Ecology and Environment Management

ECOSYSTEM

KEY WORDS: Biosphere, atmosphere, lithosphere, hydrosphere, ecosphere, biocoenosis,

biogeocoenosis, biome, biotic components, abiotic components, trophic structure, community

structure, food chain, trophic levels, productivity, food web, ecological pyramid, ecological

efficiency, energy subsidies , biogeochemical cycle, human modified ecosystems, ecological

succession, cybernetic.

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ECOSYSTEM

INTRODUCTION:

The earth is perhaps the only planet in the solar system that supports life. The portion of the

earth which sustains life is called biosphere. All the living organisms of the biosphere directly

or indirectly depend on one another as well as on the other physical components of the earth

that is atmosphere, lithosphere and hydrosphere (air, land and water). The atmosphere is

gaseous envelope surrounding the earth‟s surface, consisting of nitrogen, oxygen, carbon

dioxide and many other gases in very small amounts. Hydrosphere is all the water supply to the

earth which exists as liquid, vapour or in the frozen form of fresh and salt water. Lithosphere

comprises the soil and rock of the earth‟s crust. The living organisms and the nonliving

components are inter- related and interact upon each other. The term ecosphere is used to

denote biosphere (living components) along with atmosphere, hydrosphere and lithosphere

(nonliving component) of the earth as one entity. In fact ecosphere is the largest worldwide

ecosystem. Ecosphere is very huge and can not be studied as a single entity. It is divided into

many distinct functional units called ecosystem.

ECOSYSTEM

An ecosystem is an interacting unit of biotic (living) and abiotic (non-living) components at a

given place so that a flow of energy leads to clearly defined trophic structure, biotic diversity

and material cycle. It is a natural functional unit to study ecology. A.G. Tansley (British Ecologist) proposed this term for the first time in 1935. The concept of oneness of interacting

living organisms with their nonliving environment with different names is very old in the

history of mankind. In 1877 Karl Mobius studied the oyster community and called it

biocoenosis (Germany). An American naturalist S.A. Forbes (1887) studied lake system and

named lake as a microcosm. The term biocoenosis was also proposed by G.F. Morozov for

the forest system. This term was later expanded to biogeocoenosis (or geobiocoenosis ) by

Sukachev in 1944. In English language the term ecosystem is preferred, in German

biogeocoenosis or geobiocoenosis is more commonly used. Whatever the term may be but the

concept of ecosystem is very broad. It can be as big as the entire ecosphere, a tract of forest,

lake, pond or meadow (grassland). The laboratory cultures are also very small ecosystems and

may be called microecosystem.

Another term biome was introduced by Victor Shelford. It is a broad natural plant

formation with its associated animals. For example, deciduous and coniferous forests and

desert types of biomes that are characterized by a uniform life form of vegetation such as

coniferous or deciduous trees or xerophytic plants respectively. Physical and geographical

factors such as rainfall, temperature and soil type determine the nature of these vegetation

zones. These climatically and geographically distinct zones, differentiated primarily on the

basis of the types of plants that grow in these regions are called biomes. They are found in small

patches, widely separated from each other and give a beautiful kaleidoscopic appearance to the

planet earth from a distance. For example deserts are found in India, Africa, Australia and

elsewhere under similar arid condition of high temperature and low precipitation and make one

type of biome known as desert. In other words large ecosystem are called biomes. A pond or

a lake is an ecosystem whereas, freshwater is a biome since both of them support plants which

can survive in freshwater. Animal life depends upon plants therefore, both the ecosystems

support freshwater species of plants and animals (Freshwaters have very low or no salts and are

continuously cycling through water cycle).

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COMPONENTS OF AN ECOSYSTEM

I Components of an ecosystem :

(A) Abiotic

(B) Biotic

(A) Abiotic Components (nonliving): Fig.1 They can be classified into following three

categories

1. Physical factors: They are light, temperature, humidity, pressure and soil profile.

These factors sustain and control the growth of organisms in an ecosystem. Deficiency

or excess of any one of them limits the growth of the organisms in the ecosystem

2. Inorganic substances such as carbon, carbon dioxide, nitrogen, oxygen, phosphorus,

sulphur, zinc, water and many other minerals. These substances make the

micronutrients and macronutrients and are converted into the living biomass by the

plants. The essential inorganic elements such as carbon, hydrogen, nitrogen,

phosphorus calcium and potassium which are required in large quantities are called

macronutrients. The essential elements required in small amounts are the

micronutrients e.g. zinc, boron and magnesium. Sources of all nutrients for plants are

air, water and soil.

3. Organic Compounds: Carbohydrates, proteins, lipids and humic substances are the

organic substances in an ecosystem. They are the complex molecules and out side the

organism they make the abiotic component, but in the living organism they make an

important component of the biomass .

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- - - ------... -- .,...

.._.

RESPIRATOI N

_.._. ----- -- --...... -r

co" I > 02. I >

H o r >

NUTRIENTS

DECOMPOSERS

DEAD REMAINS

I EXCRETOTY WASTES

t....----- -·- - ------1 COMPONENTS OF AN ECOSYSTEM

Fig.l Biotic and abiotic components of an ecosystem.

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(B) Biotic Components (living)

1. Producers or Autotrophs: The green plants produce food for the entire ecosystem by

the process of photosynthesis (“Auto”- self “troph” nourish). They absorb nutrients

from the soil, carbon dioxide from the air and capture solar energy for this process.

Since they perform the function of food production for the entire ecosystem they are

also known as producers.

2. Heterotrophs: (“Hetero”- others “trophs”-nourish) They are also called consumers

and they consume the food synthesized by the autotrophs. First level consumers are

called herbivores (e.g.cow,deer and rabbit ) and they feed directly on autotrophs.

Herbivores are the key industry animals because they convert the plant material into

the animal material. Carnivores are the animals which feed upon other animals. The

carnivores which feed directly on herbivores are called primary carnivore (e.g. frog,

birds and cat) and those which feed on other carnivores are known as secondary

carnivores (tiger, lion and dogs ).The animals feeding on both plants and animals are

known as omnivores like human, pig and bear. Other special feeding groups are such as

parasites and scavengers. Parasites are specialized in spending a part of their life or

complete life on the other living organism called host which can be a plant or animal.

They may result in some disease in the host or lead to its complete death. Scavengers eat

the dead animals or plants, e.g.crow, vultures and gulls. Plant scavengers are termites

and beetles that feed on dead and decaying wood.

3. Decomposers: The decomposers are special type of consumers and depend on the dead

remains of animals and plants.They are also called detrivores or detritus feeders. These

are small organism (microdecomposers) mostly bacteria and fungi that break down the

complex dead organic matter of plants and animals into the simple molecules by

secreting enzymes outside their body (saprotrophs). They partly absorb these for their

own metabolism and release the rest into the medium for the use of autotrophs. Thus

they play a very important role in recycling of the nutrients (biogeochemical cycles).

There are some macrodecomposers like worms, beetles, snails, millipedes and

earthworms which help in chopping the dead remains into very small pieces so that they

can be finally decomposed by microdecomposers. Macrodecomposers are also known

as reducer decomposers as they ingest the detritus , break it down into smaller pieces

mix it with the substrate, excrete it, spread the fungal spores and stimulate microbial

growth to facilitate decomposition. They also consume microdecomposers associated

with detritus.True decomposers are bacteria and fungi.

STRUCTURE OF ECOSYSTEM

The structure of an ecosystem is characterized by its physical organization of the biotic and

abiotic components. The major structural features are :

• Trophic organization ( or Trophic structure)

• Species composition( or community structure)

• Stratification

(i) Trophic organization: Trophic (related to food) organization of an ecosystem

represents the feeding relationships of its organisms. The feeding relationships between

the various biotic components can be studied as food chains, food webs and

standing crops.

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Food Chain: Transfer of food from the plants (producers) through a series of

organisms with repeated eating and being eaten is called food chain e.g.

Grasses Grasshoppers Frogs Snakes Hawk / Eagle

Some more examples of food chain are given in fig 2.

Fig. 2: Examples of food chain in grassland, pond and forest ecosystem.

Each step in the food chain is called trophic level. In the above example grasses are first and

eagle/hawk represents the fifth (and fourth in first figure of pond ecosystem) trophic level.

Two important things you can note in these chains are:

• Weaker organisms are attacked by the stronger organisms.

• The number of organisms reduces at each step but the size of organisms increases.

• The number of steps in a food chain is limited to 4 -5.

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A food chain consists of the following trophic levels :

1) Autotrophs (Producers): They produce the food for all other organisms of the ecosystem.

Autotrophs represent the first trophic level of the food chain. They are largely green plants

and convert inorganic substances by the process of photosynthesis into food (organic

molecules) in the presence of sun light. The total rate at which the radiant energy is stored by

the process of photosynthesis in the green plants is called Gross Primary Productivity

(GPP). This is also known as total photosynthesis. A part of the gross primary productivity is

utilized by the plant for its own metabolism, maintenance and reproduction. For all these

processes the energy is produced by plant through respiration which is converse of

photosynthesis. The remaining is stored in them as Net Primary Productivity (NPP) and is

available to the consumers.

GPP = NPP + R or GPP –R = NPP

Productivity in the biological system is a continuous process but it varies from place to place

and with time. Therefore, it is essential to designate it with a space and time unit e.g. gm/m2/day

or cal /m2/day. The net primary productivity accumulates over a given period of time as plant

biomass at a given place and is referred to as standing crop. This can also be expressed in units

of mass or energy as gm/m2

or cal/ cm2 .

Standing crop is the amount of biomass or energy present at any given time whereas, productivity is the rate at which organic matter is produced by photosynthesis in the ecosystem.

The total production of the plant is distributed in a very systematic way to its various parts.

How much of productivity is allocated to each part, is a function of the life form of the plants

well as the environmental conditions as explained below:

i During different growth phases: Sixty percent of the products of photosynthesis are

allocated to leaves during the period of growth. This is reduced to 10 to 20 % by the

time the seeds are ripe. When in bloom, the plant allocates 90% of its productivity to the

flower head and the remainder to the leaves, stem and roots. In case of trees and woody

shrubs early in the life leaves make up more than one half of their biomass (dry weight)

but as the trees age they accumulate more biomass in stem and trunk (as woody tissue)

which become thicker and heavier. The ratio of the leaves to the woody tissue changes.

Eventually it is left to 1% to 5% of the total mass of the tree. The leaf biomass (producer

component) is considerably less than the biomass supported by it.

ii Availability of nutrients: The ratio of the distribution of net production to above ground

and below ground is also an important characteristic of the ecosystem. Low light

condition favours the allocation of energy to the production of leaves and stem at the

expense of roots. A reduction in the nutrients and water availability promotes the growth

of the root system at the cost of stem and leaves. As a result of this the ecosystems that

are associated with low rainfall or low soil fertility have a lower root / shoot ratio than

those growing in the better rainfall and nutrient rich soils. In the forest ecosystem the

different components of the forest exhibit different patterns of above ground and below

ground allocation of net production.

iii Topographical variations: Productivity in the terrestrial ecosystems is greatly

influenced by the climate of the region. This is clear from the following table showing

the net primary productivity and biomass of a few ecosystems.

In the oceans, the costal regions and the coral reef are most productive for two reasons.

Firstly, in both of them the water is shallow that results in greater transport of materials

to the surfaces. Secondly the coastal regions receive a large input of nutrients carried

from the terrestrial ecosystem.

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Name of the ecosystem Mean net primary

productivity

G /m2

/yr

Mean biomass

Kg/m2

Tropical rain forest 2000.0 44.00

Temperate evergreen forest 1300.0 36.00

Temperate deciduous forest 1200.0 30.00

Boreal forest 800.0 20.00

Savanna 700.0 4.00

Desert 71.0 0.67

Swamp and marsh 2500 15.00

Table1: Showing primary productivity and biomass of some terrestrial ecosystems (Ref: ecology and Field biology

by Smith )

(iv) Diurnal and seasonal variations: Primary production varies with time of the day and

season of the year. In the cold winters and dry season the plants become dormant and

the productivity ceases. In the tropical forests there are no seasonal variations in the

primary productivity due to the constant environmental conditions.

(v) Age of the plant: Age of the plants is also very important in determining the net

primary production of an ecosystem e.g. as the age of a forest increases most of the

living biomass is in the woody tissue of the tree and the gross primary production is

used up in their maintenance and very little is left for the growth.

2) Herbivores: These are animals which feed directly on the plants. They are first level

consumers and therefore, they are also known as primary consumers and make the

second trophic level in the food chain e.g. insects, birds, rodents and ruminants.

Herbivores are capable of converting energy stored in the plant tissue into animal tissue.

Therefore, they are also known as key industry.

Adaptations of herbivores

• They can digest high cellulose diet. They have symbiotic cellulose digesting bacteria

in their alimentary canal. These microorganisms can synthesize the enzyme

cellulase which can digest the plant cell wall that is made up of cellulose. So that the

plant cell contents can be released for their digestion by the digestive enzymes of the

herbivore. Bacteria also synthesize vitamins B complex and essential amino acids for

the herbivore.

• Teeth of the herbivores are modified to cut and chew the leaves.

• Stomach of ruminants is four chambered namely, rumen, reticulum, omasum and

abomasums. The hurriedly chewed food enters into the first and second chamber

(rumen and reticulum). Here water is added to food, it is kneaded by the muscular

action and fermented by the bacteria into a soft pulp. The bacteria convert cellulose,

starch and sugar into fatty acid which is absorbed as a source of energy. The coarser

material reenters the rumen for further fermentation. Finer material enters the

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reticulum and then it goes to omasum and abomasums. Abomasum is the true

glandular stomach. At leisure the undigested food is regurgitated (cud)), chewed

again more thoroughly and passed down.

• In case of lagomorphs (rabbit, hare and pikas) faecal pellets are reingested. This

process is known as coprophagy. The reingested faecal pellets are rich in proteins

and have low fibre content. This provides them with the vitamin B synthesized by

bacteria and partly digested food.

3) Carnivores: Carnivores are the animals that feed on other organism or its tissue. They are

the third (as well as the fouth in some) trophic level. They are secondary level consumers if

they feed on herbivores and tertiary level consumers if they use other carnivores as a

source of their food. Frog, dog, cat and tiger are carnivores. Generally carnivores are larger

than the organism that they feed upon.

Adaptations of carnivores:

• Carnivores have well developed canines for biting, piercing and tearing the flesh of the

animals. Cheek teeth are reduced but many species have sharp crested shearing or

carnassial teeth.

• They are very ferocious. As the feeding level of the carnivore increases its fierceness

and size increases

• Their sense of smell and hearing is well developed.

• Hawks and owls have sharp talons for holding the prey and also their beak is hooked

for tearing the flesh.

• The alimentary canal is shorter than that of herbivores.

• They have higher ecological efficiencies.

• The energy stored by them is finally utilized by decomposers after their death.

4) Decomposers: They make up the final trophic level in a food chain. True decomposers are

the organisms that feed on dead organic matter called detritus. They take care of the dead

remains of organisms at each trophic level and help in recycling of the nutrients.There are

two types of decomposers namely microdecomposers and macrodecomposers.

Microdecomposers are very small microcopic organisms like bacteria, fungi, and

protozoans. Macrodecomposers make a very small fraction of the decomposers and are

visible to the naked eye. They are springtails, mites, millipedes, earthworms, nematodes,

slugs, crabs and many larval forms.

Special feeding groups

5) Omnivores: Omnivores consume both plants and animals as source of their food e.g. human

beings. Some of the omnivores like the red fox feed on berries, small rodents as well as on

dead animals. Thus it is a herbivore, carnivore and scavenger.

6) Scavengers: These are the animals that feed on the dead plants and animals e.g. termites and

beetles many marine invertebrates feed on the decaying wood and are called plant

scavengers. Vultures, gulls and hyena are some examples of animal scavengers.

7) Saprophytes: These are the plants that feed on the dead animal and plant material. These

plants do not photosynthesize, therefore they can live under deep shade or in dark caves

where light is not available to them.

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CARNIVORES CARNIVORES

DECOMPOSERS HERBIVORES

DETRITUS PRIMARY NET

PRODUCTION

CARNIVORES CARNIVORES

DECOMPOSERS HERBIVORES

DETRITUS PRIMARY NET

PRODUCTION

CARNIVORES CARNIVORES

DECOMPOSERS HERBIVORES

DETRITUS PRIMARY NET

PRODUCTION

CARNIVORES CARNIVORES

DECOMPOSERS HERBIVORES

DETRITUS PRIMARY NET

PRODUCTION

Types of food chains

Two major types of food chains are identified in any ecosystem namely grazing food chain

and detritus food chain. The grazing food chains begin with the living plant biomass (net

primary production) and the detritus food chain with the dead organic matter (detritus ) as the

source of energy. In both the food chains carnivores feed upon the herbivores. In any ecosystem

the two chains are sharply separated. and make a Y shaped food chain. The two channel Y

shaped energy flow model is more practical than a single channel because of the following

three reasons:

• It conforms to the basic stratified structure of an ecosystem.

• Direct consumption of the living plants and utilization of dead organic matter is usually

separated in both time and space.

• Macroconsumers (phagotrphic) organisms and microconsumers (decomposers) differ

greatly in size-metabolism relation. In the marine ecosystem the energy flow via the

grazing food chain is larger than the detritus food chain, whereas the reverse happens

in a forest ecosystem.

CARNIVORES CARNIVORES

DECOMPOSERS HERBIVORES

DETRITUS PRIMARY NET

PRODUCTION

AUTOTROPHS

Fig. 3: Y shaped food chain showing separated detritus and grazing food chains.

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Food web: Food chains in the ecosystem are not linear rather they are interconnected with one

another. A network of food chains which are interconnected at various trophic levels so as to

form a network of feeding connections in a community called a food web (Fig.4)

.

SOLAR RADIATIONS

PHYTOPLANKTON

(Algae,Diatoms,)

ZOOPLAKTON

(Daphnia,Cyclops)

BLOODWORMS

(Chironomids )

ADULT INSECTS

EMERGE OUT

SUNFISH

(Lepomis)

ADULT INSECTS

EMERGE

OUT

PREDACEOUS

(Dipteran larvae)

BASS

(Microptrerous)

TERRESTRRIAL

INSECTS

MAN

Fig 4:.4 Simple food web in a pond ecosystem

In this example sunfish feeds upon Daphnia, Cyclops or bloodworms and may be a food for

several other fishes in the pond. Thus in a food web one animal may be a member of several

different food chains. Food webs are more realistic models of energy flow through an

ecosystem.

Significance of food chain

• Ecosystem sustainability: An equilibrium between the producers, consumers and

decomposers is important for the sustainability of the ecosystem. Producers absorb the

solar energy for the ecosystem to synthesize food. The consumers use this food for their

own survival, growth and reproduction and the decomposers help in recycling of the

chemical nutrients.

• Food chains determine the trophic structure of ecosystem:Producers in all the

ecosystems make the first trophic level. Primary production of the autotrophs

determines the kind and number of heterotrophs in the ecosystem.

• Energy flow through ecosystem: Food chains explain the flow of energy and circulation

of materials in an ecosystem. They help in understanding the feeding relations and

interaction of different organism living together in any ecosystem.

• Ecosystem balance: Food chains are essential in maintaining the ecosystem balance and

are interconnected to make food web in natural ecosystems. Large ecosystems have

more complex food webs and are more stable.

• Biomagnification of pesticides and insecticides: The pollutants get concentrated

through the food chain, as the living organisms do not metabolize them.

Biomagnifications is a man-induced process, which brings input of non-degradable

pollutants into food chain. Their concentration goes on increasing at each higher

trophic level. For example, DDT is widely used as a pesticide to kill harmful insects. It

lasts for nearly 20 years (long half life). It is used in 0.02-ppm in water to control

insects and its concentration increases to a fatal level in large aquatic birds through

food chain.(Fig.5).

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Fig. 5: Biomagnification of pesticides in a food chain.

Standing crop: Standing crop is the amount of living matter at any given time in an ecosystem.

It can be expressed in terms of biomass, number or total amount of energy fixed at each step of

the food chain. It gives a definite trophic structure to the ecosystem. Graphically it is

represented with the producers at the base and the subsequent trophic levels as the tiers. This

gives a gradually sloping pyramidal shape as the biomass, number and energy is reducing at

each trophic level. This graphical representation of the standing crop expressed as number,

biomass or energy is called ecological pyramid.

• Pyramid of number: For example in grassland you have observed that the number of

grasses is more than the total number of herbivores (grasshoppers and hare) that

feed on them (Fig.6 A) and the number of herbivores is more than the number of

snakes and birds (carnivores). When an ecological pyramid is constructed on the

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basis of the number of individuals at each trophic level it is called a pyramid of

number. The pyramid of number is a result of three phenomenon

(i) Geometrical - many small units are required to build up one big unit (units

are organisms).

(ii) Entropy -due to entropy at each step many small organisms are required to

support a few large organisms, which is a basic principle of food chains.

(iii) Inverse size metabolism pattern - smaller organism have higher metabolic

rate than the larger organisms.

Some times the pyramid of number is inverted. For example many caterpillars and insects

feed on one plant/ tree. In this case, the number of herbivore is more than the number of

autotroph. Similarly the number of phytoplankton is less than the herbivorous zooplankton in

English channel. This is because of the high turn over rate of phytoplankton in it.

• Pyramid of biomass: (Fig. 6 B) The graphical representation of biomass at each

trophic level . For instance the total biomass of trees in the forests is greater than the

total biomass of the herbivores supported by them. At the level of top carnivore in a

community very little biomass is left to support any further trophic level. Pyramid of

biomass can also be inverted like the pyramid of number. In a channel of water or a

canal where the producers have short life cycles and are replaced rapidly by the new

plants (high turn over rate) the biomass of producers is less than consumers who

have longer life span like fishes. Pyramid of biomass is expressed as dry weight

per unit area.

C3-1.5 C3-21

C2 – 1,20,000

C1-1,50,000

P-200

C2-90,000

C1-2,00,000

P-1,50,000

C1-37

P-809

C2-11

C2-383

C1-3,308

P-20,810

FOREST GRASSLAND GRASSLAND LAKE

Pyramid of Number ( Number/m

2

Pyramid of Biomass

( gm/m2

Pyramid of Energy

( K.cal./m2/yr)

A B C

Fig. 6(A) Pyramid of number, (B) pyramid of biomass and ( C) pyramid of energy.

• Pyramid of Energy: (Fig. 6C) The pyramid of energy represent the total amount of

energy fixed at each trophic level. These give the true functional structures to the

ecosystem. They are never inverted and most informative. Energy is expressed in

terms of rate such as kcal /unit area /unit time or cal /unit area/unit time. As shown in

the figure in a lake ecosystem, the energy at producers level is 20,810 herbivore is

3,308 primary carnivore is 383 and secondary carnivore is 21 kcal /m2

/year. Energy

pyramid provides a more suitable index for comparing any or all components of an

ecosystem. The pyramid of number overemphasizes the smaller individuals, biomass

gives more importance to the larger individuals and therefore, both can not be used as

reliable tools for comparing the functional role of the populations that differ widely

in size and metabolism.

ii) Species composition (community structure): A community is an assemblage of many

populations that are living together at the same place and time. A tropical forest community

consists of trees, vines, herbs and shrubs along with large number of different species of

animals. This is known as species composition of the tropical forest ecosystem. Each ecosystem

has its own species composition depending upon the suitability of its habitat and climate. If you

compare animals and plant populations of a forest they are entirely different from that of a grass

land. Not only the types of species are different in these two ecosystems even their total

number and biomass is also different A forest ecosystem supports much more number of

species of plants and animals than a grassland. The total number and types of species in a

community determine its stability and ecosystem balance (ecosystem equilibrium).

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iii) Stratification: The vertical and horizontal distribution of plants in the ecosystem is called

ecosystem stratification. The plants are of different heights in the forests. Tallest trees make

the top canopy. This is followed by short trees and shrubs and then the forest floor is covered

with herbs and grasses. Some burrowing animals live underground in their tunnels or on the

roots of the plants. Each layer from the tree top to the forest floor has different fauna and flora

from the other. This is termed as vertical stratification of forest ecosystem. On the other hand,

desert ecosystem shows discontinuous layers of scant vegetation and animals with some bare

patches of soil showing a type of horizontal stratification .

FUNCTIONS OF AN ECOSYSTEM

Ecosystems are dynamic in nature. They perform some functions to keep them in a state of

equilibrium. These are also being designated as properties of an ecosystem and are as follows:

1. Energy flow

2. Nutrient cycles (biogeochemical cycles)

3. Development of ecosystem or ecological succession

4. Homeostasis or feedback control mechanisms

1. Energy Flow through an Ecosystem

The energy enters into the ecosystem in the form of solar radiation and is converted into food

(plant biomass) by the producers. Food stored by the plants and their biomass (matter) is the

chemical form of energy. From the producers the energy passes through various trophic levels.

This process of transfer of energy through various trophic levels of the food chain is known as

flow of energy. All the functions of ecosystem depend on the flow of energy through it and

follow the laws of thermodynamics like in any other physical system. In Fig. 7 boxes represent

the trophic level and the pipes depict the energy flow in and out of each trophic level. The

quantity of energy flowing through the successive trophic levels decreases as indicated by the

reduced size of the boxes and thickness of pipes in the figure. This is because all the energy

entering at each trophic level is not used for production of biomass due to two reasons. Firstly,

a part of the energy is lost (not utilized) according to second law of thermodynamic in the

process of transfer of energy from one level to another due to entropy. Secondly, a part of it is

used up by the organisms for their own metabolism through the process of respiration. If

herbivores consumes 1000 kcal. of plant energy in the form of food, only 100 kcal. is converted

into herbivore tissue,10 kcal. into first level carnivore and only 1 kcal into second level

carnivore. This is known as10 % law (or ecological rule of thumb) where by only 10 % of the

energy is transferred to the next higher trophic level.

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Herbivores

R

R

SOLAR NU RADIATIONS

NU

NU

NU NU

Autotrophs Prim. Carnivores

Sec.

Carnivores

Decomposers

R R

LIGHT R REFLE CTED

10,000 Kcal 1000 Kcal 100 Kcal 10 Kcal

Figure 7: Model of energy flow through an ecosystem. Boxes indicate the standing crop biomass and pipes

indicate the energy flowing (NU = Not utilized, R = Respiration).

. The entire process of energy flow can be summarized in the following four steps

• The flow of energy in an ecosystem is always linear or one-way

• It follows the ecological thumb rule of 10%.

• The number of steps is limited to four or five in a food chain for the transfer of

energy because during this process of transfer of energy some energy is lost into the

system as heat energy (second law of thermodynamic) and is not available to the

next higher trophic level

• At every step in a food chain the energy received by the organism is also used for its

own metabolism and maintenance. The left over is passed to next higher trophic

level.

ECOLOGICAL EFFICIENCY

Ecological efficiency is defined as the percentage ratio of the energy flow at different points

along the food chain. Commonly if a poultry man speaks of 30 % efficiency .in his poultry

farm. Thus efficiency for him is the percentage ratio of input (feed) to the output in chicken

(biomass).

The ecological efficiency can be given in terms of various parameters such as growth,

production and assimilation. Lindman in 1942 defined these ecological efficiencies for the first

time and proposed 10% rule as discussed in energy flow model. However, there are slight

variations to this law in different ecosystem and ecological efficiencies may range from 5 to

35%.

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Ecological efficiency is also called Lindman‟s Efficiency and can be represented as:

Production efficiency = P = PRODUCTION X 100

A ASSIMILATION

( Similarly assimilation efficiency is percentage conversion of food into protoplasm)

In the above mentioned example if 10 gm. food is given to the chicken its biomass would increase by 3 gm.

Therefore, 3 x 100 = 30 % is the production efficiency.

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This is an example of human modified system and also it is assumed that all the food is

assimilated in the body of chicken. In natural ecosystems this efficiency will be much less.

Ecological efficiency increase at higher trophic levels. Ecological efficiency can be given as

production efficiency, assimilation efficiency, growth efficiency or tissue growth efficiency.

BIOGEOCHEMICAL CYCLES

The cycling of the nutrients in the biosphere is called biogeochemical or nutrient cycle ("Bio"-

living, "Geo” -rock, “Chemical‟ –element ). There are more than 40 elements required for the

various life processes by plants and animals. These elements are continuously cycling in the

ecosystem. through the biogeochemical cycles and the planet earth has no input of these

nutrients. This is in contrast to the flow of energy which is linear and there is a continuous

input of solar radiation into the biosphere. . This is because energy is utilized by the organisms

to perform their life processes whereas, the nutrients (matter) from the dead remains of

organisms are recovered and made available to the producers by decomposers.

There are two important components of a biogeochemical cycle :

1) Reservoir pool: The large store of nutrients is called a reservoir pool. Rocks and

atmosphere make reservoir pool. The nutrients are stored here for a longer duration.

2) Cycling pool : Plants and animals make the cycling pool. They are relatively short-

term stores as the nutrients are continuously moving in them through the food chain.

On the basis of the type of reservoir these cycles are classified into two types

1) Sedimentary cycles: In these cycles main reservoir is rock or soil (lithosphere), e.g.

sulphur and phosphorus cycle.

2) Gaseous cycles. Atmosphere is the main reservoir in the gaseous cycles. Those

nutrients that have a prominent gas phase, e.g. nitrogen and carbon show this type of

cycle. The nutrients are replaced in them as fast as they are utilized.

CARBON CYCLE

Carbon cycle is important for sustainability of the biosphere for following two main reasons

:

• Carbon is the basic constituent of all organic molecules of the living organisms.

• It helps in fixing the solar energy for the entire ecosystem by the process of

photosynthesis.

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Atmospheric carbon dioxide is the source of all carbon in both living organisms as well as in

the fossils (used as fossil fuel). It is highly soluble in water. Oceans also contain large quantities

of dissolved carbon dioxide and bicarbonates.

The carbon cycle comprises the following processes:

Photosynthesis: Terrestrial and aquatic plants utilize CO2 for photosynthesis. Through this

process of photosynthesis the inorganic carbon is converted into organic matter in the presence

of sunlight and chlorophyll. The carbon dioxide is thus fixed and assimilated by plants.It is

partly used by them for their own life processes and the rest is stored as their biomass which

is available to the heterotrophs as food.

Respiration: It is the essential life process for all living animals, plants and decomposers.

Respiration is a metabolic process reverse of photosynthesis in which food is oxidized to

liberate energy (to perform the various life processes) and carbon dioxide. Thus the carbon

dioxide of the atmosphere is recovered through this process.

Decomposition: All the food synthesized and assimilated by plant or animals is not metabolized

by them completely. A major part is retained by them as their own biomass which is available

to the decomposers on the death of these organisms. The organisms the decomposers break

down the dead organic matter and release the left over carbon back into the atmosphere.

Combustion: Fossil fuel on burning releases carbon dioxide and carbon monoxide into the

atmosphere. Forests make a large amount of fossil fuel. Fossil fuel is product of complete or

partial decomposition of plants and animals as a result of exposure to heat and pressure in the

earth’s crust over millions of years. They occur as crude oi, coal , natural gas or heavy oils

Forests also act like carbon reservoirs as the carbon fixed by them cycles very slowly due to

their long life. They release CO2 by forest fires.

Impact of human activities: Carbon dioxide is continuously increasing in the atmosphere due

to human activities such as such as industrialization, urbanization and increased use of

automobiles. These anthropogenic activities are resulting in global warming and climate

change due to increased CO2 concentration.

ATMOSPHERIC GREEN PLANTS

CO2 Make Organic Compounds

ANIMAL

TISSUES

FOSSIL FUEL

GAS,

PETROLEUM,

COAL

Fig. 8 Carbon cycle: Arrows indicate the processes of the carbon cycle and compartments are the sites of these

processes or the store houses of carbon in the reservoir pool and ecosystem .

NITROGEN CYCLE

Nitrogen is an essential constituent of proteins, which are the building blocks of all the living

beings.

Our atmosphere contains nearly 79%of nitrogen but it cannot be used directly by the majority of

living organisms. It is converted into some chemically usable form that comprises the major

function of the nitrogen cycle. There are five main processes on the basis of which the entire

nitrogen cycle can be explained.

(I) Nitrogen fixation: This process involves conversion of gaseous nitrogen into

ammonia or nitrates which can be used by plants. It involves the following two

steps:

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1) Activation: Activation of nitrogen this requires 160 kcal of energy for fixation of

each mol of nitrogen (28 g) and the molecular nitrogen is converted into atomic

nitrogen.

N2 2N

2) Fixation: Activated nitrogen combines with hydrogen to form ammonia. In this

step per mol synthesis of ammonia liberates 13 kcal of energy.

2 N + 3H2 2NH3

Atmospheric nitrogen can be fixed by the following three methods.

i) Atmospheric fixation: Lightening, combustion and volcanic activity help in the

fixation of nitrogen

With this method of fixation atmospheric oxygen and nitrogen combine to form

nitrate which comes to the earth with rain as nitric acid. Nearly 8.9 kg. N /ha is

brought to the earth by high energy fixation.

ii) Industrial fixation: At high temperature, 4000

C and high pressure 200

atmosphere., molecular nitrogen is broken into atomic nitrogen which then combines

with hydrogen to form ammonia.

iii) Bacterial fixation: This is also known as biological fixation of nitrogen and makes

up 100 to 200 kg.N/ha. Thus 90% of the fixed nitrogen to the earth is contributed by

this method every year. There are two types of bacteria that help in biological

fixation of nitrogen.

Symbiotic bacteria e.g. Rhizobium on the root nodules of leguminous

plants fix the nitrogen for these plants. Rhizobium are aerobic and non spore

forming rod shaped bacteria.

Free living or symbiotic. Azobacter (aerobic ), Clostridium1 (anaerobic)

and blue green algae like Nostoc and Calothrix are also important nitrogen

fixers on land and in water. They can combine atmospheric or dissolved

nitrogen with hydrogen to form ammonia.

Free living and the symbiotic bacteria both require molybdemun as an activator. An

accumulation of ammonia and nitrates in the soil inhibits the activity of these bacteria.

3) Nitrification: It is a process by which ammonia is converted into salts of nitrate or

nitrite by Nitrosomonas and Nitrococcus bacteria respectively. Energy is liberated in

this step. Another soil bacteria Nitrobacter can covert nitrate into nitrite

Nitrococcus Nitrococcus

NH3+11/2O2 HNO2+H20+165kcal H + NO2

4) Assimilation: In this process nitrogen fixed by plants is converted into

protoplasmic organic molecules such as proteins, DNA and RNA. These molecules

make the plant and animal tissue

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5) Ammonification: In this process amino acids are broken down into ammonia

with the release of energy by the decomposers. Living organisms produce

nitrogenous waste products such as urea and uric acid. These waste products as well

as dead remains of organisms are converted back into inorganic ammonia by the

ammonifying bacteria. This process is called ammonification. Ammonia can be

directly incorporated into amino acids by the plant roots.

6) Denitrification: Conversion of nitrates back into gaseous nitrogen is called

denitrification. It is facilitated by fungi and bacteria, (Psuedomonas). Denitrifying

bacteria live deep in soil near the water table since they like to live in oxygen free

medium. Dentrification is reverse of nitrogen fixation.

Fig.9: Nitrogen cycle in nature.

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WATER CYCLE

This is also known as hydrological cycle. Earth is a watery planet of the solar system but a very

small fraction of this is available to animals and plants. Water is not evenly distributed

throughout the surface of the earth. Almost 95 % of the total water on the earth is chemically

bound to rocks and does not cycle. Out of the remaining 5%, nearly 97.3% is in the oceans and

2.1% exists as polar ice caps. Thus only 0.6% is present as freshwater in the form of

atmospheric water vapours, ground and soil water.

Solar radiation and earth‟s gravitational pull are the main driving forces of water cycle.

Evaporation, condensation and precipitation are the main processes involved in water cycle.

These processes alternate with each other.

Water from oceans, lakes, ponds, rivers and streams evaporates by sun‟s heat energy. Plants

also transpire huge amounts of water through their leaves. Water remains in the vapour state in

air and forms clouds, which drift with the wind. Clouds meet with the cold air in the

mountainous regions above the forests and condense to form rain, which falls due to gravity.

EVAPORATION FROM OCEANS, EARTH AND LEAF SURFACE

FORMATION OF CLOUDS

PRECIPITATION

SURFACE RUN OFF AND ACCUMULATION AS GROUND WATER

SREAMS AND RIVERS RUN OFF INTO OCEAN

PLANTS

TRANSPIRATION EVAPORATION

Fig. 10 : Water cycle.

On an average 84% of the water is lost from the surface of the oceans by evaporation. While

77% is gained by it from precipitation. The remaining 7% of the ocean evaporation is balanced

by water run off through the rivers from the land that is because on land evaporation is 16%

and precipitation is 23%.

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GROWTH OF AN ECOSYSTEM OR ECOLOGICAL SUCCESSION

In an ecosystem the process of gradual and orderly replacement of plants and animals of an

ecosystem till a relatively stable community is established is known as ecological succession or

growth of an ecosystem. It is a continuous and directional process. The ecosystem has a

definite species composition at a given time and place. The species composition of the

communities is not stable but undergo regular changes in a definite manner with time until it

becomes more or less stable. It can also be compared to the growth of an individual in which

changes can be observed up to its adulthood and then apparently there is further no change.

Imagine a barren land or an igneous rock where life has never existed before. It is very poor in

nutrients. Succession starts with weathering of rock by wind, sun and temperature so that it can

be invaded by very primitive forms of life such as lichens. After some time the land becomes

more suitable for the growth of next higher forms of life and the lichens are replaced by

mosses. This process continues in the following sequence.

Uninhabited barren rock lichens mosses annual herbs

perennial herb shrub pines forests.

Each step of succession is known as a seral stage and the entire sequence is called sere It

finally results in a stable and complex community called climax. Lichens make the first seral

stage and are called pioneer community.

Forest is of the last seral stage which is stable for a very long time and it represents a climax

community. The climax community of a place depends on the climatic conditions of that

region. If it is moist climate it results in the formation of forests but if it is dry, the climax

community may be a grass land or a desert.

Primary and secondary successions: The succession which takes place on a bare rock (like

igneous rock) where life has never existed earlier is called primary succession. Secondary

succession occurs on places where the organisms were living at one time and suddenly they

disappeared due to fire, floods or some other natural calamity. This land is rich in nutrients

therefore; complex higher groups like grasses or pine trees can begin to grow on such places.

Succession is also classified as autogenic and allogenic based on the cause of change. It is

called allogenic if it results from natural changes in the physical environment and autogenic if it

is caused by modification of the environment by the community itself. In the natural ecosystem

both the forces work together.

HOMEOSTASIS OF THE ECOSYSTEM

The term homeostasis (“homeo” –same “static”- standing) implies a state of equilibrium in

ecosystems. By virtue of this process most of the biological systems have a tendency to

maintain stability. Stability is the tendency of an ecosystem to reach and maintain an

equilibrium of either a steady state or stable oscillations. Disturbances in an ecosystem can be

internal or external. Internal disturbances are changes in the species composition and number.

For example in a pond ecosystem if the population of zooplankton is increased, they would

consume large number of the phytoplankton as a result there would be short supply of food to

them after some time. As their number is reduced because of starvation, phytoplankton start

increasing and after some time the population size of zooplankton also recovers. Similar

process occurs at all other trophic levels in the community.

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Large No of Phytoplankton

Increase population of Zooplankton

due to excess food available

Reduction in Phytoplankton

Population of Zooplankton decrease

due to starvation

Population of Phytoplankton

starts increasing due to their less consumption

Fig. 11.: Homeostasis in lake ecosystem

Ecosystems exhibit resistance and resilience. Resistance is a measure of the degree to which a

system is changed from an equilibrium state following a disturbance. Resilience is the speed

with which a disturbed ecosystem returns to the state of equilibrium. Mature ecosystems are

more resistant to any change e.g. a forest is more resistant to change than any of its seral stage.

Earth’s biosphere, atmosphere, hydrosphere and lithosphere together make up a feed back

system that maintains an optimal physical and chemical environment for life on earth. The

feed back is not possible without the buffering action of life on earth No control mechanism

from out side the planet has been discovered. Microorganisms are only life forms that could

function like a chemostat and help in maintaining 21% of the atmospheric oxygen which is

essential for life on earth.

TYPES OF ECOSYTEMS -- NATURAL AND HUMAN MODIFIED

Ecosystems are classified as natural or human modified depending upon whether they are fully

dependent on the solar radiation and on other natural sources of energy or on fertilizers and

fossil. A crop land in the village, an aquarium at home, or a park in the residential society are

maintained by human beings. These are some examples of human modified ecosystems. Natural

ecosystems are such as ponds, lakes, meadows, marshlands, grasslands, deserts and forests are

totally dependent on natural resources for their growth whereas, human modified ecosystems

depend on fertilizers, fossil fuel and other natural sources of energy manipulated by human

activities. Natural ecosystems

Natural ecosystems are of the following kinds

a. Ecosystem totally dependent on solar radiation e.g. forests, grass lands, oceans,

ponds, lakes, rivers and deserts. They provide food, fuel, fodder and medicine

to mankind.

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b. Ecosystems dependent on solar radiation and energy subsidies (additional

sources of energy) such as wind, rain and tides.Tropical rain forests, tidal

estuaries and coral reefs are the examples of these natural ecosystems.

Pond - An example of natural ecosystem

A pond is good example to understand the components, structure and functions of natural

ecosystems. It depends on solar radiation for energy and maintains its biotic community in

equilibrium with its abiotic components.

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Fig.12: Pond Ecosystem , showing biotic and abiotic components

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ABIOTIC COMPONENTS

1) Physical factors: Pond receives solar radiation, which provides it light and heat energy.

. (a) Light: In case of shallow ponds sun light can penetrate up to the bottom. In deep

ponds penetration of light depends on the transparency of water. The amount of

dissolved/suspended particles, nutrients and number of animals and plants determine

the transparency of water and control the penetration of light in it. On the basis of

penetration of light a pond it can be divided into euphotic, mesophotic and aphotic

zones. In upper part of the pond plenty of light is available to plants and animals is

called the euphotic zone. This zone is photosynthetically active and rate of

photosynthesis is more than respiration. The deeper layers of the pond where light

does not penetrate is known as aphotic zone. Photosynthesis can not take place due

to the absence of light therefore, autotrophs are completely absent and only

heterotrophs are found here. In the middle zone of the pond, designated as

mesophotic zone light intensity is reduced but it can support some autotrophs. This

middle zone where rate of photosynthesis is equal to rate of respiration is known as

zone of compensation. In this zone the amount of carbon dioxide produced by

respiration is completely used up in photosynthesis for the production of food.

(b) Temperature: Heating effect of solar radiation leads to diurnal (day and night) or

seasonal temperature cycles. In the tropical regions there are not much temperature

variations. At higher latitudes there are remarkable seasonal temperature variations.

Deep ponds and lakes show a seasonal thermal stratification. In the upper part of the

pond temperature changes are in accordance with the temperature of the surrounding

land and air.This upper zone of the pond is known as epilimnion. Middle zone shows a

rapid fall in temperature with the increasing depth (especially during summer months)

and is called thermocline”(metalimnion). Below the thermocline is hypolimnion in

which the temperature is more or less constant at 4o

C as water is heaviest at this

temperature.

2) Inorganic Substances: These are water, carbon, nitrogen, phosphorus, calcium and a

few other elements like sulphur or phosphorus depending on the location of the pond.

The other inorganic substances like O2 and CO2 are in the dissolved state in water.

Nitrogen, phosphorus, sulphur and other inorganic salts are held in reserve in bottom

sediment and inside the living organisms. A relatively small fraction of these salts is

present in the dissolved state in the pond.

3) Organic compounds: The commonly found organic matter in the pond is amino acids

and humic acids and the breakdown products of dead animals and plants. They are

partly dissolved in water and the remaining are accumulate in sediment. Decomposers

in the pond play an important role in determining the amount of organic matter.

BIOTIC COMPONENTS

The abiotic conditions of a pond and its geographical location determine its biotic

components. All the living organisms of the pond can be classified broadly into three main

groups namely, producers, consumers and decomposers

1) Producers or Autotrophs :. They synthesize food for all the heterotrophs of the pond.

They are of the following two types.

a) Floating plants

b) Rooted plants

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a) Floating plants: They are called phytoplankton (“phyto”- plants, “plankton” –

floating). They are small microscopic organisms which float in water and move in

the direction of water currents. Sometimes they are so abundant in pond that they

cover the entire surface and make it look green in colour e.g. Spirogyra, Ulothrix,

Cladophora, Volvox and diatoms.

b) Rooted plants: These plants occur in concentric layers from periphery to the

deeper zones. They can be distinguished into the following three zones:

i) Zone of emergent vegetation, e.g. Typha, bulrushes and Sagittaria..

ii) Zone of rooted vegetation with floating leaves, e.g. Nymphaea.

iii) Zone of submergent vegetation ,e.g. all pondweeds like Hydrilla, Rupia,

Chara and, musk grass etc.

2) Consumers/ Heterotrophs: Animals which feed directly or indirectly on autotrophs

e.g. insect larvae, tadpole, snails, sunfish and bass etc.

Pond animals can be classified into the following groups depending on their mode of

life

a) Zooplankton are floating animals many crustaceans like.(Cyclops,Cypris,Daphnia),

rotifers (Brachinus keratella). Like phytoplankton, zooplankton are also floating

organisms and are carried by water currents.

b) Nekton are the animals that can swim and navigate at will, e.g. fishes.

Benthic forms are the bottom dwellers like beetle, mites, molluscs and some crustaceans.

3) Decomposers: They are distributed in the whole pond but are most abundant at the

bottom of the pond in the sediment, e.g. bacteria and fungi (Rhizopus, Penicillium,

Curvularia, Cladosporium).

HUMAN MODIFIED ECOSYSTEMS

Human modified ecosystems are created by human beings for their own benefits. They may or

may not depend on solar energy. In agriculture and aquaculture solar energy is used along with

the nutrients provided by human beings whereas, urban and industrial ecosystems are

dependent on fossil fuel and other anthropogenic generated sources of energy.

Some of human modified ecosystems are like:

Agroecosystems, urban ecosystems, rural ecosystems, dams and reservoirs , aquaculture,

laboratory cultures and space ship etc.

Characteristics of human modified ecosystems

1) They are highly simplified.

2) Species diversity is very low.

3) They are highly unstable.

4) These ecosystems are partly or completely supported by anthropogenic inputs in the

form of energy, food and irrigation.

5) Food chains are simple and small.

6) Agroecosytems attract large number of weeds and pests.

7) They are more susceptible to diseases.

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8) Decomposers are relatively less in number.

9) They suffer from soil erosion

10) Human modified ecosystems need a lot of care for their sutainable productivity.

SOME EXAMPLES OF HUMAN MODIFIED ECOSYTEMS

Agroecosystems and Agricultural Practices

Agroecosystems are entirely human made ecosystems devoted primarily for the cultivation of

crops. Huge areas of forest and natural vegetation are cleared for large populations of

commercially important crop species. They are also known as crop ecosystems and are

mostly monoculture. Some times they are multi -species culture of field and garden crops. In

fact crop ecology is as old as human civilization.Intensive cultivation demands heavy soil

nutrients. To maintain their productivity large quantities of chemical fertilizers are added to

restore their nutrients whereas, in the natural ecosystems soil fertility is maintained without

adding any soil nutrients. Crops are irrigated therefore they have high demand of surface and

ground water.

Characteristics of Agroecosystem:

They are simple ecosystems and may be monoculture.

Species diversity is low.

Highly unstable ecosystems and are not self sustaining.

Attract large number of weeds and pests and get easily polluted.

Soil is poor in nutrient content as per their requirements, therefore they require

artificial nutrients or chemical fertilizers.

Productivity can be regulated by proper management through agricultural practices.

Agricultural practices: These include the proper management of the crop lands. Following are

the steps of agricultural practices:

1. Irrigation: using surface water of ponds, rivers and ground water from wells

2. Fertilizer application: addition of chemical fertilizers

3. Application of weedicides and pesticides: for control of weeds and pests

4. Ploughing Frequency: frequent ploughing of land is required.

5. Improved cropping system: by using modern biotechnological tools.

Disadvantages of agroecosystem:

• Wind erosion: Tiling causes large amount of wind erosion.

• Irrigation: Large quantities of water are required for irrigation.

• Pollutants: Agricultural practices can pollute the air with microorganisms like fungi,

algae, bacteria, viruses, pesticides, weedicides and increase soil salinity.

• Susceptibility to disease: Hybrid varieties are more susceptible to disease, e.g.

smut of sugarcane, maize and sorghum and rust of wheat and bajra are common in

crop plants and they are resistant to fungicides so the yield is affected.

• Loss of biodiversity: High yielding varieties are encouraged as a result of which the

naturally occurring varieties of crop are getting depleted.

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• Animal and plant diseases: Animals and humans consuming ergot infected bajra

suffer from ergot poisoning. It causes serious diseases of the nervous system.

Spore dust in heavily rust infected wheat field results in severe lung diseases.

Plantation Forests: Planting of selected species of trees over a piece of land resulting

into tree cover which resembles forest is called plantation forest. These are significantly

different from the natural forests as they are highly simplified and lack biodiversity. Fast

growing trees like neem, teak and shisham are generally planted.

Dams, Reservoirs and Diversions:

Dams, reservoirs and diversions capture and store run off water and release it as needed. A

dam is a structure built in order to restrict the flow of river or tidal water and provide fresh

water for following purposes :

• Producing hydroelectric power. This alternative source of energy reduces carbon

dioxide emission into the atmosphere.

• Supplying water for irrigation and other uses to rural, suburban and urban regions.

• Controlling floods.

• Reservoirs also provide recreational activities such as swimming and boating. Dams

have increased the annual run off available for human use nearly by one-third.

Disadvantages of dams:

• Dams cause permanent submergence of crop land and forests.

• Dams destroy farm lands and displace large number of local people.

• They increase water pollution because of reduced water flow. In the tropical

regions there is an increase the water born diseases. The local populations suffer

from water born diseases such as malaria, schistosomiasis and botulism ( a nervous

diseases resulting from blue green algae).

• Nutrients in the soil are reduced.

• The natural water flow regimes are disrupted, since it is a regulated flow of water the

spawning and migration of some fishes is affected.

• There is high cost of building the dams.

• Large dams which are more than 15 meters high (492 feet) increase earth quakes in

the seismically active areas.

• In arid region dams are resulting in increase in water salinity as the reservoirs (formed

by dams) have more exposed surface area and have a higher rate of evaporation than

the river.

• A dam has a limited life span usually 50 to 200 years. Because over the time the

reservoir fills with silt and it can not hold enough water to generate electricity.

AQUACULTURE:

Aquaculture is defined as the breeding, rearing and harvesting of plants and animals in all types

of aquatic environment including ponds, rivers, lakes, estuaries and oceans. It can take place in

the natural or in man made environment. It is a major source of global food supply. The marine

aquaculture deals with the production of oyster, clams, mussels, shrimps and salmon whereas,

freshwater aquaculture operations produce catfish, trout and tilapia and some more freshwater

32

fish and plants. Contribution of aquaculture to global food production depends on development

of present and future technology in mimicking the natural ecosystems. Aquaculture industry

should be able to recycle the nutrients and generate less waste like natural ecosystem.

From the economics point, aquaculture products can be grouped into two types: one high

valued species such as shrimps and salmon that are frequently grown for export. And second,

low valued species such as carp, tilapia, milk fish, clams and oyster. Carps accounts for more

than one- third of the world‟s aquaculture production. Carp farming is easy to integrate with

other conventional farm activities as well as they are herbivorous and can survive on low cost

readily available feed material. Tilapia is a good source of food but, they are among the

serious invasive species in subtropical and tropical regions. They are rapid breeders under

captivity, resistant to diseases but, fighters and affect the growth of other species of fish.

Tilapia is omnivorous and even digs soil to eat up detritus. Tilapia culture has been banned

in India since it is a prolific breeder and destroys the biodiversity of the ecosystem.

Aquaculture in India:

Marine: India has a very long coast line for tapping sea food. Marine resources include Bay of

Bengal, Arabian Sea, Indian ocean, numerous gulfs , coral reefs, mangroves and brackish

waters like lagoons and Chilka lake.

Fresh waters: India‟s inland waters occupy a very large area (about 1.6 million hectares).

They are in the form of major river systems such as Ganges, Yammuna, Brahmputra,

Narmada, Mahanadi, Cauvery and Krishna. Besides this there are wetlands, canals, ponds,

lakes, and irrigation channels where culture fishery can be practiced. The fresh water fishes

are various species of carps such as Chinese carp, green carp, mirror carps, cat fish etc.

The culture fisheries ( aquaculture) has been started in ponds, artificial enclosures and net pens

providing fertilizers such as cowdung, domestic waste and other animal excreta. The pond

cultures can be of the following types:

1. Monoculture: This involves production of only one species. Usually trouts, eels

and cat fish are produced in monoculture. .

2. Polyculture: The culture of more than one compatible aquatic species is called

polyculture. Common combinations are milk fish with prawn, Chinese carp with

Indian carp and carp with Tilapia.

Tilapia , trouts, salmon and some more species of fish are cultured in net pens. Milk fish and

mullets are cultured in enclosures or bamboo fences.

Environmental Impact of aquaculture

Aquaculture has many advantages. It provides improved qualities of fish with respect to

nutrients by crossing over and genetic engineering. It also reduces the over harvesting of

conventional fisheries. But both these profits are at the cost of environmental degradation.

• Aquaculture requires both land and waters resources, which are already in short supply.

• More man power is required for their maintenance.

• Large amount of concentrated wastes are produced.

• Coastal habitats with mangrove swamps are removed for the shrimp farming in Asia

and Africa . Destruction of Mangroves in coastal region has made them more prone to

cyclones, tornados and flooding. Thailand has lost 17% of its Mangrove forests.

• Aquaculture fish are very sensitive to pesticide runoff from the croplands

(biomagnification).

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• Dense populations are more vulnerable to diseases. Since the fish are reared under

highly controlled conditions they become more sensitive and prone to diseases.

URBAN ECOSYSTEM

An urban place is a city where many people live close together and the population density is

high. They consume a major part of the earth‟s resources and produce more waste. The earth

is witnessing urban revolution as the people all over the world crowd into towns and cities. In

1800 only 5% of the world population were urban dweller (50 million people) and in 1985 it

increased to 2 billion. At present 45% is urban population and by 2030 there will be more than

60% people living in cities.

Characteristics of urban ecosystem and their impact on the environment:

• Population density is high. There is too much of congestion (due to high population

density) that create inhumane conditions.

• It survives on major input of energy and natural resources.

• The economic growth of urban ecosystems is at the cost of environmental degradation.

• They are highly polluted since there are many industries releasing pollutants and very

few or no green plants to absorb them.

• Noise pollution is more severe due to more number of industry and noisy means of

transport.

• Urban ecosystems have water and other resource problem because of high population

density. They consume 75% of the earth‟s resource and produce 75% of the waste.

• There is more crime and unrest due to unemployment with population increase beyond

the carrying capacity. Increasing population density in the mega cities of the world

compels some people to live in slums (periphery of the city) e.g. 3 million people in

Mumbai live in slum and shanty town which lack basic services.

Urbanization is taking place more rapidly in the developing countries. The increase of city

dwellers in a developed (industrialized) country is only 0.8% whereas it is 3.6 % in the

developing country.

RURAL ECOSYSTEM

Rural ecosystems are between natural and urban ecosystems since, the exploitation of nature

and natural resources by man is relatively much less. People live here under comparatively

more natural conditions in simple life style.

Characteristics of Rural Ecosystem and their Impact on the Environment:

• In rural areas people live in small clusters surrounded by farm lands.

• In the villages people are mostly dependent on cultivation or farming.

• Clean water supply to them is in the form of wells, canals, lakes or rivers directly. These

sources may be quite far from the living place. Ladies and children spend a lot of their

time in fetching water and fire wood .

• Schools and modern sources of entertainments are beyond their reach.

• Transportation is poor.

• They are polluted by domestic sewage effluent and fossil fuel burning.

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• Poor sanitation and hygienic conditions.

• Houses are small and without ventilation.

The government policies to reduce the migration of people from villages to cities are to increase

the cost of land in the cities and reduce it in the villages. More employment should be created in

the villages. Some incentives should be given to the people working in the villages. More

facilities should be provided to the villagers so that they are not pushed towards the cities.

METHODS TO MINIMIZE HUMAN IMPACT ON NATURAL ECOSYSTEMS

Natural ecosystems are our resources especially for food, fuel and water. To protect them

from human impact it is essential to change our habits, curtail our needs and try to conserve

them for the future generations and to maintain the ecological balance in nature. This can be

done at the individual, community, national and global level.

Individual level: School and college students should take various initiatives to protect the

natural ecosystems. They should participate and organize seminars, camps and conferences

on various environment related issues. Their aim is to educate and inculcate environment

friendly attitude in people of all professions. People should be made aware of the consequences

of climate change and environmental degradation. They should be taught to economize the use

of energy and bioresources .

ƒ Plant trees in the neighbourhood and nurture them well.

ƒ Install energy efficient lightening system. Replace incandescent bulbs by compact

fluorescent bulbs. That last four times longer and use one- fourth of the electricity used

by the former.

ƒ Turn off all lights, fans, televisions air conditioners, computers and other electrical

gadgets when not in use.

ƒ Recycle all cans, bottles and plastic bags. Generate as little trash as possible. Trash in

landfills emits large quantities of methane and when incinerated releases carbon dioxide.

ƒ Use of electrical gadgets like washing machines, dish washing machine and iron should

be minimized.

ƒ Keep cars well tuned, get them serviced regularly. Try to pool cars. Use public transport

as far as possible.

ƒ Use cycle or walk for short distance shopping and visits.

Community level: At community level the concept to protect environment is very old in

India. It is observed in all the communities as most of them worship jal (water), vasu (air)

and prithvi (earth) on auspicious occasions.

i) Sacred groves in India are the ancient natural sanctuaries where all forms of life are

given natural protection by deity (saints or the tutelary who protect). These sacred

groves are still found in Himachal Pradesh, Maharashtra and Meghalaya.

ii) Bishnois of Rajasthan are Hindus that believe in protecting all kind of animals and

plants around them (especially khejri tree i.e. Prosopis cinera and black buck). They

do not even cut tree until it dies its natural death and only then they use it.

iii) Van Gujjars are indigenous forest dwellers living at the foot hills of Himalayas. They

live in full harmony with the natural ecosystem of forest. They lop off the branches of

the trees below the nodal points only at the time when the trees are shedding their leaves

so that the tree growth is not affected. Buffalo dung is used as a natural manure.

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iv) Chipko movement, name of the movement comes from a Hindi word meaning to

„embrace‟. The Mandal village women and local, Gram Swarajya Sangh (Dasoli)

headed by Mr. Chandi Prasad Bhatt to protect Aaknanda valley from deforestation.

They formed a human chain around the trees, hugged the trees and prevented them from

being felled in 1973. The success achieved by this act encouraged similar protest

movements in other parts of the country to protect forests and other natural ecosystems.

v) Narmada Bachao Andolan was initiated by Ms Medha Patkar to stop the construction

of dams on India‟s largest westward flowing river Narmada. In 1992 she was given

Goldman Environment Award for her dedicated effort to protect environment.

National level:

India is the seventh largest country of the world and second largest in Asia. It is the second

most populous country of the world with more than a billion people. India is the first country

to amend its constitution to give the state government the power to protect and improve their

environment. This 42nd

amendment was adopted in 1976 and came into effect in 1977. The

department of environment was created in 1980 and it became the Ministry of Environment and

Forests in 1985. There after various steps have been initiated for preservation, conservation and

mitigation.

The Energy and Research Institute (TERI), Headed by Dr. R.K. Pachauri is playing a vital

role in several environment related issues at students, community , national and international

level. Dr. R.K. Pachauri is also the chairman of IPPC and has been awarded Nobel prize in

2007.

India has one of the largest renewable energy program in the world and has made progress in

the field of wind, solar , geothermal and biomass energy. Use of solar cookers, solar heaters,

lanterns are encouraged . At Solar Energy Centre, Department of non- conventional sources

of energy, Gwalpahri several solar devices are being designed. In the rural areas (like Bakoli

village) many families are supplied with improved biogas stoves, biogas plants and other

cleaner sources of energy to reduce the emission of green house gases.

CNG (compressed natural gas) has replaced diesel and petroleum in many metro cities in public

and private transport vehicles.

For the conservation of natural biodiversity, the government along with NGOs and universities

has started establishing biodiversity restoration parks like Yammuna Biodiversity Park in

Jagatpur near Wazirabad, Aravalli Biodiversity Park,Vasant Vihar in Delhi and Asola Bhatti

Wild Life Sanctuary on the northern terminal of Aravalli hills near Gurgaon.

Asola- Batti wild life sanctuary is the only man made sanctuary which represents northern flat

topped hill form of country‟s oldest hill ranges – the Aravalli. This region is over exploited for

the extraction of quartzite, Badarpur or “bajri” by the mining communities.

Yammuna biodiversity park project is initiated by joint collaboration of Delhi Development

Authority and Centre for Environmental Management of Degraded Ecosystems in June 2002. It

is an excellent example of planners working in tandem and close association with scientists. In

the last four years it has shown a great progress in terms of improving the habitat for the growth

of 20 different communities. 51000 trees have been planted. Many species of migratory birds

which had reduced in number in India have started returning to this wetland.

Global level: Following conferences / and protocols are adopted at the international level to

protect our environment.

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1972: The Stockholm conference on Human Environment.

1988: The intergovernmental Panel on climate change (IPCC).

1990: IPCC released its first assessment report.

1922: UN framework convention on climate change (UNFCCC) was held at Rio de

Janeiro.154 countries participated in this convention.

1994: The convention entered into force.

1995, COP 1 (Conference of parties) held at Berlin Germany, IPCC finalized its second

assessment report.

1997, The Kyoto protocol was adopted at COP-3 in Japan.

2001, IPCC Finalized its third assessment report.

2005,UNFCCC, COP 11 \ MOP 1 (28 Nov. to 9 Dec.2005 ): Two meetings were held

simultaneously - the eleventh conference of the 189 parties to the 1992, UNFCCC on climate

change( COP 11) and the first meeting of 156 parties to the convention‟s 1997 Kyoto protocol

(MOP 1), which entered into force in February 2005. The important agenda was to make Kyoto

protocol fully operational by 2008 and decisions were taken to strengthen the functioning of

its innovative mechanisms. Another important issue was to develop global climate change

policies beyond 2012, when the Kyoto emission targets expire.

2006, UNFCCC: United Nations Environment Programme conference (16 Nov. 2006 ): was

held in Narobi to discuss the consequences of climate change on biodiversity and melting of

Glacial.

2007, UNFCC COP 13 (3-14 December): Conference was held at Bali , hosted by

Government of Indonesia.

India is a party to UNFCC and signed the multilateral treaty on June 10. 1992. Several

Ecoindustrial Revolution:

Ecoindustry or industrial ecology is to make industrial manufacturing processes more

sustainable by redesigning them to mimic how nature sustains them. The solution to many of

above problems is ecoindustrial revolution which will take place in another 50 years. It will

help to achieve industrial, economic and environmental sustainability. One way is by recycling

or reutilizing most of the chemicals.

• Industries interact in complex resource exchange web where the waste of one

manufacturer becomes the raw material for the other.

• Industry should be made far away from rural, urban or natural ecosystems .

SUMMARY

1. Ecosystem is a interacting unit of abiotic and biotic components of the biosphere.

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2. Climatic regime, inorganic substances, organic compounds, producers,

macroconsumers and microconsumers are the structural components of the

ecosystem

3. Functional processes of the ecosystem are food chains, energy flow, nutrient cycles,

ecological succession (ecosystem development) , and homeostasis.

4. All the abiotic factors such as light, temperature, pressure , humidity, salinity,

topography and the availability of various nutrients limit the growth and distribution

of animals and plants.

5. All the living organisms of an ecosystem are interdependent through food chains and

food webs. Removal of any single species of the community results in ecological

imbalance.

6. Source of energy for all the ecosystems is solar radiations which is absorbed by

autotrophs and passed on to the heterotophs in the form of food (organic substances).

Energy flow is always down hill and unidirectional.

7. Gross primary productivity (GPP) is the total amount of solar energy captured and

stored in the form of organic substances by the green plants. Net primary productivity

(NPP) is the amount of organic substances left in the plant after its own metabolism

i.e. GPP = NPP + plant respiration.

8. Trophic structure of the ecosystem can be represented graphically in the form of

ecological pyramids the base of the pyramid represents the producers and successive

tiers represent subsequent higher levels.

9. The nutrients move from the nonliving to the living and back to the nonliving

component of the ecosystem in a more or less circular manner. These nutrient cycles

are known as biogeochemical cycles.

10. The main components of all the biogeochemical cycles are:

a. the reservoir pool that contains the major bulk of the nutrients like soil or

atmosphere

b. cycling pool which are the living organisms (producers , consumers and

decomposers) , soil , water and air in which it stays temporarily for a short

period.

11. Human modified ecosystems are created by man for his own benefits. They may or

may not depend on solar energy and require fossil fuel or electrical energy generated

by human.

All man made ecosystems have some advantages to the human beings but many disadvantages

to the natural ecosystems and environment.

GLOSSARY

Community: It is an assemblage of species populations that occur together in the same place at

the same time. Its characteristics are determined by the interactions among the individuals

such as competition, predation, parasitism, energy flow and species diversity.

Food Chain: Transfer of food energy from the source in plants through a series of organisms

with repeated eating and being eaten is called food chain.

Food Web: In a community food chains are interconnected and interlocked to form a food web.

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Ecological pyramids: They are the graphical representations of number, biomass or energy

flowing through each trophic level in an ecosystem and are called pyramid of number, biomass

and energy respectively.

Ecological Efficiency: Ecological efficiency is defined as the percentage ratio of the energy

flow at different points along the food chain.

Reservoir pool: It is atmosphere or rock, where large stores of nutrient are present. These are

relatively long term stores of the nutrients.

Cycling pool: Plants and animals make the cycling pool. They are relatively short-term

stores.

Ecological Succession: A gradual progressive change in the species composition and

community structure over a period of time is called ecological succession. It can be autogenic

or allogenic. Autogenic succession is due to the changes resulting from the living organisms

themselves and allogenic succession is caused by environmental changes.

Phytoplankton: Small microscopic floating on the surface of water that moves with the water

currents is called phytoplanktons.

Zooplankton: These are small microscopic animals that float in water and move with the water

currents.

Euphotic Zone: Upper part of the pond, which receives sufficient quantity of light is called

euphotic zone in this part of the pond rate of photosynthesis, is more than respiration.

Aphotic Zone: This is that zone of the pond into which light does not penetrate .In dysphotic

zone rate of respiration is more than photosynthesis

Themocline: Zone of rapid temperature fall in a water body is called thermocline. This is also

known as metacline zone.

Homeostasis (Cybernetic):The capacity of an ecosystem to regulate its own functions such as

population size, species diversity and energy flow. It is known as cybernetic.

Resilience: Resilience is the speed with which a disturbed ecosystem returns to the state of

equilibrium after being disturbed by any external or internal factor.

Human Modified Ecosytems Human modified ecosystems are created by human beings for

their own benefits. They may or may not depend on solar energy. In agriculture and aquaculture

solar energy is used along with the nutrients provided by human beings whereas, urban and

industrial ecosystems are dependent on fossil fuel and other anthropogenic generated sources

of energy

Plantation Forests: Planting of selected species of trees over a piece of land resulting into

tree cover which resembles forest is called plantation forest. Fast growing trees like neem,

teak and shisham are generally planted.

Agroecosystems: Agroecosystems are entirely human made ecosystems devoted primarily for

the cultivation of crops. Huge areas of forest and natural vegetation are cleared for large

populations of commercially important crop species therefore they are also known as crop

ecosystems and are mostly monoculture.

Biodiversity restoration parks: These are made by humans to restore the threatened

ecosystems. For example many species of migratory birds have now stopped coming to India

as the wetlands are drying. Yammuna biodiversity park on the river bank has attracted these

species of birds because of the restoration of their habitat.

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UNFCC: United Nations Framework convention on climate change. It is an organization of

united nations working on the various environment related issues.

Suggested readings:

1. Elements of Eecology By Robert Leo Smith and Thomas M. Smith, Forth edition Pub:

Benjamin/Cumming publishing company Inc.

2. Ecology and Field Biology by Robert Leo Smith (Third edition), 1980 Pub: Harper

and Row , New York

3. Ecology by G.L. Clarke John, Pub: Wiley and Sons, Inc. ( NY,London, Sydney).

4. Fundamentals of Ecology by E.P.Odum Pub: W.B.Saunder‟s Company Ltd.

5. Environmental Science by William.P.Cunningham and Barbara Woodworth Saigo Pub:

Mc Graw Hills.

6. Comprehensive Environmental Studies by J.P.Sharma Pub: Laxmi Publications(P) Ltd.

7. Environmental Science , Towards A Sustainable Future,.Eighth Edtion, 2002, Richard

T. Wright and Bernard J Nebel. Pub: Prentice Hall of India Private Limited. New Delhi

- 110001.

8. Environmental Science by G.J.Miller Jr. Tenth edition, 2004, Pub: Thomson Brooks

/Cole.

9. Environment , International edition by Peter H. Raven, Linda R. Berg,andGeorge

B.Johnson.

10. Pub: Saunders College Publishing.

11. Ecology and Environment by P.D. Sharma, Pub :Rastogi Publications.

12. Essentials of Ecology and Environmental science by S.V.S. Rana Prentice- Hall of

India ,2005.