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Ecosystem

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Study of our ecosystem for dummies.

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Unit-2 Ecosystem
§2.1 Concept of Ecosystem (= Biotic + Abiotic)
• An ecosystem is a biotic
assemblage of plants, animals,
microbes and its interactions.
• Eco = environment, System = coordinated units.
• Ecology→study of ecosystems
• The first law of ecology is that everything is related to
everything else -Barry Commoner.
• Ecology deals with the study of organisms with the surrounding.

§2.2 Ecosystem Structure
§2.2.1 Biotic Structure (plants, animals & microorganism)
• In an ecosystem the biological cycling of materials is
maintained by three groups viz. producers, consumers and
decomposers/recyclers.

Plants

• •

• • ••• • • •
• •• • •• ••
• •

Animals
Producers

Consumer
s

Microorganism
Recycler
s

Animal can’t synthesis food depend on plant→Plant can’t synthesis food depend
Abiotic→ Sun, carbon dioxide, minerals etc in the environment.

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• Nature is capable of sustaining the producer-consumerdecomposer cycle indefinitely.
• Producers: Green plants→ synthesize their food by
photosynthesis (Chlorophyll+CO2).
• Consumers: 1. Herbivores: (Plant eaters) eg. Rabbit, man,
insects.
2. Carnivors: (meat eaters) eg. Dependence on
the consumers
(secondary consumers).
3. Omniovers: (plant and meat eaters) Human,
fox, many birds
4. Detritivores: (dead organism eaters) ants,
crabs, earthworms.
• Decomposers:
Various bacteria and
fungi→ decompose the
complex organic
molecules
• In some conditions,
producers dominates
(forest), consumer
predominates (ocean)

§2.2.2 Abiotic Structure
(plants, animals &
microorganism):
• Climatic factors,
geographical factors,
energy, toxic
substances etc.
• Physcial factors:
Sunlight, temperature,

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soil type, water availability etc influence the ecosystem. (eg.
Desert and rain forest)
• Chemical factors: Carbon, nitrogen, phosphorus, potassium,
oxygen, sulphur and toxic substances

§2.3. Function of ecosystem:
• Ecosystem perform under natural conditions continuously
• Energy receive from Sun (water+nutrients+air) and pass
through various biotic components → so life is the flow of
energy
• Following are the major functionalities
a.
b.
c.
d.
e.

Food chain & food webs
Energy & Nutrient flow
Cycling of nutrients (biogeochemical cycles)
Primary and secondary production
Ecosystem development & regulation

§2.3.a Food chain & Food Webs:
• Food Chain:
o It is a path way/cycle of food from and back to producer
o or sequence of eating and being eaten in ecosystem.
o Eg.1: grass→grasshopper→mouse→snake→hawk
(Grassland ecosystem)
o Eg.2: Phytoplantons (algaes) →water fleas→small
fish→Tuna (carnivorous fish)
(Pond ecosystem)
o Eg.3: Dead Organic matter→fungi→bacteria
(Forest ecosystem)
• Food web:
o Combination/interconnection of different Food Chains
o There are number of options of eating and being eaten at
different levels.
Food Chain→Food Web→Trophic structure (Ecosystem)

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Snake

Hwak

Rabbit
Toad (pre frog)
Spider
Grasshopper
Grass

Preying Mantis (carnivore)

Sparrow
Mouse

Example-1: (Food-Chain)

Example-2: (Food Web, Many food chains)

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§2.3.b Energy & Nutrient Flow:
Sun

Heat

Producer

Heat
Consume
r

(Decomposer=Recycler)
Nutrient

Decomposer
Heat

Energy and Nutrient too move through the food chain & ultimately
reached to dead organic matter (decomposition by micro-organisms)

• Plant system having highest form of energy and decreases with
increase in the path of the food-chain.
• Energy can flow in one direction only.
• Ecological Pyramids: Graphical representation of structure
and an ecosystem, starting with producer at the bottom and
each successive level forming the apex is know as ecological

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pyramid. (See the picture: Trend is same for energy system
also (producer to recycler))
• Energy laws:
Ist law: Energy can neither be created nor be destroyed,
but it can be transformed from one form to another.
2nd law: Energy transformation involves degradation or
dissipation (distribution) of energy from a concentrated
form (not directly transformed). (Roughly ~10% of energy
is transformed to one to another system, rest are heat
energy only).
• Sun as the prim source of energy:
To do photosynthesis and oxidation reduction reactions
occurs in plants etc.

§2.3.c Nutrient Cycling:
• Carbon, nitrogen, sulphur, oxygen, hydrogen, phosphorus etc
move in circular paths through biotic and abiotic components →
biogeochemical cycles.

• Water cycle→ hydrological cycle
• Carbon cycle:
o Carbon dioxide is the prim
source for the carbon.\
o It is a gaseous cycle.
o All organic compounds contain
large amount of carbon source
(carbohydrate, protein, amino
acid).

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o Main steps:
o Green plant: Photosynthesis (CO2+light →
Carbohydrate+O2)
o Plants were eaten by Human and Animals (carbohydrate
transfer)
o Risperation of Biotic systems (O2→ CO2) liberates CO2
o Combustion of organic matters, dead plants, animals &
Coal release CO2
o Volcanic eruptions also release large CO2
o The cycle goes continuous with loss.

• Oxygen (O2) Cycle:
o Oxygen is vital for life in the biosphere
o Photosynthesis is the prim source of
systems for the O2 production from the
Carbon dioxide (CO2).

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• Nitrogen (N2) Cycle:
o 78% of nitrogen gas present in the atmosphere.
o Nitrogen is taken by plant and used in metabolism for
biosynthesis of amino acids, proteins, vitamins etc.
o After death of plants and animals→ ammonifying &
nitrifying bacterias convert them in to ammonia (NH3),
nitrite (NO2-) and nitrate (NO3-), which again used by
plants.

Amino acid,
proteins, vitamins
etc

• Phosphorus Cycle
o Phosphorus is an essential nutrient for plants and animals
in the form of ions PO43- and HPO42-.
o Source of phosphorus lies in the rocks, fossils (dead
animal and plant have hardened into rock)

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o Formers use the phosphate→run off→ river→ocean/settle
in deep sediments (difficult to regenerates)
o Sea fish→Sea bird→ land

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§2.3.d(i) Primary Production:
• Rate at which radiant energy is converted into organic
substances (eg. Carbohydrate) by photosynthesis or chemicalsynthesis by primary producers. (Net power of chemical energy
production)
• Net primary production (NPP) = Overall production (or Gross
Primary production, GPP) –
Respiratory loss (R).
NPP = GPP-R
GPP = CO2 + light+(Photosynthesis) → Carbohydrate (100%) + O2
R = Carbohydrate (x) + O2 → energy + CO2
NPP = 100 - x
• NPP depends on

Ecosystem
Deserts based
Open Oceans
Grasslands
Moist Temperature Forests
Agro-ecosystems
Wet tropical forest

(1) Solar radiations
(2) Availability of Water
(3) Nutrients
(4) Nature and type of Plant with
chlorophyll content.

Gross Primary Production (GPP)
K Cal/m2/yr
200
1000
2500
8000
12000
20000

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§2.3.d(ii) Secondary Production
• Net Energy production (in the forms of chemicals, eg.
Carbohydrate) in Herbivores or carnivores by using primary
producer (plant) (after respiratory loss).

§2.3.e Ecosystem Regulation
• Ecosystems regulate themselves and maintain themselves
under set of environmental condition (Reversible) [or regulates
its internal environment so as to maintain a stable]
• Ecosytems tries to resist the change and maintain equilibrium
with the environment due to the property known as
Homesostasis.
+ve
Feedback

System
Function

-ve
Feedback
-ve
Feedback

Death or
Collapse

Hemeostatic
plateau

+ve
Feedback
Death or
Collapse
(-)

(+)
Stress condition

• The shows tolerance within certain extent→ some counteract
(deviation) know as with negative feed back (mechanism) →
bring back to original stage.
• To intense stress leads to positive feed back (mechanism,
irreversible) mechanism → tends to away from optimal
condition → death or collapse

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§2.4. Ecological Succession
• Changes in an ecological system due to the external change.
• The progressive replacement of one community (group of
plants & animals living in an area) by another till the
development of stable community in that particular area
• Stages of Ecological Succession:
o (a) Pioneer community: First group of micro-organism,
which establish their community in the area.
o (b) Seres (or) Seral Stage: Various development stages
of a community.
• Type of Ecological Succession: (Environmental basis such a
terrestrial (living land), fresh water or marine etc)
o Primary Succession: (Drastic change): Eg. at Island,
sand, silt bed (river opening), new volcanic flow etc.
When community begins to develop
on a site previously unoccupied
by living organisms.
(see below)

o The sere development involved with the process called
presere.

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o Secondary Succession: (normal change/time): When
an existing community is disrupted and a new one
subsequently develops at the site.
Eg. at: Some natural catastrophe (sudden event
that causes very great trouble or destruction) such
as fire or landslide, flooding, deforestation, mining.
(see below stages):

Following picture is an example for primary and secondary
successions stages.

(Horiculture- study about gardening)

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§2.x. Ecological Pyramids: (It is a graphical representation of
structure and function)
Eg.: Food chain process
Producer→ consumer →decomposer (recycler)
There will be regular increase in the properties (energy,
biomass and no. of organisms)
• Type of Ecological Pyramids:
o 1. Pyramid of Numbers
o 2. Pyramid of Energy
o 3. Pyramid of Biomass

§2.x.1. (1) Pyramid of Numbers:
o Representation of individual organism present in each
tropic level. Eg. A grassland Ecosystem.
o
 3rd tropic level: (carnivores) less than the herbivores
o
 2nd tropic level: (herbivores), less compared to the
grass
 1st tropic level: grass small in size larger in number
o (2) Pyramid of Energy: Amount of energy present differ
from different levels.

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o (3) Pyramid of Biomass: Total weight/volume of the dry
matter present in different tropical systems (eg. tree→
hawk).
* Inverted pyramid in an aquatic
system (fish→ plant):
Carnivore: Big fishes 12 gm/m2
Herbivores: 8 gm/m2
Producer: 4 gm/m2

§2.5. Major Ecosystems (some)
§2.5.1. Forest Ecosystem
• Rich is trees interspersed (irregular mixing)with herbs, shrubs
(round shaped flowers), climbers, lichens, algae, variety of
animals and birds etc (rich biodiversity) → in undisturbed and
stable climate condition
Shrubs

Lichens

Algae

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§2.5.1.A Tropical Rain forest:
• Evergreen forest found near the
equator
• Always with high temperature, high
humidity and high rainfall→favor for
fast trees growth
• Different types of layers or plants and
animals in the tropical Rain forest :>
o Emergent Layer: Top most
layer
o Canopy: below the Emergent.
Layer. Bright (umbrella like
tree cover), Birds, insects here
only
o Understory: below canopy,
Receive very low
sunlight→dark leaves(high
chlorophyll) (wood climbers, same kind of orchids which
are attached to branch of trees)
o Floor: Lowest layer. Receives very low sunlight

§2.5.1.B Tropical deciduous forest:
• Not ever green, loses its leaves in autumn
and grows new ones in the spring.
• Little away from the equator (warm
climate round the year, Rain only in the
monsoon), Many timings the climate is
dry only.
§2.5.1.C Tropical scrub forest:
• Where the dry season is longer
• Here small deciduous trees and shrubs only

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§2.5.1.D Temperature Rain forest:
• Found in temperature area with adequate rain in forest.
• Dominated by coniferous trees (evergreen tree which produce
fruit in the form of cones)

§2.5.1.E Temperature deciduous forest:
• Found in moderate temperature
• Seanson: Long summer & cold but not too
severe winter, moderate rain. (contains
large oak trees)
§2.5.1.F Temperature coniferous forest:
• Fond in the arctic area (tundra)
• Winter is so long, cold and dry (sunlight for
few hours only)
• Available trees: pines, fir, cedar, spruce
etc (which are tinny, needle shaped with
waxy coating→to withstand cold)
• Soil get frozen during winter, few species
can survey
• Soils are acidic, prevent for further plant
grow.
• Species diversity is very low

§2.5.2. Grassland Ecosystem
• Dominated with Grass species (few trees
& shrubs)
• Rain fall in average but erratic
• Limited grazing helps to improve the
primary production of grassland,
overgrazing leads desertification.

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§2.5.2.A Tropical grassland
• Occur near the border of tropical rain forest (high average
temperature and low moderate rainfall)
• Wide variety of animals and shrubs here

§2.5.2.B Temperature grassland
• Where the place winter very cold and
summer very hot.
• Usually found on flat, gentle sloped hills.
• Soil are quite fertile can be useful for
agriculture also

§2.5.2.C Polar grassland (Arctic Tundra)
• Very cold and strong winds with ice and snow → creates harsh
condition to grow plants

§2.5.3. Desert Ecosystem
• Where evaporation exceeds
precipitation (rainfall, snow etc)
• 1/3 rd of world’s land area
• Little species diversity consist of
drought resistant plants
• Atmosphere is very dry (insulator)

§2.5.3.A Tropical desert
• Like Sahara (Africa) and Thar (India)
• Driest

§2.5.3.B Temperature desert
• Mojave in Southern California

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• Day time temperature high in summer, but cool in winter

§2.5.3.C Cold desert
• Like Gobi desert in China
• Cold winter and warm summer

§2.5.4. Aquatic ecosystem
• Water bodies. Biotic communities present in either fresh water
or in marine. In further of standing type (lentic) like ponds or
free-flowing type (lotic) like rivers.
• Pond ecosystem (stagnant):
o Receiving water in rainy season , playing key role in
villages
o Contain several types of algae, aquatic plants, insects,
fishes and birds.
o Often exposed to tremendous anthropogenic (humangenerated) pressures. (swimming, bathing, cloth washing
& drinking etc)→ get polluted
• Lake ecosystem (big freshwater bodies with standing water):
o There are several zone under the lake ecosystems
 Littoral zone: Shallow zone (not deep), where
effective penetration of sun light
 Limnetic zone: Open zone, light penetration
 Profundal zone: Deep bottom area, where light
penetration is negligible.

Rooted plants
Littoral zone
Limnetic zone
Profundal zone
(dark)

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o Contains several organisms, fishes, snails and various
type of plants etc.
o Stratification: (Arrangement of different parts/diff.
layers):
 During summer, top waters become warmer than
the bottom water →top layer only circulate without
affecting inner layer (viscous)→distinct zone

o Type of lakes:
o Highly Nutrient (NPK) concentration type, due to
agriculture run-off and municipal discharge. Eg. Dal lake
o Low pH, high humic acid and brown waters. Eg. Bog lake
o Deep lake: Ancient one; polluted
o Desert Salt lake: In arid area.
o Volcanic lake: Due to after volcanic eruption
o Artificial lake: Created due to construction of dams
• River ecosystem:
o Ist phase: high slope (mountain): Cold and clear water
rushing downward from mountain and flowing through the
plains falls in to the sea →rich in dissolved oxygen
o 2nd phase: Gentle slope : support rich growth of plants.
Less dissolved oxygen content.
o 3rd phase: Reaching sea: Bring them lot of salt and
nutrient to sea.
• Ocean ecosystem:
o Note: 70% of earth surface covered with ocean water
only. >2,50,000 marine species→serving food and drug to
humans→ also provides minerals such as iron,
phosphorus, magnesium and oil & natural gas etc
o Oceans have two major life zones

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 i. Coastal zone (land close to sea): Relatively
warm, nutrient rich and good sunlight→good for
primary production
 ii. Open sea: Deepest part of the see;
• Abundant sunlight area, good photo-synthesis
activity, sea plants here
• Dim light area
• Dark zone: ~3000 meters (3 km) deep. No
light.
• Estuary (place where river joins with sea):
o Fresh and salty water meet. Also know as transition zone.
o Strongly affected by tidal (wave) action
o Large nutrient available in that area, good for primary
production.
o Organism growing in that place (Eurythermal) has high
tolerance to temperature and salinity.
o Rich in biodiversity. Many migratory species (fishes). Half
time in sea and half in fresh water. They also get
abundant food→high productivity.
o But, Need to protect from pollution!.

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