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LESSION-2

ECOSYSTEM: STRUCTURE OF ECOSYSTEM

Dr. Nibedita Khuntia
Assistant Professor,
Maharaja Agrasen College,
University of Delhi.

INTRODUCTION
We are not alone in this world. We share our resources with other life forms. There are non-
living things around us as well. Throughout our lifetime we keep on interacting with other
living beings and non-living things.

LEARNING OBJECTIVES
After going through this lesson, you will be able to
1. Know the concept, definition and structure of ecosystem.
2. Distinguish between biotic and abiotic components of ecosystem.
3. Explain the different types of ecological pyramids.
4. Understand the term ecological succession.

1. CONCEPT OF ECOSYSTEM
Ecosystem is the basic structural and functional unit of the environment. Both the living and
non-living component of the nature, when interact with each other to establish a stable living
community, it is called as Ecosystem. That means there is a constant exchange of something
between these living & non-livings, is called an Ecosystem. Without the living component,
establishment of an ecosystem is not possible and vice versa. Both are two sides of a coin or
very much complementary to each other.
The study of ecosystem includes complete analysis of the structure, regulation and the role of
each and every component functioning there. Once we know it, in detail, the study of the
ecosystem and its importance to the equilibrium of environment will be understood easily.

2. DEFINITION OF ECOSYSTEM
The study of all the physical as well as biological processes including the distribution and
abundance of living organisms and the interaction in between them with their surrounding
environment is known as Ecosystem. In simpler words, if any environmental changes occur
in the physical or abiotic factors, they in turn change the type and number of the organisms
that is both the plants and the animals, present in that particular area.

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The ecosystem is very complex in nature and human beings are a part of the ecosystems also.

The theme of the ecosystem is “energy flow”. Sustenance of ecosystem is possible due to the
energy dependence as well as energy transfer between various components of an ecosystem
may it be living or non-living.

Examples of Ecosystems: Terrestrial or land-based ecosystem, Aquatic or water-based

ecosystems etc.

3. STRUCTURE OF ECOSYSTEM
It is very easy to study or understand the structure of ecosystem from the flow chart described
(Fig.1) below.

ECOSYSTEM

BIOTIC COMPONENTS ABIOTIC COMPONENTS

LIGHT
PRODUCERS
CLIMATIC FACTORS
TEMPERATURE

CONSUMERS
WATER

DECOMPOSERS EDAPHIC FACTOR SOIL

Fig.1.Schematic Representation of Structure of an Ecosystem

3.1. BIOTIC COMPONENTS

Biotic components are also divided into 3 categories basing upon their food-fed relationships
(Fig.2).
3.1.1. PRODUCERS: Producers are the autotrophs (auto means self, troph means to
nourish) of the ecosystem. They are the green plants and green microorganisms who
can make their own food material by using carbon dioxide and water in presence of
sunlight with the help of chlorophyll present in them.
Ex. All green plants, Algae, Cyanobacteria,

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3.1.2. CONSUMERS: Consumers are the heterotrophs (hetero-not self troph to nourish) of
an ecosystem. They depend on the producers of the nature to get energy. Consumers
are also different types like
a) Primary Consumers – They are the herbivores who eat directly the autotrophs /
plants. They cannot eat any animals.
Ex. Grasshoppers, Rabbits, Goats.
b) Secondary Consumers – They cannot directly eat the producers of the
ecosystem, that is the plants. They can eat only herbivores.
Ex. Frogs, Jackal, Snakes
c) Tertiary Consumers – They are carnivores in nature means they are the meat
eaters. Thus, they depend on the secondary consumer for their food. They are the
top-level carnivores.
Ex. – Tigers, Lions, Vulture, Kite
3.1.3. DECOMPOSERS: Decomposers are also to some extent heterotrophic in nature.
They do not contain chlorophyll, so depend on other material for food and energy.
These organisms can grow on the dead and decay materials of the environment. That
is why they are known as the decomposers or saprophyte, or scavengers of the nature
or they can be called as the detrivores (Detri means dead particulate organic material).
They can live in any type of soil with organic waste. They play a very important role
for the completion of the Biogeochemical Cycle in the environment.
Ex. Bacteria, Fungi, Earthworm

Sr.No. Type of Primary Consumer Secondary Tertiary Consumer

Consumer
Ecosystem

1 Grassland Grasshoppers, Rabbits, Frogs, Lizards, Hawks, Eagle, Tiger

Ecosystem Deer, Sheep, Goats etc Birds, Snakes Etc
2 Forest Leafhoppers, Bugs, Flies, Birds, Owl, Tiger, Lion etc
Ecosystem Squirrels, Insects, Deer, Lizards, Wolves,
Fruit bats, Nilgai, Jackals, etc.
Elephants etc.
3 Desert Insects, Rats Birds Camel, Scorpions, Fox, Snakes, Fox, Striped
Ecosystem Squirrel Jackal, Rattle Hyena, Sand Cats, Viper,
Snakes, Mongoose Saharan Cheetah, Eagles,
etc Kites etc.

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4 Pond or Insects, Frogs, Larvae, Insects, Larger Largest Fishes, Water

Lake Beetles, Zooplanktons, fishes, Cranes, Snakes, Hawks etc.
Ecosystem Crustaceans etc Other Birds

5 Marine Zooplanktons, Crustaceans, Bigger Fishes, Giant Carnivorous Fish,

Ecosystem Small fishes Mackerel etc Sharks,
Whales, Snakes,
Hawks etc

Table-1: Different living organisms or biotic factors in consumer forms in different

Ecosystems

Fig.2. Relation between Producers, Consumers and Decomposers

Ref: https://archive.bigelow.org/bacteria

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3.2. ABIOTIC COMPONENTS:

These are the non-living factors in form of solid, liquid or gas found in the nature (ice, water,
moisture). They can be categorised into 2 types.
I) Climatic factors
Ex. Light, Temperature, Humidity, Rain etc.
II) Edaphic factors
Ex. Soil, Organic and Inorganic components of the soil, Substratum etc.
Let’s discuss importance of each abiotic factors and their limitations in an ecosystem.

3.2.1. CLIMATIC FACTORS

3.2.1.1. Light – It is an essential factor for all the living organisms like producers, consumers
as well as decomposers. In presence of the sunlight plants are able to prepare their
food material, which in turn eaten by the heterotrophs & ultimately by the
decomposers. Without sun light photosynthesis is not possible thus it is one of the
most important abiotic factors of an ecosystem. Quantity as well as quality of light
has different impact on different organism. Let’s discuss.
i) Importance of light for plants
a) Chlorophyll production
b) Distribution of plants: The vegetation or the types of plants grow on the
earth depends on the amount of sunlight they are getting. Thus the
vegetation of temperate, tropical as well as Tundra regions are different from
each other.
c) Light thus decides the physiology of the plants of different regions.
d) Temperature: When light increases, temperature also increase and vice
versa. When temperature increases rate of transpiration in the plants
increases. Thus, the absorption of water from the underground also
increases. It clearly explains that temp also plays an important role and
decides the type of plants to grow in a particular area.
e) Stomatal Movement: The stomata are present in the leaves of the plants.
They control the evaporation of water from a plant body. Thus, by opening
and closing, stomata keeps the plant body in a stable physiological status.
f) Duration of Light: During summer and winter months the type of flowers,
what we can observe in the nature are different. The basic theory behind it is
some plants can bloom in summer months are long day (basing on the
exposure to the sun light) plants and some are short day plants (less exposure
to sunlight or natural light).

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ii) Importance of Light for animals

a) Metabolism: Light controls the physiology & metabolism of animals by
affecting it’s enzymatic activity.
b) Vision: Without light it is very difficult to see anything. So it is required by
all animals.
c) Pigmentation: The process of pigmentation on the skin color depends on the
natural light source.
d) Reproduction: Different animals respond to different duration of light
exposure for their breeding activities.
e) Circadian Rhythm: Daily response of the animals towards the light condition
are known as circadian rhythm. This is an important physiological action of
all the living organisms. Thus, it is a light dependent process.
3.2.1.2 Temperature: Temperature affects animals and plants in following ways.
i) Importance of temperature for plants
a) Metabolism: Temperature increase the physiological activity. Thus, the
types of plants grow in a desert ecosystem are different from the type of
plants of a forest ecosystem and an aquatic ecosystem.
b) On Growth & Development: Different types of plants need different range of
temperatures for their growth. Summer growing plants are different from
winter season growing plants. This is self-explanatory.
c) Thermal Stratification: Best example is an aquatic ecosystem. The organism
growing at surface layer are different as they need more temperature and
light than the organisms grow at a deeper level in an aquatic ecosystem.
ii) Importance of Temperature for Animals
Basing on need of the temperature, animals are categorised into two types. Like:
a) Warm-Blooded or Endo- thermic animals
b) Cold – Blooded or Ecto-thermic Animals
Warm blooded animals maintain their body temperature at a constant level. Their body
temperature does not change with the environment temperature.
Ex. Mammals, Birds, etc.
The body temperature of the organism when changes with the temperature of the
environment, then they are known as Cold Blooded animals.
Ex. Frogs
c) Migration: Temperature is also a factor for migration of animals. It is
known as thermal migration. If temperature changes the locomotory animals
or birds may change their places for a temporary period & them comeback to
their original ecosystem when the weather changes.

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3.2.1.3. Water: Life is never possible without water. So, water is a very important abiotic
factor in an ecosystem. The amount of water present in an area decides the type of
ecosystem to be developed there. In this regard sometimes aquatic ecosystems also
develop for ex. Pond & Lake ecosystems. If for a longer period of time, due to any
reason, a huge amount of water got deposited & replenished repeatedly due to rainfall
etc., then through the process of succession an aquatic ecosystem develops and get
established there.
Beside for photosynthesis & other metabolic activity plants needs water for
circulation of minerals throughout its body.
Water is also an essential requirement of the animals for their metabolic activity.
Water regulates the body temperature of both plants and animals.
Water in forms of rainfall also needed by the ecosystem. It maintains the humidity &
content of moisture in the atmosphere. Amount of rainfall also decides the kind of
plants to grow over there.
Ex. Deciduous forest, Evergreen forest, Deserts etc.
With the type of vegetation, different types of animals also started living in that
particular geographic area.
Water in form of humidity also affects plants and animal lives. Some plants can grow
in less humid area where some other plants need more moisture in their environment.
Some plants can use atmospheric moisture directly from the environment.
Ex. Epiphytes, Orchids, Lichens, Mosses etc.
Some other needs it in liquid form from underground by the process of absorption.
Ex. Higher plants.

3.2.2. EDAPHIC FACTORS

3.2.2.1. Soil: Soil is a natural resource and provides platform for the plants to grow &
animals to dwell on it. Thus, the fertility and quantity of soil decides the type of
vegetation in that area. To be more specific, pH of the soil is the deciding factor. If pH
of the soil is less than 7, then it is acidic soil & if pH is more than 7 it is alkaline.

Fig.3: Schematic representation of different texture of the soil

(Ref:https://upload.wikimedia.org/wikipedia/commons/4/45/Horizons.gif)

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Thus, the acidity

T a & alkalinity
a off the soil decides
d the number & kind of plantsp &
animals to stay over thhere (Fig.3)). But needless to say, neutral soiil, i.e. when
n the pH
ranges from
m 6.5 -7.5 iss the preferrred conditio
on for most of the livingg organism..
Soil is also associated with different kinds off minerals & nutrients.. Some are required
r
in more quuantity, are called maccronutrient and some are micronnutrients wh hich are
required inn a small quantity. TheyT also play a vittal role in developm ment and
sustenance of an ecosyystem.
Texture of the soil is also playinng a key ro
ole. For ex. Rocky areeas, Swamp
py areas,
Mining areas etc.
Different teextured soil will allow different ty
ypes of biotiic factors orr organisms to grow
and establissh in that eccosystem.

4. ECO
OLOGICAL
L PYRAMIIDS
By noww we are cleear that the ecosystem can sustain ns itself, if there
t is a bbalance betw
ween the
produceers, the connsumer andd the decom mposers. En nergy is a major
m link wwhich bindss all the
above components
c s in an ecosyystem. Thuss, there is a fixed positiion or level of a particu
ular type
of orgaanisms in ann ecosystem m. How we can know or decide that t positioon? To expllain it, a
graphiccal structuree has been proposed
p byy the enviro onmental bioologists, knnown as pyrramid or
Ecologiical Pyramid (Fig.4).

Fig.4: Schem
matic repressentation of an Ecologgical Pyram
mid
mids)
(Ref:htttps://sites.google.com/sitte/vhs2015ennvironmentallscience/bioddiversity/ecological-pyram

Definitiion: An ecoological pyrramid is a graphical

g reepresentatioon of the reelationship between
b
various trophic levvels organism
ms in a Foood Chain.
It was first
f designeed by Charlees Elton andd are called Eltonian Pyyramid or F
Food Pyram
mids.
Ecologiical Pyramids are threee types:
1. Pyrramid of Nuumber

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2. Pyramid of Biomass
3. Pyramid of Energy
A. Pyramid of Numbers:
As the name says, in this type of pyramid number of organisms are counted and accordingly
respective volume to each trophic level is allotted in the pyramid. Characteristic features of
pyramid of number are.
1) Number of producers are higher in number than the consumers present in other trophic
levels.
2) Number of individuals in each trophic level decrease when we go from bottom to top
in a pyramid.
3) Collectively the living organisms present in each of the trophic levels are known as
standing crop.
4) Normally the pyramid of number is an upright (Fig.5) one Ex. Grassland ecosystem,
Aquatic ecosystem.
5) Sometimes inverted pyramids (Fig.6) are also found in this case.
6) A mixed or spindle shaped pyramid is also observed in case of forest ecosystem.

Fig.5: Upright Pyramid of Numbers

(Ref: https://www.pmfias.com/ecological-pyramids-pyramid-numbers-biomass-energy/)

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Fig.6: Inverted and Spindle Shaped Pyramid of Numbers

(Ref: https://www.pmfias.com/ecological-pyramids-pyramid-numbers-biomass-energy/)

B. Pyramid of Biomass: Biomass is the total dry weight of the animals as well as plants
present in the ecosystem at any point of time.
Like pyramid of numbers it may be upright one or inverted one. In case of a forest
and grass land ecosystem it is upright and in cases of a pond ecosystem inverted
pyramids (Fig.7) are observed.

Fig.7: Upright and Inverted Pyramid of Biomass

Ref:https://www.tutorialspoint.com/environmental_studies/environmental_
studies_ecological_pyramid.htm

The figures show the position of different organisms in different trophic levels.

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C. Pyramid of Energy
As already mentioned, the Food Chain and Food Web systems are existed for the energy
requirement and energy transfer between the living organisms in an ecosystem. It is the
most important type of ecological pyramid. The amount of energy being transferred from
the lower trophic level towards the upper ones become less and less. Thus, longer the
pyramid in height, lesser will be the amount of energy to reach the organisms present in
the topmost trophic level. Only 10% of the energy is being transferred to the subsequent
upper trophic level organisms (Fig.9). For example, if the producers generate 1000 kilo
calorie amount of energy, the primary consumers will receive 100 kcal, the secondary
consumer will get 10 kcal and only 1 kcal amount of energy will reach to the tertiary or
topmost level of consumers.
In this way a pattern of upright Pyramid of Energy (Fig.8) will be developed for all types
of ecosystems found in the Nature. This is the universal formula. Energy pyramid can
never be an inverted one or spindle shaped found in other types of ecological pyramid
structure. The shape of the pyramid of energy is not affected by the size, biomass, number
or the metabolic rate of the organisms.

Fig.8: Structure of Pyramid of Energy

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Fig.9: Energy Flow 10% rule in an Ecosystem.

(Ref:https://www.tutorialspoint.com/environmental_studies/environmental_studies_ecological_pyramid.htm)

Some limitations are also observed in the studies of ecological pyramids. That can be
described as follows:
1. The position of certain organisms are not fixed in one ecological pyramid. That may vary
in same or may be in a different ecosystem.
2. There is no consideration of seasonal changes, while studying the pyramids
3. Role of detrivores are not represented in an ecological pyramid.
At last it can be said that the pyramid of energy is very accurate and gives a true picture of
the ecosystem.

5. ECOLOGICAL SUCCESSION
Ecological succession term was coined by Hult (1885). Famous ecologist Clement defined
Ecological Succession as “the natural process by which the same locality becomes
successively colonised by different groups or communities of plants”.
Characteristics of Ecological Succession:
1) The species types and the community changes in an orderly process
2) The physical structure of a community changes by the biological action of the biological
factors grow there.

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3) At last a stable ecosystem m gets estabblished in an

n area. Withh both biotiic as well ass abiotic
facctors interaccting there to establish equilibrium
m in that ecoosystem.
4) Thhen the cliimax commmunity getts establish
hed there, which in turn main
ntain an
equuilibrium with
w the enviironment.

Scheematic Reprresentation of a Forest Successionn

(https:///upload.wikkimedia.org//wikipedia/commons/4
4/41/Forest__successionn_depicted_o
over_ti
me.png:)

Causess of Ecologiical Successsion

a) Initial causess: It happens for the destruction off an existingg habitat. It is two types.
i)) Climatiic Factors:
E Soil Eroosion, Soil deposition
Ex. d d to heavy
due y wind, Conntinuous floood, Heavy rainfall,
Fire, Drrought, Lannd Slides, Oil Depositio
on etc.
iii) Biotic Factors:
F
Ex. Defforestation, Over grazinng, Jhum cu
ultivation ettc.
b) Coontinuous Causes:
C It is
i responsibble for the changes
c in population
p ccompositionn in that
areea. The facctors responnsible for population
p compositioons are, miigration forr safety,
miigration duee to urbanizzation, miggration due to industrialization, m
migration foor better
life
fe etc.

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c) Stabilizing Causes: Stabilization of an ecosystem happens due to the climatic condition

of that area, availability of minerals, fertility of the land for agriculture as well as growth
of different types of producer for a continuous flow of food and energy as discussed
earlier.
Types of Ecological Succession
1) Primary succession: It begins from the primitive substation where there was no living
factor before.
Ex. Volcanic eruptions, Rocky Areas etc.
2) Secondary Succession: It begins from a previously sustained living matters, but the
vegetation got damaged due to any climate factors like flood, fire, acid rain etc.
3) Autogenic Succession: (Auto means self or same, and genic means producing / causing)
The developing plant community brings a change in the condition of a particular place,
which is not suitable for them, but creates or produces an environment for the growth of
a different community. It is a succession driven by biotic components of an ecosystem.
4) Allogenic Succession: (It is caused by abiotic factors) In contrast to autogenic
succession, allogenic succession is an abiotic factor driven condition. The habitat of the
ecosystem is changed due to volcanic eruption, climate change, comet strike, earthquake,
flood, drought etc.
5) Induced Succession: It is a man-made process, developed for the benefit of the
humankind.
Ex. Cultivation of Crops in a field.
6) Autotrophic Succession: When a place is rich in inorganic content & poor in organic
matter, the development of succession of plants over that area is called as autotrophic
succession.
7) Heterotrophic Succession: If a succession begins in an area which is rich in organic
contents like forest litter, sewage etc, and dominated by saprophytes like fungi,
mushrooms etc is called heterotrophic succession.
8) Retrogressive Succession: Sometimes due to heavy biological or biotic interferences, the
succession goes backward instead of progressing. Ex. Forest community changes to a
shrub land or grassland or to a barren land due to deforestation and overgrazing.

LEARNING OUTCOME
Ecosystem is the study of living organisms with its surroundings. Thus, it’s an
interdependence of biotic and abiotic factors in an area. Presence of only one factor cannot
create an ecosystem. In an ecosystem position of different organisms are different. This has
been explained through ecological pyramids. The principle of ecological pyramid depends on
the food habit of the organisms present in that ecosystem. The development of a new

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ecosystem on a barren land is known as succession. Sometimes reverse succession also

happen that is a well-functioning ecosystem may get destroyed due to some artificial i.e.
manmade or due to some natural calamities and gets converted into a barren land.
Some Important Terms used in the Lesson

Allogenic Succession Ecological Pyramid

Autogenic Succession Ecological Succession
Autotrophs Ecosystem
Autotrophic Succession Edaphic Factors
Abiotic Components Heterotrophic Succession
Biotic Components Heterotrophs
Biomass Induced Succession
Climatic Factors Primary Succession
Decomposers Retrogressive Succession
Detrivores Secondary Succession

PRACTICE QUESTIONS

I. Multiple Choice Questions:

1. Which one of the following is a biotic factor in an ecosystem.
a) Oxygen, b) Soil, c) Rocks, d) Lizard
2. ---------------- is an autotroph.
a) Fungi, b) Tiger, c) Rabbit, d) Algae
3. Which one of the following is decomposer in an ecosystem.
a) Squirrel, b) Insects, c) Earthworms, d) Lizard
Ans-1(d), 2(d), 3(c)
II. Write Short Notes on:
1. Consumers
2. Pyramid of Energy
3. Water as an abiotic factor
III. Long Questions:
1. What do you mean by an Ecosystem.
2. What are the ecological pyramids in an ecosystem.
3. What is succession in an ecosystem. Explain in detail what you know about it.

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