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Ecosystem Part-2



❖ Besides some lower plants such as lichens & xerophytic mosses are also present.

2) Consumer Organisms

These include animals such as insects, reptiles which are capable of living in xeric conditions

❖ Besides some nocturnal rodents, birds & some mammalians like camel etc are also found.

3) Decomposers

Due to poor vegetation with very low amount of dead organic matter, decomposers are poor in
desert ecosystem.

❖ The common decomposers are some bacteria & fungi, most of which are thermophillic.

II. Abiotic components

Due to high temperature & very low rainfall, the organic substances are poorly present in the soil.

Fig. 2.5 Forest Ecosystem


1. Introduction

❖ Aquatic ecosystems deal with biotic community present in water bodies.

❖ In terrestrial ecosystem, carbon dioxide & oxygen are present in gaseous form whereas in
aquatic ecosystem, these are available in dissolved state.



❖ Depending upon the quality and nature of water, the aquatic ecosystem are categorized into:

❖ Freshwater Ecosystem and

❖ Marine Ecosystem.

2. Freshwater Ecosystems

❖ Freshwater ecosystems cover 0.8% of the Earth’s surface and contain 0.009% of its total

❖ Freshwater ecosystems contain 41% of the world’s known fish species.

❖ Aquatic ecosystems perform many important environmental functions. For example:

➢ They recycle nutrients, purify water, attenuate floods, recharge ground water and
provide habitats for wildlife.

➢ Aquatic ecosystems are also used for human recreation, and are very important to
the tourism industry, especially in coastal region.

❖ There are three basic types of freshwater ecosystems:

❑ Lentic: slow-moving water, including Pools, Ponds, and Lakes.

❑ Lotic: rapidly-moving water, for example Streams and Rivers.

❑ Wetlands: areas where the soil is saturated with water or inundated for at least
part of the time

3. Lakes & pond Ecosystem

❖ A pond is a place where living organisms not only live but interact with biotic & abiotic

❖ Ponds are often exposed to tremendous anthropogenic pressure which significantly affects the

❖ Lakes are usually big standing freshwater bodies.

❖ They have a shallow water zone called Littoral zone; an open water zone where effective
penetration of solar light takes place, called limnetic zone and a deep water zone where light
penetration is negligible, called Profoundal zone.

I. Biotic components

1) Producer Organisms

❖ It includes submerged, free floating and amphibious macrophytes (like; Hydrilla, Utricularia,
Wolfia, Azolla, Typha etc.) and minute floating and suspended lower phytoplanktons (like;
Ulothrix, Spirogyra, Oedogonium etc.)

2) Consumer Organisms

a)Primary consumers:These are zooplanktons (ciliates, flagellates, other protozoan, small
crustaceans) and benthos.

b) Secondary consumers: These are carnivores like insects and fishes feeding on herbivores

c) Tertiary consumers: These are the large fishes feeding on small fishes.

3) Decomposers Micro – organisms like bacteria, fungi and actinomyctes.

II. Abiotic component



❖ These are the inorganic as well as organic substances present in the bottom soil or dissolved
in water. In addition, to the minerals, some dead organic matter is also present.

Fig.2.6.4 Zonation in a lake ecosystem

4. Marine or Ocean Ecosystem

❖ Marine ecosystems are among the Earth’s aquatic ecosystems. They include: Oceans,
Estuaries and Lagoons, Mangroves and Coral reefs, the Deep sea and the Sea floor.

❖ These are the gigantic reservoirs of water covering approximately 71% of
the Earth’s surface (an area of some 361 million square kilometers).

❖ These ecosystems are different from freshwater ecosystem mainly because of its salty water.

❖ The salt concentration in an open sea is usually 3.5% (35 parts per thousand (ppt)). Dominant
ions are sodium & chloride.

❖ Average temperature of Marine ecosystem is 2-3 degree centigrade, devoid of light.

I. Biotic components

1)Producers It includes phytoplanktons (diatoms, dinoflagillates), large seaweeds (mainly algae like
chlorophyceae, phaeophyceae & rhodophyceae; angiosperms like Ruppia, Zostera, posidonia ), and
mangrove vegetation (like Rhizophora, Carapa etc.)

2) Consumers

a)Primary consumers: These are herbivores and feed directly on producers (Crustaceans, Mollusks,
fish etc.)

b) Secondary consumers: These are carnivorous fishes (Herring, Sahd and Mackerel)

c) Tertiary consumers: These are top carnivorous fishes (Cod, Haddock, etc.)

3) Decomposers These are micro – organisms like bacteria, fungi

II. Abiotic components

❖ High Na, Ca, Mg and K salt concentration, variable dissolved oxygen content, light &
temperature make a unique physiochemical conditions in marine water.



Fig.2.6.5 Ocean Ecosystem


❖ All organisms must obtain a supply of energy and nutrients from their environment in order to

❖ The transformations of energy in an ecosystem begin first with the input of energy from the

❖ Because, it is the first step in the production of energy for living things, it is called “Primary

❖ Photosynthesis — Chemical reaction where green plants use water & carbon dioxide to store
the sun’s energy in glucose.

❖ ENERGY is stored in glucose.

❖ Glucose is stored as starch in plants

❖ The majority of autotrophs are photoautotrophs that harness the energy of the sun and pass
some of this energy onto consumers through feeding pathways.

❖ The energy contained within producers and consumers is ultimately passed to the
decomposers that are responsible for the constant recycling of nutrients.

❖ Thus, there is a one-way flow of energy through the biotic community and a cycling of
nutrients between the biotic and abiotic components of the ecosystem

❖ Energy flow cannot occur in reverse direction.

❖ Starts from autotrophs (the producer level, i.e., first trophic level) to Heterotrophs including
plant eaters or Herbivores (second trophic level) and so on.

❖ The amount of energy decreases with successive trophic levels.

❖ Only About 1% of energy from the sun is used by green plants & rest remains unutilized.

❖ Similarly, there is loss of energy in each trophic level.

❖ The transfer of food energy between the organisms in an ecosystem can be tracked by
constructing food chains, food webs, pyramids of numbers, biomass and energy and energy
flow diagrams.



Fig.2.7 Energy Flow


❖ A food chain may be defined as, “the transfer of energy and nutrients through a series of
organisms with repeated process of eating and being eaten”.

❖ In an ecosystem, all the organisms are linked together with one another by food relationship.

❖ Each organism living or dead is potential food for some other organism.



Fig.2.8 Food Chain


❖ Under natural conditions, the linear arrangement of food chains hardly occurs & these
remains connected interconnected with each other through different types of organisms.

❖ Interlocking pattern of several interlinked food chains is termed as FOOD WEB.



Fig.2.9 Food web in grassland ecosystem


❖ An”Ecological pyramid” is a graphical representation that shows the relative amounts of
energy or matter contained within each tropic level in a food chain or food web.

❖ An ecological pyramid shows the relationship between consumers and producers at different
tropic levels in an ecosystem

❖ There are three ecological pyramids recognized by ecologists:

1. Pyramid of Numbers

✓ Shows the relative number of individual organisms at each tropic level.

2.10.2 Pyramid of Biomass



❖ A pyramid of biomass represents the total dry mass (in grams per square meter of area) of all
the organisms in each tropic level at a particular time.

3. Pyramid of Energy

❖ A pyramid of biomass represents the rate of energy flow and/or productivity at successive
tropic levels. The pyramids of energy are always upright.


❖ Nutrient cycles involve storage and transfer of nutrients through different components of the
ecosystem, so that the nutrients are repeadly used.

❖ The cyclic movements of chemical elements of the biosphere between the organisms and
environment are referred as “BIOGEOCHEMICALCYCLES”

Gaseous cycle: Those elements in which the reservoir is the air or the oceans (via evaporation).
Gaseous cycles include those of Carbon, Nitrogen, Oxygen, Carbon, and Water.

Sedimentary cycle: Those elements which are received from the Earth’s crust. Sedimentary cycles
include those of iron, calcium, phosphorus, and other more earth bound elements.


❖ Nitrogen is crucial for all organisms

❖ Nucleic acids



❖ Proteins

❖ Chlorophyll

❖ Nitrogen- 78% in Atmosphere

❖ N2 is very stable and must be broken apart by organisms, combined with other atoms into a
usable form.

❖ Nitogen cycle completes in 5 steps:

1) Nitrogen Fixation

Conversion of N2 → NH3

❖ Combustion, volcanic action, Lightning, Industrial processes (making fertilizer). Bacteria
(Azotobactor, Clostridium, Nostoc etc.)

2) Nitrification

Conversion of NH3 → NO3

Soil bacteria convert in a two step process.

3) Assimilation

Roots absorb NH3, NH4, or NO3 and incorporate them into nucleic acids and protein.

4) Ammonification

Amino acids and nucleotides are broken down into waste products NH3 or NH4

5) Denitrification

The reduction of NO3 to N2 .Denitrifying bacteria return some of the nitrogen to the



Wet & dry
Atmospheric Nitrogen deposition

Nitrogen fixation by free
living & symbiotic Denitrification

microbes. Pseudomonas

Consumers Plants

Detritus Litter fall



Soil ammonia Nitrosomonas Soil nitrite Soil nitrate

Fig.2.11.1 Nitrogen Cycle


❖ Carbon enters plants, etc., as CO2

▪ Bacteria process carbon in a fashion that allows it to be recycled.

▪ Obtain energy from the molecules, and convert carbohydrates to carbon dioxide as a
result of respiration.

❖ Photosynthesis removes carbon from the abiotic environment (fixes carbon into organic

❖ Carbon moves through food chain through consumption of one organisms by another

❖ Cellular respiration, combustion, and erosion of limestone return carbon to the atmosphere,
water and abiotic environment.









Fig.2.11.2 Carbon Cycle

The source of atmospheric carbon dioxide is variable but only plants can utilize atmospheric
carbon directly


❖ The only cycle that does not have a gaseous state

❖ Inorganic phosphate PO 3-
4 is released from rocks and sediments through the action of


❖ Soil PO 3-
4 is absorbed by plants and incorporated into nucleic acids, phospholipids and ATP.

❖ Animals obtain most of their PO –

4 by consumption of other animals and from water.

❖ PO 3-
4 is released to the soil again by decomposers.

• Dissolved PO 3-
4 gets absorbed by algae and aquatic plants

• Decomposers break down waste and returns PO 3-
4 to sediments on the seabed.

• Some returns to terrestrial environment through geologic processes and via seabirds. Guano



Parental Rock

Soluble PO 3-

4 in soil. Insoluble phosphate

Plants (Roots)

Animals Death

Bone/ Teeth



Fig.2.11.3 Phosphorus Cycle


❖ Ecological succession is defined as, “A change in the community in which new populations of
organisms gradually replace existing ones”.

❖ There are two types of ecological succession:

1) Primary Succession

❖ Occurs where there is no soil, e.g. after a volcanic eruption or a glacial retreat.

❖ “Pioneer organisms”

❖ Simple plants first – no or shallow roots.

❖ Gradual influx of more complicated and larger plants as the habitat changes

❖ Unfavorable for life at first.

❖ Ends with a “climax community” – ecosystem stays constant, provided there are no changes
in abiotic influences.

2) Secondary Succession

❖ Community development in the areas that were previously occupied by a other community.

❖ Occurs after a disturbance. E.g., loss of trees after disease, Fire or wind, deforestation etc.

❖ Conditions are favorable for as soil and nutrients are already present.

❖ More rapid than primary succession.



Primary Succession Vs Secondary Succession

Primary Secondary

➢ No soil. ➢ Soil already exists.

➢ Pioneer species. ➢ Seeds have suitable soil conditions.

➢ Weathering & decomposition ➢ Occurs much faster.

➢ Humus and sand increase over time. ➢ Climax community.

➢ End = Climax community.


❖ Biodiversity is the variety and differences among living organisms from all sources, including
terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they
are a part.

❖ It is virtually synonymous with “Life on earth”.

❖ Biologists most often define “biological diversity” or “biodiversity” as the “totality of genes,
species, and ecosystems of a region”.

❖ The biodiversity found on Earth today consists of many millions of distinct biological species,
which is the product of nearly 3.5 billion years of evolution.

2.13.1 Levels of Biodiversity

1) Genetic diversity

❖ It is a level of biodiversity that refers to the total number of genetic characteristics in the
genetic makeup of a species.

❖ It is distinguished from genetic variability, which describes the tendency of genetic
characteristics to vary.

2) Species diversity

❖ It refers to the variety of species within a region.

❖ Species diversity is an index that incorporates the number of species in an area and also their
relative abundance.

❖ It is generally a much more useful value than species richness.

3) Community and Ecosystem diversity

❖ Ecosystem diversity refers to the diversity of a place at the level of ecosystems. This has 3

❖ Alpha Diversity: Within community diversity. Alpha diversity refers to the diversity of
organisms sharing the same Community/Habitat.

❖ Beta Diversity: Between community diversity. It refers to the diversity of organisms sharing
two habitats.

❖ Gamma Diversity: Diversity of the habitat over the total landscape or geographical area is
called gamma diversity.



2. Values of Biodiversity

Food: About 80,000 edible plants and about 90% of present day food crops have been
domesticated from wild.

Drugs & Medicines: About 75% of world’s population depends on plants or plant extracts.

Fuel: Forests have been used since ages for fuel wood. Fossil fuels are also products of

Social Value: Many of the plants like Tulsi, Lotus, Peepal etc are considered holy and sacred.

❖ About 2.1 million species have been identified till date, while many more species are believed
to exist.

❖ According to UNEP estimate, approximately 9.0 – 52 million of species exist on Earth

❖ India’s position is 10th in the world & 4th in Asia in terms of Plant diversity.


❖ A biodiversity hotspot is a biogeographic region with a significant reservoir
of biodiversity that is threatened with destruction.

❖ An area is designated as a hot spot when it contains at least 0.5% of plant species as endemic.

❖ There are 25 such hot spots of biodiversity on a global level, out of which two are present in

❖ These are: Indo- Burma (earlier The Eastern Himalayas) ,The western Ghats & Sri Lanka..

❖ These hot spots covering less than 2% of the world’s land area are found to have about 50%
of the terrestrial biodiversity.

2.14.1 Criteria for determining hot-spots

❖ No. of Endemic Species i.e. the species which are found no where else.

❖ Degree of threat, which is measured in terms of Habitat loss.

E.g. Indo- Burma (Eastern Himalayas) Hotspot

❖ The hotspot includes all of Cambodia, Vietnam & Laos, and nearly the entire areas of
Thailand, Myanmar & Bhutan as well as part of Nepal, far eastern India and extreme southern

❖ In addition, it covers several offshore Islands including Mainan Islands in the south China Sea
and Andaman & Nicobar Islands in Indian Ocean.

❖ Indo-Burma is one of the most threatened biodiversity hotspots, due to the rate of resource
exploitation and habitat loss.

E.g. Western Ghats and Sri Lanka

❖ Western Ghats and Sri Lanka, also known as the “Sahyadri Hills” encompasses the montane
forests in the southwestern parts of India and on the neighboring Islands of Sri Lanka.

❖ The entire extent of hotspot was originally about 1,82,500 square kms, but due to tremendous
population pressure, now only 12,445 square Km or 6.8% is in pristine condition.

❖ The important populations include Asian elephant, Indian tigers and the endangered lion
tailed macaque.




❖ Extinction is a natural event and, from a geological perspective, routine.

❖ In last century, human impact has been so severe that thousands of species and varieties are
becoming extinct annually.

❖ Some of the main causes are:

❖ Habitat loss, degradation, fragmentation.

❖ Habitat loss & degradation are major causes of species extinction, affecting 89% of all
threatened birds, 83% of mammals & 91% of all threatened plants assessed globally (IUCN,

❖ The main causes of habitat are agriculture activities, Mining, development of human
settlement, industry etc.

❖ According to ICUN, UNEP report, more than 50% of wildlife habitat has been destroyed in
49 out of 61 old world tropical countries.


❖ Poaching is another threat that has emerged in recent decades as one of the primary reason for
decline in number of species.

❖ Wildlife is sold and traded in many countries for live specimens, folk medicines, furs, Skin,
and other products such as Ivory, horns etc amounting to millions of dollars.


❖ The conflict between man and wildlife started with the evolution of man, but intensity
increased due to the activities of modern man

❖ Due to the lack of stable food and disruption of movement, wild animals came out of forest
area and attack the agricultural field and humans and in turn got killed by the humans.

2.17.1 Introduction of Exotic species

❖ Organisms introduced into habitats where they are not native are termed as exotics.

❖ They can be thought of as Biological Pollutants and are considered to be among the most
damaging agents of habitat alteration and degradation the world.

2.17.2 Climate change
A changing global climate threatens species and ecosystems.

❖ The distribution of species (biogeography) is largely determined by climate.

❖ Climate change may simply shift these distributions but, for a number of reasons, plants and
animals may not be able to adjust.


❖ According to The International Union of Conservation of Nature and Natural Resources
(IUCN), the species that considered in imminent danger of extinction and whose survival is
unlikely, if factors causing their decline continue to operate.

❖ Out of about 47,000 species of plants in our country, 7000 are endemic

❖ India contains 172 species of animals considered globally threatened by IUCN, or 2.9% of the
world’s total number of threatened species.

❖ These include 53 species of mammals, 69 birds, 23 reptiles and 3 amphibians



❖ As many as 3,000- 4,000 higher plants may be under high degree of threat in India

❖ Thus Indian subcontinent has about 62% endemic flora, restricted mainly to Himalayas, khasi
Hills & Western Ghats.

❖ Sapria himalayana, Uvaria lurida, Napenthes khasians etc. are some endemic flora of our

❖ A large number out of a total of 81,000 species of animals in our country is endemic. About
62% amphibians and 50% lizards are endemic to western Ghats.

❖ Golden monkey, Niligiri Langur, Indian Wolf, Red Fox, Himalayan Brown Bear, Great
Indian One Horned Rhinoceros, White Winged Wood Duck, Black Necked Crane, Indian Pea
Fowl, Gharial, Indian egg eating Snake, Indian Salamandar etc. are some examples of
endemic animal species of India.


❖ The convention on Biological Diversity held in June, 1992 stressed the need of the
conservation of Biodiversity for sustainable development and perpetuation of human beings
on earth.

❖ Conservation is defined as “ the management of human use of the biosphere so that it may
yield the greatest sustainable benefit to the present generation while maintaining its potential
to meet the needs and aspirations of the future generations”.

❖ The two basic approaches to wildlife conservation in protected habitats are:

1) In- situ conservation 2) Ex- situ conservation.

1. In- situ conservation

❖ It simply means conservation of species in its natural ecosystem or even in man made

❖ This strategy emphasizes protection of total ecosystem through a network of “protected area”.

❖ Protected Areas: an area of land and/or sea specially dedicated to the protection and
maintenance of biological diversity and managed through legal effective means.

❖ There are different categories of protected areas which are managed with different objectives.
These include; Biosphere reserves, National parks, Wild Life Sanctuaries etc.

❖ At present we have 11 major biosphere reserves, 80 National parks, 420 wildlife sanctuaries
in our country covering 4% of the geographic area.

❖ The JIM CORBETT National Park was 1st national park established in India.

What is Difference among Biosphere reserves, National parks, Wild Life Sanctuaries ?

Examples of Biosphere reserves of India:

1. Nilgiri- 5,520

2. Nanda Devi- 5,860.69 sq. km

3. Manas – 2837 sq. km

4. Gulf of Mannar – 10,500 sq. km

5. Great Nicobar – 885 sq. km

6. Panchmarhi – 4,926.28 Sq Km



Examples of some National park in India

1. Kaziranga- Assam, Gir National Park- Gujarat, Periyar – Kerala, Sariska – Rajasthan

Examples of some Wild Life Sanctuaries of India:

1. Ghana Bird sanctuaries

2. Hazaribagh sanctuaries

3. Abohar wild life sanctuaries

4. Jaldapara wild life sanctuaries

5. Mudamalai wild life sanctuaries

2. Ex- situ conservation

❖ It is defined as “the conservation of component of biological diversity (Sample of genetic
diversity, particularly of endangered species) outside their natural habitats”.

❖ It involves maintenance and breeding of endangered plant and animal species under partially
or wholly controlled conditions. E.g. Zoos, Botanical Gardens, Aquaria, Nurseries, DNA
bank, Seed bank, Gene bank etc.

❖ There are more than 1500 Botanical gardens in the world containing more than 80,000

❖ There are more than 800 zoos around the world with about 3,000 species of mammals, birds,
reptiles and amphibians.

Review questions:

1. Define Environmental science.
Environmental science is the study of the environment, its biotic and abiotic components and
their interrelationships.

2. What are the important components of environment?
Abiotic or non-living components Biotic or living component Energy component

3. What are the processes involved in hydrological cycle?
Continuous evaporation, transpiration, precipitation of surface run off and ground water

4. Define biogeochemical cycle. Give example.
The continuous circulation of all the essential elements and compounds required for life, from
the environment to the organism and back to the environment.e.g., carbon cycle.

5. What are the functions of lithosphere? It is a home for human beings and wild

lives. It is a store house minerals and organic matters

6. Mention the various types of public participation.
▪ Pressure group ▪ Watch dog
▪ Advisory council ▪ Enforcing the environmental laws

7. Explain biosphere?

The part of lithosphere, hydrosphere and atmosphere in which living organisms live and
interact with one another is called biosphere.