Environmental Studies – Impact on the society and
involvement of the society in combating the causes
of env. Degradation.
• Environmental Science – Systematic study of biotic
and abiotic inter relationship.
• Env. Engg. - causes and effects of pollutants
• Env. Chemistry - study of various chemical
phenomena taking place in diff. segment of env.
• Env. And Ecology – interdisciplinary in nature and
biology, chemistry, geography, agri, etc.,

FORMAL EDUCATION
• Awareness programme through children and youth -
- they create new idea
• Inter disciplinary approach adopted
– To achieve sustain
• Hands on experience
– Education must be imparted not only through books but
also through first hand experience in field activities.

NON FORMAL EDUCATION
• It organises extracurricular activities like
eco development camp,
posters,
competition,
exhibition,
seminar,
club activities, mobile exhibition
• Other activities like tree plantation, fencing,
cleaning water bodies
• Education through arts, crafts, street plays,
Advertisement, etc.,

• Considering the env. In its total ability including nature,
artificial, ecological, etc.,
• Considering the people at various level and their
involvement.
• Considering education with multi disciplinary approach
• Examine major env. Issues.
• Develop problem solving skills
• Promote active participation at various levels.
• Discover symptoms and root causes of env. degradation.

Awareness through
seminar/conf/Posters/short film/Advt.
Env. Edu. Through children/coll.students
Env. Info. System (EIS)
World Env. Day 5th June
Training Programmes & R&D

• Ecosystem - living things in a given area, non-living
chemical and physical factors of their environment,
linked together through nutrient cycle and energy flow
Types of Ecosystem
Natural Artificial/Man-made
Terrestrial
(Forest, Grass
land, Desert)
Aquatic
Marine Fresh water
Lotic -river, stream or spring. Lentic -lake, pond or swamp.

Population
Population
+ Population
COMMUNITY

Name the three members in
every community.
Producers
Consumers
Decomposers

All energy in a
food web comes
from the…

What makes ecosystems different?
Amount of water
Amount of sunlight
Type of soil
1
2
3

Ecology:
Study of the distribution and abundance of organisms, the flows of energy
and materials between abiotic and biotic components of ecosystems.
Ecosystem Structure:
The living components of an ecosystem /
The roles of organisms in an ecosystem:
• Producer (autotrophy): make food; plants, algae
• Consumer (heterotrophy): eat other organisms
• Decomposer: eat dead organic matter; bacteria and fungi

Classes of Consumers
Herbivore – primary consumer – eats plants
Carnivores – secondary – meat eaters; eat herbivores
Omnivores – eat plants/animals.

What causes ecosystems to change?
Natural causes:
Drought
Disease
Fire
Overpopulation
3
2
1
4

What causes ecosystems to change?
Changes caused by humans:
Water pollution
Air pollution
Land pollution
Construction
1
2
3
4

How can humans help to prevent
changes in ecosystems?
Use resources wisely
1
Laws that control pollution
Clean up litter
Keep rivers and lakes clean
2
3
4

Ecosystems:
Fundamental Characteristics
ABIOTIC components
• Solar energy provides practically all the energy
for ecosystems.
• Inorganic substances, e.g., sulfur, boron, tend to
cycle through ecosystems.
• Organic compounds, such as proteins,
carbohydrates, lipids, and other complex
molecules, form a link between biotic and abiotic
components of the system.

Ecosystems:
Fundamental Characteristics
BIOTIC components
• The biotic components of an ecosystem can be
classified according to their mode of energy
acquisition.
• In this type of classification, there are:
• Autotrophs and Heterotrophs
• Organisms that produce their own food from an
energy source, such as the sun, and inorganic
compounds.
• Organisms that consume other organisms as a
food source.

Trophic level: All the organisms that
are the same number of food-chain steps
from the primary source of energy

Trophic Levels
• A trophic level is the position occupied by an
organism in a food chain.
• Trophic levels can be analyzed on an energy
pyramid.
• Producers are found at the base of the pyramid and
compromise the first trophic level.
• Primary consumers make up the second trophic
level.
• Secondary consumers make up the third trophic
level.
• Finally tertiary consumers make up the top trophic
level.

Trophic Levels Found on an
Energy Pyramid
• The greatest amount of energy is found at the base of
the pyramid.
• The least amount of energy is found at top of the
pyramid.
Source: corpuschristiisd.org/user_files/91702/Ecosystem.ppt

FOREST ECOSYSTEM
(TERRESTRIAL ECOSYSTEM)
 A forest is an area with a high density of trees.
 World’s total land area is 13,076 million
hectares
 Of which total forests account for about 31% of the
world’s land area.
 In India, the forest cover is roughly 19% of the
total land area.
 The forest ecosystems are of great concern
from the environmental point of view.

FOREST ECOSYSTEM
(TERRESTRIAL ECOSYSTEM)
 It provides numerous environmental services
like;
• Nutrient cycling,
• Maintaining biodiversity
• Providing wildlife habitat
• Regulating stream flow
• Storing water
• Reducing flooding
• Preventing soil erosion
• Reclaiming degraded land & many more….

Structure and Function of
FOREST ECOSYSTEM
Biotic components
I. Producer Organisms
In a forest, the producers are mainly trees.
Trees are of different kinds depending upon the type of
forest developed in that climate.
Apart from trees, climbers, epiphytes, shrubs and ground
vegetation.
Dominant species of trees in major types of forest
ecosystems are:
Tectona grandis, Acer, Betula, Picea, Pine, Cedrus.

Structure and Function of
FOREST ECOSYSTEM
Biotic components - Consumers
In a forest, consumers are of three main types;
a) Primary Consumers
These are Herbivores which feed directly on producers. Eg:
Ants, Beetles, Bugs, spiders etc. feeding on tree leaves.
Larger animals such as Elephants, Deer, giraffe etc. grazing on
shoots and/or fruits of trees.
b) Secondary Consumers
These are carnivores and feed on primary consumers.
• Eg: Birds, Lizards, Frogs, Snakes and Foxes.
c) Tertiary Consumers
These are secondary carnivores and feed on secondary consumers
These include top carnivores like Lion, Tiger.

Biotic components – Decomposers
These include wide variety of saprotrophic micro-organism
like;
 Bacteria
 Fungi
 Actinomycetes (Streptomyces).
They attract the dead or decayed bodies of organisms &
thus decomposition takes place.
Therefore, nutrients are released for reuse.

II. Abiotic components
• These include basic inorganic & organic
compounds present in the soil &
atmosphere.
• In addition dead organic debris is also
found littered in forests.

Structure and functions of
Grassland Ecosystems
I. Biotic components
• Producer Organisms
• In grassland, producers are mainly grasses; though, a
few herbs & shrubs also contribute to primary production
of biomass.
• Some of the most common species of grasses are:
– Brachiaria sp., Cynodon sp., Desmodium sp.,

Structure and functions of Grassland Ecosystems
I. Biotic components - Consumers
a) Primary Consumers
• The primary consumers are herbivores feeding directly on
grasses. These are grazing animals such as
• Cows, Buffaloes, Sheep, Goats, Deer, Rabbits etc.
• Besides them, numerous species of insects, termites, etc
are also present.
b) Secondary Consumers
• These are carnivores that feed on primary consumers
(Herbivores)
• These include;-Frogs, Snakes, Lizards, Birds, Foxes,
Jackals etc.
c) Tertiary Consumers
• These include hawks etc. which feed on secondary
consumers.

I. Biotic components – Decomposers
 These include wide variety of saprotrophic
micro- organism like: Bacteria; Fungi;
Actinomycetes
 They attract the dead or decayed bodies of
organisms & thus decomposition takes place.
 Therefore, nutrients are released for reuse by
producers.

 These include basic inorganic & organic compounds
present in the soil & aerial environment.
 The essential elements like C, H, N, O, P, S etc. are
supplied by water, nitrogen, nitrates, sulphates,
phosphates present in soil & atmosphere.

DESERT ECOSYSTEM
• A desert is a landscape or region that receives almost
no precipitation.
• Deserts are defined as areas with an average annual
precipitation of less than 250 millimeters per year.
• It occupies about 17% of the earth’s surface.
• Deserts are characterized by hot days & cold nights.
• The deserts of the world are mainly located in the
South- western United States, Mexico, North
America, Asia (Thar, Gobi, Tibet) & west Asia.
• Deserts are characterized by scanty flora & fauna.
• Soils of deserts often have abundant nutrients but little or
no organic matter.

1) Producer Organisms
• In a desert, producers are mainly shrubs/bushes; some grasses & a
few trees.
• Dominant plant species include: Succulents (water -
retaining plants adapted to arid climate or soil conditions) & hardy
grasses.
2) Consumer Organisms
• These include animals such as insects, reptiles which are capable of
living in xeric conditions
• Besides some birds & mammalians like camel etc are also found.
3) Decomposers
• Due to poor vegetation with very low amount of dead organic matter,
decomposers are poor in desert ecosystem.
• The common decomposers are some bacteria & fungi, most of which
are thermophillic.

• Due to high temperature & very low
rainfall, the organic substances are poorly
present in the soil.

Freshwater Ecosystems
1) Producer Organisms
• It includes submerged, free floating and amphibious macrophytes
(like; Hydrilla, Wolfia, Azolla, Typha etc.) and minute floating and
suspended lower phytoplanktons (like; Ulothrix, Spirogyra,
Oedogonium etc.)
2) Consumer Organisms
• a) Primary consumers: These are zooplanktons (ciliates,
flagellates, other protozoan, small crustaceans) and benthos.
• b) Secondary consumers: These are carnivores like insects and
fishes feeding on herbivores
• c) Tertiary consumers: These are the large fishes feeding on
small fishes.
3) Decomposers Micro – organisms like bacteria, fungi and
actinomyctes.

Freshwater Ecosystems
II. Abiotic component
• These are the inorganic as well as organic substances
present in the bottom soil or dissolved in water. In addition,
to the minerals, some dead organic matter is also present.

Marine or Ocean Ecosystem
• Marine ecosystems are among the Earth's aquatic
ecosystems. They include: Oceans,
Estuaries and Lagoons, Mangroves and Coral reefs,
the Deep sea and the Sea floor.
• These are the gigantic reservoirs of water covering
approximately 71% of the Earth's surface (an area of some
361 million square kilometers).
• These ecosystems are different from freshwater
ecosystem mainly because of its salty water.

1) Producers It includes phytoplanktons (diatoms,
dinoflagillates), large seaweeds (mainly algae like
chlorophyceae, phaeophyceae & rhodophyceae; angiosperms
like Ruppia, Zostera, posidonia ), and mangrove vegetation
(like Rhizophora, Carapa etc.)
2) Consumers
• a) Primary consumers: These are herbivores and feed directly
on producers (Crustaceans, Mollusks, fish etc.)
• b) Secondary consumers: These are carnivorous fishes
(Herring, Mackerel)
• c) Tertiary consumers: These are top carnivorous fishes (Cod,
Haddock, etc.)
3) Decomposers These are micro – organisms like bacteria,
fungi

• High Na, Ca, Mg and K salt concentration, variable
dissolved oxygen content, light & temperature make a
unique physiochemical conditions in marine water.
•

Biological Productivity
• The rate of biomass production
/ unit area / unit time is called Productivity.
• The total amount of org.matter on any
particular ecosystem is called Biomass.
• The change in Biomass over a given period
of time is called Net Production.
• There are 2 kinds of production
– Primary Production
– Secondary Production

Primary Production
rate of biomass production of a community
The process is carried out by autotrophs by forming
sugar from sunlight, CO2 & H2O through
photosynthesis. The energy left after respiration is net
primary production.
hv
6CO2 + 6H2O C6H12O6 + 6O2 (Photosythesis)
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
(Respiration)

Secondary Production
– The production by heterotrophs from the
primary production is called SP.
– Defined as the rate of energy transferred and
stored at consumer level over a period of
time.
– Heterotrophs which cannot make their own
food but must feed on other living organisms.

Food Chains
Transfer of energy and nutrients from one
feeding group of organism to another
• The producers, consumers, and
decomposers of each ecosystem make up
a food chain.
• There are many food chains in an
ecosystem.
• Food chains show where energy is
transferred and not who eats who.

Types of Food Chains
• Grazing food chain
Plants
Herbivores
(cattle, elephant, etc.)
Prim.Carnivores
(tigers, lions, snakes, etc.)
Second.Carnivores (hawk, owl, fox, etc.)

Types of Food Chains
• Detritus Food Chain - The org. waste and
dead matter derived from grazing food chains
are called detritus.
Dead Organic Materials (Decomposing org.matter)
Detrivores (Algae, Fungi, Bacteria, earthworms, etc.,)
Chemical Energy -- Simpler Org. Compds
CO2 + H2O

Biomagnification
• Biological Magnification
– Ecological Balance :
• Maintaining and Regulating the population size
- In addition, at each trophic level, the concn.
of food chains keep on increasing,

Food Webs
In ecosystems, some consumers feed on a
single species, but most consumers have
multiple food sources.
Hawk eats both mouse and snake.
In this way, individual food chain becomes inter-connected
to form a food web.

Food Webs
• All the food chains in an area make up the food web of the area.
• Maintaining the stability of an eco system

ENERGY FLOW IN ECOSYSTEM
• All organisms must obtain a supply of energy and nutrients
from their environment in order to survive.
• The transformations of energy in an ecosystem begin first with
the input of energy from the sun.
• Because, it is the first step in the production of energy for
living things, it is called “Primary production”.
• Photosynthesis -- Chemical reaction where green plants use
water & carbon dioxide to store the sun’s energy in glucose.
• ENERGY is stored in glucose. Glucose is stored as starch in
plants
• The energy contained within producers and consumers is
ultimately passed to the decomposers that are responsible for
the constant recycling of nutrients.

ENERGY FLOW IN ECOSYSTEM
• Thus, there is a one-way flow of energy through the
biotic community and a cycling of nutrients between the
biotic and abiotic components of the ecosystem
• Energy flow cannot occur in reverse direction.
• The amount of energy decreases with successive trophic
levels.
• Only About 1% of energy from the sun is used by green
plants & rest remains unutilized.
• Similarly, there is loss of energy in each trophic level.
• The transfer of food energy between the organisms in an
ecosystem can be tracked by constructing food chains,
food webs, pyramids of numbers, biomass, etc.,

NUTRIENT CYCLES
• Nutrient cycles involve storage and
transfer of nutrients through different
components of the ecosystem, so that the
nutrients are repeatedly used.
• The cyclic movements of chemical
elements of the biosphere between the
organisms and environment are referred
as “BIOGEOCHEMICAL CYCLES”

BIOGEOCHEMICAL CYCLES
• It involves biological, geological and chemical
systems and all are interlinked through a cyclic
chain.
• It is the complete pathway that a chemical
element flows from the atmosphere, water, rock
or soil to the living organisms and again back to
the atmosphere, water, rock or soil.
• The return of chemical elements from living
organisms to abiotic component is called
Mineralization.

PLANTS
ANIMALS
MICRO-ORGANISMS
NUTRIENTS
CYCLE OF NUTRIENTS

• There are 4 different biochemical cycles
– Hydrological cycle (water)
– Carbon cycle
– Nitrogen cycle
– Phosphorous cycle

HYDROLOGIC CYCLE
• In this cycle, fresh water evaporates and
condenses on the earth. Oceans are the
main source of evaporated water, which
leaves behind salts.
• Water also evaporates from fresh water
bodies, from land and plants.

HYDROLOGIC CYCLE
The steps involved in hydrologic cycles are
– evaporation
– condensation
– infiltration
– runoff
– precipitation

CARBON CYCLE
• Carbon enters plants as CO2
– Bacteria process carbon in a fashion that allows it to
be recycled.
– Obtain energy from the molecules, and convert
carbohydrates to carbon dioxide as a result of
respiration.
• Photosynthesis removes carbon from the abiotic
environment (fixes carbon into organic molecules)
• Carbon moves through food chain through consumption
of one organisms by another
• Cellular respiration, combustion, and erosion of
limestone return carbon to the atmosphere, water and
abiotic environment.

RESPIRATION
AIR CO2 PLANTS
DEATH FOOD
RESPIRATION ANIMAL
BURNING
COMBUSTION
WOOD FOSSIL FUEL
Fig.2.11.2 Carbon Cycle
The source of atmospheric carbon dioxide is variable but only plants can utilize atmospheric
carbon directly

NITROGEN CYCLE
• Nitrogen is crucial for all organisms
– Nucleic acids
– Proteins
– Chlorophyll
• Nitrogen- 78% in Atmosphere
• N2 is very stable and must be broken apart by
organisms, combined with other atoms into a
usable form.
• The process of entering atm. Nitrogen into
the organism and again back to the
environment completes the Nitrogen cycle.

1) Nitrogen Fixation NF can be carried out by symbiotic N fixer and
non-symbiotic N fixer and other natural as well as industrial process.
– Conversion of N2 → NH3
• Symbiotic bacteria, associated with roots of legumes and flowering
plants. eg. Rhizobium which convert N into the organic nitrogen for
their own cells. when these organisms die or leave wastes certain
other bacteria and fungi return the N to the soils and atm.
• Non-symbiotic N fixers are both aerobic and anaerobic bacteria as
well as cyano bacteria. These occur in soil, marine and fresh water.
• Lightening storms convert atm.N into nitrates and reaches the soil
through rain water. They can also be converted to ammonia by
denitrifying bacteria.

2) Nitrification
• Conversion of NH3 → NO3
• Nitrosomonas convert ammonia to nitrite. Nitrobactor converts
nitrite to nitrate. This nitrate is taken up by higher plants and
convert it into protein and nucleic acids.
3) Eutrophication
• Discharge of excess qty of nitrogeneous compds into rivers and
lakes can result excessive growth of algae and macrophytic plants.
4) Ammonification
• Amino acids and nucleotides are broken down into
NH3 or NH4
5) Denitrification
• The reduction of NO3 to N2 .
• Denitrifying bacteria release gaseous nitrogen back in to the
atmosphere

Consumers
Detritus
Atmospheric Nitrogen
Denitrification
Pseudomonas
Plants
Ammonification
Heterotrophs
Litter fall
Uptake
Soil nitrite Nitrosomonas Nitrobacter Soil nitrate
Wet & dry
deposition
Fig.2.11.1 Nitrogen Cycle
Nitrogen fixation by free
living & symbiotic
microbes.
Nitrification
Soil ammonia

PHOSPHOROUS CYCLE
• The only cycle that does not have a gaseous state
• Inorganic phosphate PO4
3- is released from rocks and
sediments through the action of erosion.
• Soil PO4
3- is absorbed by plants and incorporated into nucleic
acids, phospholipids and ATP (adenosine triphosphate).
• Animals obtain most of their PO4
3- by consumption of other
animals and from water.
• PO4
3- is released to the soil again by decomposers.
• Dissolved PO4
3- gets absorbed by algae and aquatic plants
• Decomposers break down waste and returns PO4
3- to
sediments on the seabed.

Parental Rock
3- in soil.
Soluble PO4
(orthophosphates)
Bacteria
Insoluble phosphate
Plants (Roots)
Animals Death
Bone/ Teeth
Decomposition
Bacterial
Decomposition
Fig.2.11.3 Phosphorus Cycle

Oxygen Cycle
Oxygen is the most import. element in our
life.
About 21% of Oxygen is present in the atm.
As free O2.
Plants and animals can take the free O2 from
the atm. through a process called respiration,
and it release CO2 and water into the atm.

Oxygen Cycle
CO2
CO2
PLANTS & ANIMALS ATMOSPHERE
O2
O2

ECOLOGICAL PYRAMIDS
• An”Ecological pyramid” is a graphical representation
that shows the relative amounts of energy or matter
contained within each tropic level in a food chain or
food web.
• An ecological pyramid shows the relationship
between producers and consumers at different
tropic levels in an ecosystem
• There are three ecological pyramids
– Pyramid of Numbers
– Pyramid of Biomass
– Pyramid of Energy

Pyramid of Number
• It is the graphical representation of the no.
of individuals in various trophic levels of
food chain / unit area at any given time.

• In Gross land, Pond eco systems
Producers > Herbivores > Carnivores
– Hence the pyramid is upright
• When the ecosystems contain lesser no.
of producers than those of consumers, the
apex of the pyramid is directed
downwards. This types of pyramids are
called Inverted Pyramids.

Examples of Inverted Pyramid
• Tree Ecosystem
– A single tree harbors many fruit eating birds
(Prim.consumer) and these birds in their turn,
host numerous parasites. (sec.consumer)

Pyramid of Biomass
• It represents the total dry mass (in grams per square
meter of area) of all the organisms in each tropic level
at a particular time.
Inverted Pyramid

Pyramid of Energy
• It represents the rate of energy flow and/or productivity
at successive tropic levels. The pyramids of energy
are always upright.
Ener
gy

Amount of Energy decreases from
Producers
PC
SC
TC
Since the flow of energy is unidirectional, the pyramid energy is UPRIGHT

Ecological Succession
• Natural, gradual changes in the biotic community
towards a stable or climax condition;
• The changes are progressive and predictable.
• The occurrence of sequence of communities over a
period of time in the same area is termed as ES.
• Based on the nature of habitat: primary or secondary.
– Primary – begins in a place without soil
– Secondary – where soil already exists
• Based on the types of organisms.
– Autotrophic Succession
– Heterotrophic Succession

Pioneer species
• A group of organisms, such as lichens, found in
the primary stage of succession.

Climax community
• A community that has reached a
stable stage of ecological
succession

Based on Nature of habitat:
Primary Succession
• PS is defined as the initial establishment and
development of an ecosystem which occurs on a
site previously unoccupied by living organism.
• The organisms that establish their first are called
“Pioneer organisms” / Primary colonizers.
• Simple plants first.
• Gradual arrival of more complicated and larger
plants as the habitat changes
• Unfavorable for life at first.
• Ends with a “climax community” – ecosystem stays
constant, provided there are no changes in abiotic
influences.

Secondary Succession
• Community development in the previously occupied
areas is replaced by other community.
• If successions starts on an area, previously colonized,
and the soil is organically enriched, it is known as SS.
• SS is defined as the reestablishment of a new
ecosystem at a site where community was existing
earlier but disrupted by natural or artificial means like
storm, fire, flood or human activities.
• E.g., loss of trees after disease, Fire or wind,
deforestation etc.
• More rapid than primary succession.

Primary Vs Secondary
• No soil.
• Pioneer species.
• Weathering &
decomposition
• End = Climax
community.
• Soil already exists.
• Seeds have suitable
soil conditions.
• Occurs much faster.
• Climax community.

Based on types of Organisms
• Autotrophic Succession: It begins in a
predominantly org. env. characterized by
early and continued dominance of
Autotrophic Organisms like green plants.
• Heterotrophic Succession: It begins in a
predominantly org. env. characterized by
early dominance of Heterotrophs like
bacteria, fungi and animals.

Process of Succession
1. Nudation
2. Invasion
3. Migration
4. Colonisation
5. Ecesis
6. Aggregation
7. Competition and reaction
8. Climax or stabilization

1. Nudation: The process of formation of a
bare area is known as Nudation
• Caution
– Industrial / Agricultural – Manmade
– Climatic Change
– Biotic disturbances – Natural
• Landslides
• Floods

2. Invasion: The process of successful
establishment of new species in the bare
area is known as Invasion
3. Migration: The process of movement of
organisms in to the bare area is known as
Migration.
The seeds, spores of the species invade
(enter by force) to the bare area by the
agents such as Air and Water.

4. Colonisation: Occupation of the bare area
by first or pioneer community is called
colonisation
5. Ecesis: After reaching the bare area, the
new species starts to establish themselves in
it. Establishment of pioneer community is
called Ecesis. Such pioneer reacts with the
medium like soil or water and establishes
themselves.

6. Aggregation: The final stage of Invasion by a
Pioneer group is called Aggregation. The
species which has successfully settled in the
new area, reproduce and aggregate into large
population in the new area.
7. Competition and Reaction: After
establishment, various species compete among
themselves for space, light and nutrients.
Communities which cannot withstand during
competition, are replaced by other communities
till a climax community is established.

8. Stabilization: This is the final stage in the
process of ecological succession. The climax
community becomes more or less stabilized for
a long period of time. It can maintain itself in
equilibrium with the climate of that area.

environmental science and ecosystem

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