CHAPTER : 14 ECOSYSTEM
ENVIRONMENT
It is the physical and the biological world where we live.
OR
It is the surrounding where we live.
ECOSYSTEM
 It is the structural and functional unit of biosphere.
 The term ecosystem was proposed by A.G. Tansley in 1935.
 An ecosystem is the basic functional ecological unit in which living
organisms interact among themselves and with their surrounding physical
environment.
TYPES OF ECOSYSTEMS
NATURAL ECOSYSTEM
AQUATIC
ECOSYSTEM
FRESH WATER
ECOSYSTEM(ponds,
rivers,streams,springs,lak
es etc. )
TERRESTRIAL
ECOSYSTEM(
desert, grassland,
forest etc.)
MARINE WATER
ECOSYSTEM (ocean, sea,
wetlands, estuaries) etc.
ARTIFICIAL
ECOSYSTEMOR MANMADE ECOSYSTEM ( park,
zoo, botanical garden,
aquarium, crop field etc.)
COMPONENTS OF ECOSYSTEM
There are two main components of the ecosystem:
(A) BIOTIC COMPONENTS :-The living components of the environment. Example.plants, animals, man, microbes etc.
(B) ABIOTIC COMPONENTS :-The non-living components of the environment.
Example :-sunlight, temperature , rainfall etc.
A. BIOTIC COMPONENTS
(i) Producers (Autotrophs):The organisms which can produce their own food
by photosynthesis. They are of two types :
(a) Photoautotrophs : The organisms that use light energy and inorganic carbon
to produce organic materials.Example : Blue green algae.
(b) Chemoautotrophs :The microbes that use light energy and organic chemical
substances as sources of energy and organic compounds as the main source of
carbon. Example :Nitrobacter , Nitrococcus etc.
(ii)Consumers: The organisms which depend upon the producers for food either
directly or indirectly.There are 3 types of consumers :
a. Herbivores/ Primary Consumers : The plant eating animals. Ex.- cow ,
goat, etc.
b.Carnivores/ Secondary Consumers :The flesh eating animals. Ex.lion, tiger etc.
c. Top Carnivores /Tertiary Consumers : The animals that eat both
plants and animals. Ex.- man, cat, dog, etc.
d. Parasites : The organisms that live in or on the body of a living host.
Ex.-lice, round worm, leech, tape worm etc.
(iii) Decomposers:The microorganisms that breakdown the complex dead
organic matter into simple inorganic substances and return to the soil so that the
plants can easily absorb. Ex. Bacteria, fungi etc. They are the cleansing agents of
the nature.
B. ABIOTIC COMPONENTS
(i) Air
(ii) Water
Inorganic Nutrients.
(iii) Sunlight
(iv) Temperature
(v) Soil
(vi)
ECOSYSTEM STRUCTURE
The two important structural features of an ecosystem are :
1. SPECIES COMPOSITION :The number of taxonomic species in a given
area and how well each of those species is represented in that area by the number
of individuals in its population . species composition is generally expressed as
percent , so that all species components add up to 100% . This composition can
be calculated with measures of cover , density , weight or biomass .
2. STRATIFICATION :Stratification is the vertical layering of a habitat ; the
arrangement of vegetation in layers. It classifies the layers of vegetation largely
according to the different heights to which their plants grow.Example : In a forest
ecosystem , trees occupy top vertical strata or layer , shrubs the second , herbs
and grasses occupy the bottom layers.
ECOSYSTEM FUNCTION
The major functions of any ecosystem are :
1. Productivity
2. Decomposition
3. Energy Flow
4. Nutrient Cycling
1. PRODUCTIVITY : The rate of formation of biomass per unit area , over a
time period by plants during photosynthesis is called productivity.
 It is expressed in kcal m-2 yr-1( kilocalories per square metre per year) or g
m-2 y-1 (grams per square metre per year).
 Productivity can be of two types :a. Primary Productivity : The amount of biomass or organic matter
produced per unit area over a time period in plants during photosynthesis
is called primary productivity.
b. Secondary Productivity : The production of organic matter by the
consumers is called secondary productivity.
Primary productivity has two aspects :
1. Gross Primary Productivity (GPP) :
 It is the rate of production of organic matter during photosynthesis
in an ecosystem.
 Some GPP is utilized by plants for respiration and some is passed to
the next trophic level.
 Coral reef Ecosystem has the highest GPP.
2. Net Primary Productivity (NPP) :
 It is the weight of the organic matter stored by the producers in a
unit area / volume per unit time.
 It is given by NPP= GPP-R , where R=Respiration losses.
 NPP is utilized by heterotrophs.
 Swamps , marshes and tropical rainforests has the highest NPP .
While deserts have the lowest NPP.
FACTORS AFFECTING PRIMARY PRODUCTIVITY
1. The various plant species found in a particular area.
2. Availability of nutrients ensures greater primary productivity.
3. More the photosynthetic efficiency of the plants (i.e., more efficiency to trap
sunlight) ,more is the primary productivity.
4. Environmental factors ---a. Sunlight : A region receiving maximum sunlight shows more primary
productivity. Example – Tropical region .
b. Temperature : An ecosystem with optimum temperature supports efficient
enzyme activity and hence more primary productivity.
c. Moisture : More availability of water (moisture)/rain , more is the primary
productivity. Example – Deserts have lowest primary productivity due to scarcity
of water.
2.DECOMPOSITION :The process of breaking down complex organic matter
into inorganic substances like CO2, water and nutrients is called decomposition .
The raw materials for decomposition like dead plants , animal remains and their
faecal matter are called detritus.
STEPS IN DECOMPOSITION :
A. Fragmentation : The process of breaking down of detritus into smaller
particles is called fragmentation . Example : Earthworms breakdown the detritus
into small pieces.
B. Catabolism : The enzymatic process by which degraded detritus is converted
into simpler inorganic substances is called catabolism.
C. Leaching : The process by which water-insoluble inorganic nutrients go down
into the soil horizon and get precipitated as unavailable salts is called leaching.
D. Humification : The process of accumulation of a dark coloured amorphous
substance called humus and undergoes decomposition at an extremely slow rate
is called humification.
E. Mineralisation : The process by which humus is further degraded by some
microbes to release inorganic nutrients is called mineralization.
FACTORS AFFECTING DECOMPOSITION
(1) Chemical Composition of detritus :
 If the detritus is rich in lignin and chitin , the decomposition rate goes
slower.
 If the detritus is rich in nitrogen and water-soluble substances like sugars ,
the decomposition rate becomes faster.
(2) Climatic factors :
 Warm and moist environment favours decomposition of organic matter.
 Low temperature and anaerobic conditions inhibit the rate of
decomposition.
3. ENERGY FLOW :The food (energy ) flows from one organism to another in
an ecosystem through food chains .
The flow of energy in any food chain is always unidirectional because the energy
once passes from one trophic level to another trophic level in a food chain is not
reverted.
 The sun is the only source of energy for all ecosystems on earth.
 Out of the total incident solar radiation , only 50% of it is
photosynthetically active radiation (PAR).
 Green plants ( producers) capture 2-10 % of the PAR and convert it into
food energy(chemical energy).
 When green plants are eaten by primary consumers/ herbivores ,only 10%
of the energy passes on to the secondary consumers/carnivores ,while
maximum energy is lost as heat during metabolic activities like respiration.
 Further 10% of energy passes from the secondary consumers/carnivores
to the tertiary consumers/ top carnivores .
 There is maximum energy available at the first level(producer level) and
further goes on decreasing from second, third and to the fourth level. The
fourth level receives the least energy.
 Lindeman’s (1942) 10 % law states that at each step of food chain , when
food energy is transferred from one trophic level to the next trophic level,
only about 10 % of energy is passed on to the next trophic level.
ENERGY FLOW IN AN ECOSYSTEM:
R = Respiration
FOOD CHAIN
It is the transfer of food (energy) from one organism to the other.
OR
It is the sequence of organisms through which the food(energy) is transferred
from producers to the consumers.
Examples :(i) Terrestrial food chain (like grassland or forest):
Grass----->Grasshopper ----->Frog ----->Snake----->Eagle.
Grass -----> Deer ----->Lion .
(ii) Aquatic food chain (like pond) :
Phytoplankton------>Zooplankaton ----->Fish------->Crane.
Significance :
(i) Transfer of food (energy).
(ii) Study the food relationships and interactions among various organisms in the
ecosystem.
(iii) Maintains ecological balance.
Disadvantage :
Harmful toxic chemicals are transferred from one organism to another organism(
throughBiomagnification).
FOOD WEB
It is the network of various interconnected food chains.
Snake
Vulture
Frog
Grass hopper
Lion
Cow
Grass/Plants
Deer
DIFFERENCES BETWEEN FOOD CHAIN AND FOOD WEB:
FOOD CHAIN
FOOD WEB
1. It is the sequence of organisms
through which the food (energy) is
transferred from producers to the
consumers.
1. It is the network of various
interconnected food chains forming a
web-like pattern.
2. One organism holds only one
position.
2. One organism can hold more than
one position.
3. The flow of energy can be easily
calculated.
3. The flow of energy can not be easily
calculated easily.
4. It is always straight.
4. It is like a network.
TYPES OF FOOD CHAINS :
There are two types of food chains :
1. Grazing Food Chain (GFC) :The type of food chain in which the flow of
energy is from the autotrophic plants to the herbivores and then to carnivores.
Example : Grass -------> Rabbit ---------> Lion.
2. Detritus Food Chain ( DFC) : The type of food chain in which the flow of
energy is from the dead organic matter to the microbes ( like bacteria and Fungi )
and then to detrivores like earthworms.
Example : Dead leaves ----------> Fungi---------> Earthworms/ Centipedes/
Millipedes.
GRAZING FOOD CHAIN (GFC)
DETRITUS FOOD CHAIN (DFC)
1. It starts with the green plants
(producers).
1. It starts with the dead organic matter
or detritus.
2. Less fraction /amount of energy
flows through this type of food chain.
2. More fraction /amount of energy
flows through this type of food chain.
3. Energy for food chain comes from
sun.
3. Energy for food chain comes from
organic matter (detritus).
TROPHIC LEVELS
The various levels or steps in a food chain.
OR
The place or position occupied by an organism in the food chain is known as
trophic level.
T1= First trophic level is occupied by the plants ( producers).
T2= Second trophic level is occupied by the Insects ( primary consumer).
T3= Third trophic level is occupied by the Frogs ( secondary consumer).
T4= Fourth trophic level is occupied by the Hawk ( tertiary consumer).
ECOLOGICAL PYRAMIDS
Each trophic level of the ecosystem can be represented by graphical designs
called ecological pyramids. It shows producers at the bottom followed by various
trophic levels like herbivores , carnivores etc.
OR
The relation between producers and consumers in an ecosystem can be
graphically represented in the form of a pyramid called ecological pyramid .
Ecological pyramids are of three types :
1. Pyramid of Biomass : This shows the amount of biomass in trophic levels. It
is inverted in an aquatic ecosystem.
2. Pyramid of Number : This shows the number of organisms in each trophic
level in a food chain. The number of pyramid is inverted in a tree ecosystem.
3. Pyramid of Energy : This shows the flow of energy through the food chain.It
is always upright.
DISADVANTAGES OR LIMITATIONS OF ECOLOGICAL PYRAMIDS :
1. It gives idea of a simple food chain , which never actually exists in nature.
2. Decomposers/ Saprophytes are not given any position in the food chain inspite
of their significant role.
3. It never considers the same species belonging to two or more trophic levels.
4. NUTRIENT CYCLING : The movement of nutrient elements through
various biotic and abiotic components of an ecosystem is called nutrient cycling
.The total amount of nutrients like carbon , phosphorous , calcium etc. present in
soil at any time is called standing state.Hence, nutrient cycling is another
function of the ecosystem.
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