Ecosystem

Ecosystem
• A functional unit of nature
where interactions of living
organisms with themselves
and with physical
environment takes place.
• The term ecosystem was
coined by Sir A.G. Tansley
(1935)
Shubhadeep Bhattacharjee/ Eureka Classes

Global Ecosystem
• The entire biosphere is
referred to as global
ecosystem, which consists of
several local ecosystems of
earth.
• The size of the ecosystem
can vary from a small pond
to a large forest or sea.

Classification of Ecosystems
Ecosystem
Natural Ecosystem
Terrestrial Ecosystem
Forest Grassland Desert
Aquatic Ecosystem
Fresh water Ecosystem Saltwater Ecosystem
Artificial Ecosystem
Crop Field
Aquarium

Stratification
• Vertical distribution of different species occupying different levels in
an ecosystem is called stratification.
1. Top trees.
2. Shrubs.
3. Herbs.
4. Grass.

Ecosystem: Structure & Function
i. The ecosystem consists of biotic and abiotic
components and their interaction with each other
results in a physical structure.
ii. The flow of energy takes place within these layers
of the ecosystem.
iii. The identification and enumeration of plants and
animal species in an ecosystem gives its species
composition.
iv. Stratification
v. The major functions of the ecosystem include:
a. productivity
b. Decomposition
c. Energy flow
d. Nutrient cycling

1. Productivity
• The rate of biomass production per unit area during a
given period of time is called productivity.
• It is measured in terms of weight (g𝑚−2
)/year or
energy (kcal 𝑚−2
)/year.
• It is used to compare productivity of different
ecosystems.

Primary productivity
• It is the amount of biomass produced per unit area in a given time
period by Plants during Photosynthesis
Aspects of
primary
productivity
Gross Primary
Productivity
(GPP)
Net Primary
Productivity
(NPP)

• Gross primary productivity (GPP): it is the rate of production of
organic matter during the process of photosynthesis in an ecosystem.
• Net primary productivity (NPP): it is the weight of the organic matter
stored by the producers in a unit area/ volume per unit time.
• NPP is equal to the rate of organic matter created by photosynthesis
minus the rate of respiration and other losses.
NPP= GPP-R

Primary productivity depends upon:
i. the plant species inhabiting a particular area
ii. Variety of environmental factors
iii. Availability of nutrients
iv. Photosynthetic capacity of the plants

Secondary productivity
• It is the rate of formation of new organic matter by consumers in a
given period of time.

2. Decomposition
• It is the process of breaking down of dead organic matter into smaller
organic and inorganic molecules by Decomposers (bacteria, fungi).
• Detritus: Raw materials of decomposition as dead plants, animals and
animal fecal matter is called detritus.
• Detrivores: Animals that feed on decaying organic matter (detritus).
Examples: earthworms, termites, snails etc.

Steps of decomposition:
1. Fragmentation of Detritus: It is the process of
breakdown of detritus into smaller particles. It is done
by detritivores.
2. Leaching: Soluble inorganic nutrients dissolve in
water and goes down to soil, get precipitated is called
leaching.
3. Catabolism: Decomposers (bacteria, fungi) release
enzymes to decompose detritus into simpler inorganic
compounds. Shubhadeep Bhattacharjee/ Eureka Classes

4. Humification: Simplified detritus converted to humus
a) Humus is a Dark, Amorphous substance.
b) Highly resistant to Microbial Action.
c) Undergoes Decomposition very Slowly.
d) Reservoir of nutrients (due to colloidal nature).
5. Mineralisation: Humus is degraded to releases inorganic substances
( CO2, H2O etc.) and nutrients (Ca2+, Mg2+,K + etc).

Factors affecting decomposition:
• Chemical composition - decomposition rate will be slow when
detritus is rich in lignin and chitin. The rate increases when detritus is
rich in nitrogen and water-soluble substances like sugars.
• Climatic conditions – warm and moist environment favour
decomposition. Low temperature and anaerobiosis inhibit
decomposition.

3. Energy flow
• Sun is the only source of energy for all ecosystems on earth.
• 50% of the incident solar radiation is photosynthetically active
radiation (PAR).
• Plants capture 2-10% of PAR and this small amount of radiation
sustains all life forms on earth.
• Unidirectional flow of energy- from sun to producers to the
consumers

Components of an energy flow system
Producers:
Green plants in the ecosystem which can trap solar energy to convert it
into chemical bond energy are called as producers.
Primary consumers:
Animals which feed directly on plants are called as primary consumers.
Secondary consumers:
Animals which depend on the primary consumers for their food are
called as secondary consumers.

Lindeman’s 10% Law
• At each step of food chain when food energy is transferred from one
trophic level to the next higher trophic level only about 10% of energy
is passed on to the next level.
• Given by Lindeman in 1942.

Food chain & Food web

Grazing food chain (GFC)
• Green Plants ------- Goat------ Man -------

Detritus food chain (DFC)
• Detritus ----- Decomposers (Saprophytes)

Trophic levels
• In an ecosystem, an organism occupy a specific place in the food
chain called trophic level.

Standing crop
• Each trophic level has a certain mass of living material at a particular
time is called standing crop.
• The standing crop is measured as the mass of living organisms
(biomass) or the number in a unit area.

Ecological pyramids
• The relation between producers and consumers in an ecosystem can
be graphically represented in the form of a pyramid called Ecological
pyramid
• Types of Ecological pyramids:
(i) Pyramid of Number
(II) Pyramid of biomass
(III) Pyramid of energy

Pyramid of number
• The relationship between producers and consumers in an ecosystem
can be represented in the form of a pyramid in terms of number
called Pyramid of number

Pyramid of biomass
can be represented in the form of a pyramid in terms of biomass
called pyramid of biomass.

Pyramid of energy
can be represented in the form of a pyramid in terms of flow of
energy called pyramid of energy.
• It is always upright.

Limitations of ecological pyramids
• It never takes into account the same species belonging to two or
more trophic levels. It assumes a simple food chain.
• It does not accommodate a food web.
• Saprophytes are never considered in an ecological pyramid even
though they play a crucial role in the ecosystem.

Ecological succession
• Climax Community:
Physical changes lead finally to a community that is in near
equilibrium with the environment and is called as the climax
community.
• Ecological succession:
The gradual and fairly predictable changes in the species
composition of a given area is called as ecological succession.

• Sere(s):
The entire sequence of communities that successively change in
a given area during succession are called as sere.
The individual communities are called as seral stage or seral
communities.
• Primary Succession:
the biotic succession which takes place in an area where no life
existed before is called as primary succession.
E.g. Bare rock/ newly created pond

• Secondary succession:
the biotic succession which takes place in an area where life
existed before but got destroyed due to some environmental reasons is
called as secondary succession

Succession of plants
• Hydrarch Succession:
The plant succession that takes place in a wet area or water body and
leads to a successional series from the hydric to the mesic conditions.

Xerarch succession
• The plant succession which takes place in a dry area and leads to a
successional series from xeric to mesic conditions is called as xerarch
succession.

• Pioneer species:
the species that invade a bare area are called pioneer species.
E.g., Lichens in a xerarch succession
• Process of ecological succession:
1. Nudation
2. Migration
3. Establishment of pioneer species
4. Aggregation
5. Intraspecific/ interspecific competition
6. Co-action
7. Reaction
8. Stabilization
9. Climax community/ Climax stage

4. Nutrient Cycling
• Standing crop: Each trophic level has a certain mass of living material
at a particular time, it is called as standing crop.
• Standing state: The amount of nutrients, such as carbon, nitrogen,
phosphorus, calcium, etc., present in the soil at any given time is
referred to as the standing state.
• Nutrient cycling/ Bio-geochemical cycling: The movement of nutrient
elements through the various components of the ecosystem is called
nutrient cycling.

Nutrient Cycle
Gaseous Cycle:
•The reservoir is the atmosphere.
•The nutrient occurs as gas or vapour.
•They are comparatively quick.
•E.g., Carbon/ Nitrogen Cycle
Sedimentary Cycle:
The reservoir is the earth crust.
The nutrient is non- gaseous.
They are quite slow.
E.g., Phosphorus/ Sulphur Cycle

a. Carbon Cycle

b. Phosphorus Cycle

Ecosystem Services
• The products of ecosystem processes are named as ecosystem
services.

Ecosystem

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