A detailed description of the concept of ecosystem

1. Dr. Meenakshi Prasad
Assistant Professor
University Department of Geography
Magadh University, Bodh Gaya
AECC - 1

2. DISCLAIMER
The material for the presentation has been compiled from
various books and online sources & it is for general
information & educational purpose only. While the author
makes an endeavour to keep the information up to date
and correct she makes no representation of any kind
about the completeness and accuracy of the material.
The information shared through this presentation should be
used for educational purposes only.

3. CONTENT:
 Definition of Ecosystem
 Characteristics of Ecosystem
 Structure of Ecosystem
 Functions of Ecosystem
 Types of Ecosystem
 Ecosystem Services

4. DEFINITION
 The term ‘ecosystem’ was coined by A.G. Tansley, an English
botanist, in 1935.
 An ecosystem is the structural and functional unit of ecology
(nature) encompassing complex interaction between its biotic
(living) and abiotic (non-living) components.
 Forests, lake, pond, cropland, deserts are some of the common
examples of an ecosystem.

5.  Ecosystem was defined in its presently accepted form by
Eugene Odum as, “an unit that includes all the
organisms, i.e., the community in a given area
interacting with the physical environment so that a flow
of energy leads to clearly defined trophic structure,
biotic diversity and material cycles, i.e., exchange of
materials between living and non-living, within the
system”.

6. COMMON CHARACTERISTICS
Smith (1966) has summarized common characteristics of most of the
ecosystems as follows:
 The ecosystem is a major structural and functional unit of ecology.
 The structure of an ecosystem is related to its species diversity in the
sense that complex ecosystem have high species diversity.
 The function of ecosystem is related to energy flow and material
cycles within and outside the system.

7.  The relative amount of energy needed to maintain an
ecosystem depends on its structure. Complex ecosystems need
less energy to maintain themselves.
 Young ecosystems develop and change from less complex to
more complex ecosystems, through the process called
succession.
 Each ecosystem has its own energy budget, which cannot be
exceeded.
 Adaptation to local environmental conditions is the important
feature of the biotic components of an ecosystem, failing which
they might perish.

8.  The function of every ecosystem involves a series of
cycles, e.g., water cycle, nitrogen cycle, oxygen cycle,
etc. these cycles are driven by energy. A continuation or
existence of ecosystem demands exchange of
materials/nutrients to and from the different
components.

9. STRUTCURE OF AN ECOSYSTEM

10.  An ecosystem consists of two types of components –
(1)Abiotic and (2)Biotic
 Abiotic components - Abiotic components are the non-
living components of the ecosystem. The abiotic
component can be grouped into following categories:-
(a) Climatic Factors: Which include rain, temperature, light,
wind, humidity etc.
(b) Edaphic Factors: Which include soil, pH, topography
minerals etc.

11. Functions of Important Abiotic Components:
 Soil contains a mixture of weathered rock fragments, highly altered
soil mineral particles, organic matter and living organisms. Soils
provide nutrients, water, a home, and a structural growing medium
for organisms. The vegetation found growing on top of a soil is
closely linked to this component of an ecosystem through nutrient
cycling.
 The atmosphere provides organisms found within ecosystems with
carbon di-oxide for photosynthesis and oxygen for respiration. The
processes of evaporation, transpiration, condensation and
precipitation cycle water between the atmosphere and the Earth’s
surface

12.  Solar radiation is used in ecosystems to heat the atmosphere and to
evaporate and transpire water into the atmosphere. Sunlight is also
necessary for photosynthesis. Photosynthesis provides the energy for plant
growth and metabolism, and the organic food for other forms of life.
 Most living tissue is composed of a very high percentage of water, up to
and even exceeding 90%. The protoplasm of a very few cells can survive if
their water content drops below 10%, and most are killed if it is less than
30-50%. Water is the medium by which mineral nutrients enter and are
trans-located in plants. It is also necessary for the maintenance of leaf
turgidity and is required for photosynthetic chemical reactions. Plants and
animals receive their water from the Earth’s surface and soil. The original
source of this water is precipitation from the atmosphere.

13.  Biotic Components - The living organisms including plants, animals and
micro-organisms (Bacteria and Fungi) that are present in an
ecosystem form the biotic components.
 (A) Producers: Producers are organisms which are able to
manufacture their own food. The green plants have chlorophyll with
the help of which they trap solar energy and change it into chemical
energy of carbohydrates using simple inorganic compounds namely
water and carbon dioxide. This process is known as photosynthesis. As
the green plants manufacture their own food they are known as
producers . Producers are also known as autotrophs (i.e. auto = self,
trophos = feeder). The chemical energy stored by the producers is
utilised partly by the producers for their own growth and survival and
the remaining is stored in the plant parts for their future use.

14.  (B) Consumers: Consumers are organisms which are unable to
synthesise their own food. Therefore, they depend on the producers
for their food. They are also known as heterotrophs (i.e. heteros =
other, trophos = feeder)
The consumers are of four types, namely:
 (a) Primary Consumers or First Order Consumers or Herbivores: These
are the animals which feed on plants or the producers. They are
called herbivores. Examples are rabbit, deer, goat, cattle etc.

15.  (b) Secondary Consumers or Second Order Consumers or Primary
Carnivores: The animals which feed on the herbivores are called
the primary carnivores. Examples are cats, foxes, snakes etc.
 (c) Tertiary Consumers or Third Order Consumers: These are the
large carnivores which feed on the secondary consumers.
Example are Wolves.
 (d) Quaternary Consumers or Fourth Order Consumers or
Omnivores: These are the largest carnivores which feed on the
tertiary consumers. Examples are bear, man

16.  (C) Decomposers or Reducers: Bacteria and fungi belong to this
category. They breakdown the dead organic materials of
producers (plants) and consumers (animals) for their food and
re-lease to the environment the simple inorganic and organic
substances produced as by-products of their metabolisms. These
simple substances are reused by the producers resulting in a
cyclic ex-change of materials between the biotic community
and the abiotic environment of the ecosystem. The
decomposers are known as Saprotrophs (i.e., sapros = rotten,
trophos = feeder).

18. FUNCTIONS OF ECOSYSTEM
 (i) Productivity
 (ii) Decomposition
 (iii) Physical (energy flow)
 (iv) Biological (food chains, food web, ecological
succession),and
 (v) Biogeochemical (nutrient cycling) processes

19. (i)Productivity
 The rate of biomass production in an ecosystem is called its
productivity.
 The total weight or amount of living matter in per unit area is
known as biomass and it is expressed as dry weight.
 Productivity is generally expressed in terms of g/m2/year or kcal
/m2/year .
 Productivity in ecosystems is of two kinds, primary and
secondary.

20. Primary Productivity:
 Primary production is defined as the amount of biomass or organic
matter produced per unit area over a time period by plants during
photosynthesis. In other words primary productivity refers to the rate
at which sunlight is captured by producers for the synthesis of
energy-rich organic compounds through photosynthesis.
 Primary productivity has two aspects, gross and net.
 The rate of total capture of energy or the rate of total production of
organic material (biomass) is known as gross primary productivity
(GPP). Gross primary productivity of an ecosystem is the rate of
production of organic matter during photosynthesis.

21.  A considerable amount of GPP is utilised by plants in respiration.
The balance energy or biomass remaining after meeting the cost
of respiration of producers is called net primary productivity (NPP).
Net Primary productivity = Gross Primary productivity – respiration loss
 Net primary productivity is the available biomass for the
consumption to heterotrophs.
 There is a positive correlation between solar radiation and primary
productivity. It also depends upon the availability of nutrients,
availability of moisture in the soil and the photosynthetic capacity
of plant species present within an ecosystem.

22.  Except a few exception the primary productivity decreases as we
move from the equator towards the poles (as insolation decreases as
we move from the equator towards the poles). It also decreases from
the coastal sea waters towards the deep sea.
 In aquatic ecosystems productivity is generally limited by light,
which decreases exponentially with increasing water depth. In
deep oceans,7 nutrients often become limiting for productivity.
Nitrogen is regarded as the most important nutrient limiting
productivity in marine ecosystems.
 The annual net primary productivity of the whole biosphere is
approximately 170 billion tons (dry weight) of organic matter. Of this,
despite occupying about 70 per cent of the surface, the productivity of
the oceans are only 55 billion tons.

24. Secondary Productivity:
 Secondary productivity is defined as the rate of formation of
new organic matter by consumers.

25. (ii) Decomposition
 Decomposition is the process of breaking down of complex
organic matter into inorganic substances like carbon dioxide,
water and nutrients by the decomposers.
 The upper layer of soil is the main site for decomposition processes
in the ecosystem.
 Dead plant parts and animal remains constitute detritus, which is
the raw material for decomposition.

26. Factors affecting Decomposition:
 Decomposition is largely an oxygen requiring process.
 The rate of decomposition is controlled by chemical composition of
detritus and climatic factors.
 In a particular climatic condition, decomposition rate is slower if detritus is
rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-
soluble substances like sugars.
 Temperature and soil moisture are the most important climatic factors that
regulate decomposition through their effects on the activities of soil
microbes. Warm and moist environment favour decomposition whereas
low temperature and anaerobiosis inhibit decomposition resulting in build
up of organic materials.

27. Decomposition Processes:
(a) Fragmentation
(b)Leaching
(c) Catabolism
(d) Humification
(e) Mineralisation

28. (a) Fragmentation : Fragmentation is the process of breaking
down of detritus into smaller particles by detrivores (detritus
feeding invertebrates e.g., earthworm). The detritus gets
pulverized when passing through the digestive tracts of animals.
Due to fragmentation the surface area of detritus particles is
greatly increased.
(b) Leaching : In the process of leaching watersoluble substances
(eg – sugars) from the fragmented detritus go down into the soil
horizon with the percolating water and get precipitated as
unavailable salts.

29. (c) Catabolism : The extracellular enzymes released by bacteria
and fungi carry out catabolism i.e. enzymatic conversion of the
decomposing detritus to simpler compounds and inorganic
substances.
(d) Humification : Humification leads to accumulation of a dark
coloured amorphous substance called humus. Humus is highly
resistant to microbial action and undergoes extremely slow
decomposition. It serves as a reservoir of nutrients.
(e) Mineralisation - The humus is further degraded by some
microbes and release of inorganic nutrients (e.g. CO2, H2O) and
available nutrients (NH4 +, Ca++, Mg++, K+ etc.) in the soil. occur
by the process known as mineralisation.

30.  Under certain conditions, soil nutrients get tied up with the biomass of
microbes and become temporarily unavailable to other organisms. Such
incorporation of nutrients in living microbes is called nutrient
immobilization. Nutrients remain immobilized for variable periods and get
mineralized later after the death of microbes. This immobilization prevents
the nutrients from being washed out from the ecosystem.
 It is important to know that all the three decomposition processes, i.e.
fragmentation, leaching and catabolism operate simultaneously on the
detritus. Humification and mineralization occur during decomposition in
the soil
 With the passage of time, decomposing detritus loses weight until it
disappears completely. If decomposition is retarded or stopped, large
amounts of partially decomposed organic matter shall accumulate in the
ecosystem.

31. (iii)Energy Flow
 Energy flow is the key function in the ecosystem. The storage and
expenditure of energy in the ecosystem is based on two basic laws of
thermodynamics.
 First law of thermodynamics, that states that energy can neither be
created nor destroyed, it can only change from one form to another. In
accordance with the first law of thermodynamics , energy of sunlight can
be transformed into energy of food and heat.
 Second law of thermodynamics, that states that as energy is transferred
more and more of it is wasted. Thus, in ecosystem, the transfer of food
energy from one organism to another leads to degradation and loss of a
major fraction of food energy as heat due to metabolic activities, with
only a small fraction being stored in living tissues or biomass.

32.  The energy flow in the ecosystem is one of the major factors that
support the survival of organisms.
 For almost all organisms on earth, the primary source of energy is solar
energy. We receive less than 50 per cent of the sun’s effective
radiation on earth. When we say effective radiation, we mean the
radiation which can be used by plants to carry out photosynthesis.
 This effective radiation is termed as the Photosynthetically Active
Radiation (PAR) and only around 2-10 percent of it is used by plants
for the process of photosynthesis. Thus, this percent of PAR supports
the entire world as plants are the producers in the ecosystem and all
the other organisms are either directly or indirectly dependent on
them for their survival.

33.  The energy flow takes place via food chain and food web. During the
process of energy flow in the ecosystem, plants being the producers
absorb sunlight with the help of the chloroplasts and a part of it is
transformed into chemical energy in the process of photosynthesis.
 This energy is stored in various organic products in the plants and
passed on to the primary consumers in the food chain when the
herbivores consume (primary consumers) the plants as food and
convert chemical energy accumulated in plant products into kinetic
energy, degradation of energy will occur through its conversion into
heat.
 They are followed by the secondary consumers. When these
herbivores are consumed by carnivores of the first order (secondary
consumers) further degradation will occur. Finally, when tertiary
consumers consume the carnivores, again energy will be degraded.
Thus, the energy flow is unidirectional in nature.

34.  Based on the source of their nutrition or food, organisms
occupy a specific place in the food chain that is known as
their trophic level. Producers belong to the first trophic level,
herbivores (primary consumer) to the second and carnivores
(secondary consumer) to the third.
 The amount of energy decreases at successive trophic levels.
Organisms at each trophic level depend on those at the lower
trophic level for their energy demands. Each trophic level has
a certain mass of living material at a particular time called as
the standing crop. The standing crop is measured as the mass
of living organisms (biomass) or the number in a unit area. The
biomass of a species is expressed in terms of fresh or dry
weight.

35.  In a food chain, the energy
flow follows the 10 percent law.
According to this law, only 10
percent of energy is transferred
from one trophic level to the
other; rest is lost into the
atmosphere.
 The ten percent law of transfer
of energy from one trophic
level to the next can be
attributed to Raymond
Lindeman (1942), although
Lindeman did not call it a "law"
and cited ecological
efficiencies ranging from 0.1%
to 37.5%.

36. (iv)Biological Functions:
(A) Food Chain - The transfer
of food energy from the
producers, through a series of
organisms (herbivores to
carnivores to decomposers)
with repeated eating and
being eaten, is known as food
chain. In nature, basically two
types of food chains are
recognized – (a)grazing food
chain and (b)detritus food
chain.
Source: google images

37. (a) Grazing Food Chain - Grazing food chain extends from
producers through herbivores to carnivores. Cattle grazing in
grasslands, deer browsing in forest and insects feeding on
crops and trees are most common biotic constituents of the
grazing food chain.
(b) Detritus Food Chain - Detritus food chain begins with dead
organic matter and passes through detritus-feeding organisms
in soil to organisms feeding on detritus-feeders. A much larger
fraction of energy flows through the detritus food chain.

38. (B) Food Web - Simple food
chains are very rare in nature
because each organism may
obtain food from more than
one trophic level. Thus, in an
ecosystem, the various food
chains are interconnected to
each other to form a network
called food web.
Source – google images

40. (C) Ecological Succession:
 An important characteristic of all communities is that their
composition and structure constantly change in response to
the changing environmental conditions.
 This change is orderly and sequential, parallel with the changes
in the physical environment. These changes lead finally to a
community that is in near equilibrium with the environment and
that is called a climax community.
 The gradual and fairly predictable change in the species
composition of a given area is called ecological succession.

41.  During succession, changes occur both in plant and animal
communities. The changes in plant community are,
however, more marked and visible.
Source : google images
ECOLOGICAL SUCCESSION

42.  Ecological Succession can be of two types – (a)Primary Succession &
(b)Secondary Succession.
 (a)Primary Succession - When the succession takes place on new sites
(previously unoccupied by organisms), it is called primary succession.
Examples of primary succession sites are: bare rocks, glacial moraines
(formed after glaciers have moved away), volcanic lava deposits etc.
Such sites, which are invaded by organisms for the first time, are limited
in area.
 (b)Secondary Succession - Much larger surface of earth is covered
with plants, but the existing plant cover is often partially or completely
destroyed due to some disturbance caused by events like fire,
landslide, forest felling etc. In such situations after the cessation of
disturbance the plant cover gradually develops again through the
process called secondary succession. Expectedly secondary
succession occurs over much larger area than primary succession.

43. MODEL OF ECOOGICAL SUCCESSION
Source: google images

44.  During succession some species colonise an area and their populations
become more numerous, whereas populations of other species decline
and even disappear.
SOME IMPORTANT TERMS:
 Pioneer Species - Whenever succession begins on bare land or in a
previously occupied habitat, the plant species colonizing in the
beginning are called pioneer species. Commonly the pioneer plant
species are small in size (e.g. herbs), short-lived (e.g. annuals), and
rapidly growing. Pioneer species have to grow in relatively harsh
habitat conditions where adequate supply of water and nutrients may
not be assured. Hence, such species have evolved life history strategy
to complete growth and reproduction within short time when optimum
environmental conditions are available in the habitat.

45.  Pioneer Community - The initial community developing
through the assemblage of the pioneer species is called
pioneer community. With the passage of time, the pioneer
community shows change in species composition due to
disappearance of pioneer species and colonization of new
species. Thus, the pioneer community is replaced by second
community, then second community is replaced by the third,
and the process goes on.
 Sere - The sequence of communities succeeding each other
during the course of succession represents the sere.

46.  Seral Community & Seral Stage - The successive communities
at a site are called seral communities, with each community
representing a seral stage.
 Early Successional Species & Late Successional Species - The
species coming in early during succession are known as early
successional species, and those making appearance much
later are called late successional species. By the time the late
successional species get established the community
becomes complex, being comprised of a large number of
species showing intricate mutual interactions.

47.  Climax Community – The terminal community of succession
reached in an ecosystem is known as the climax community.
Compared to preceding communities, the climax community is
stable. The species composition of the climax community
remains unchanged as long as the environmental conditions
remain unaltered and no disturbance sets in. The time required
to attain climax stage varies widely with the nature of
community; for instance, grassland community may reach
climax stage within few years or decades, but forest succession
may require several decades, sometimes more than a century,
to attain climax stage.

48. Succession in Plants:
 Based on the nature of the habitat – whether it is water (or very
wet areas) or it is on very dry areas – succession of plants is called
hydrarch or xerarch, respectively.
 (b)Xerarch Succession - Succession occurring on land deficient
in moisture is called xerarch succession. In xerarch succession,
generally lower plants like lichens and mosses are pioneer
species, which are followed by invasion of herbaceous plants,
and finally the climax community is established. The climax in
xerarch succession may be represented by a20 grassland
community in lower rainfall conditions. In higher rainfall
conditions the xerarch succession may lead to the formation of a
forest community.

49.  (a) Hydrarch Succession - When succession proceeds in
aquatic conditions (e.g. pond, lake), it is known as hydrarch
succession. The hydrarch succession in standing water begins
with the pioneer community formed by phytoplankton and
zooplankton. As a result of silting in the water body due to soil
erosion from surrounding areas, the pond bottom is raised
causing replacement of the pioneer community by rooted
plants with leaves floating or emerged over water surface. With
the continuance of silting and accumulation of decomposing
plant residues the water body gradually gets filled up, making
way for the establishment of terrestrial plants like grasses. Thus,
hydrarch succession may lead to the disappearance of the
water body which is converted into terrestrial conditions.

50. (V)Biogeochemical Processes (Nutrient Cycle):
 The living organisms require several chemical elements for their life
processes. Plants can photosynthesize simple compounds like
carbohydrates using carbon, hydrogen and oxygen obtained from
carbon dioxide and water; however, for the synthesis of more
complex materials (e.g. proteins) they requires supply of additional
essential elements or nutrients.
 Some nutrients are required in large amounts (e.g. nitrogen and
phosphorus) but others are needed in trace amounts (e.g. zinc,
molybdenum, copper etc.)
 Nutrients may be used as part of the structural components or as
components of enzymes which mediate various life processes.

51.  Unlike energy which flows unidirectionally, nutrients are
continually exchanged between organisms and their physical
environment. Nutrient cycles involve storage and transfer of
nutrients through various components of the ecosystem so that
the nutrients are repeatedly used. Another term
biogeochemical cycle (bio = living organisms and geo = rocks,
air and water) also denotes nutrient cycling. But
biogeochemical cycle is generally considered in a regional or
global context.
 Nutrient cycles are of two types, the gaseous and the
sedimentary.

52.  The reservoir for gaseous type of nutrient cycle (e.g., nitrogen,
carbon cycle) exists in the atmosphere and for the sedimentary
cycle (e.g., sulphur and phosphorus cycle), the reservoir is
located in Earth’s crust.
 Nutrient cycles can be conveniently considered under the
following three aspects:
(i)Input of nutrients
(ii)Output of nutrients &
(iii)Internal nutrient cycling

54. (i)Input of Nutrients - Ecosystem receives nutrients from external
sources and stores them for further use through biological
processes. For example, nutrients in dissolved state are gained
from rainfall (wet deposition) or in particulate state from dust fall
(dry deposition). Symbiotic biological fixation of nitrogen in soil
also represents an input. Weathering of soil parent materials
which releases available nutrients from their fixed state is
another example of input.

55. (ii) Output of Nutrients -Nutrients are moved out of an ecosystem
and many become input to another ecosystem. For example,
considerable loss of nutrients like calcium and magnesium
occurs through runoff water or through soil erosion. Significant
amount of nitrogen may be lost in gaseous form by the
denitrification process in soil. Harvesting of agricultural crops or
transportation of logs from forests represent nutrient loss from
these ecosystems.

56. (iii) Internal Nutrient Cycle - Plants absorb varying amounts of
nutrients from the soil. Due to decomposition of dead organic
matter nutrients are continuously regenerated and stored in soil in
forms available to the plant. A dynamic state exists in soil with
nutrient regeneration and absorption occurring simultaneously.
The transfer of nutrients from the soil to plants by the process of
nutrient absorption is known as uptake. The absorbed nutrients are
metabolically incorporated in plants during growth. Periodically
nutrients are recycled, i.e. brought back to soil through litter fall
from vegetation, animal remains and faecal matter, etc.. The
aboveground as well as root detritus decompose to regenerate
the nutrients. Eventually nutrients contained in the detritus on soil
surface and within, are regenerated by decomposition in plant-
available forms.

57.  When the uptake of nutrients exceeds the amount recycled
(e.g. as in the case of a young growing forest), a fraction of the
uptake is retained in the standing crop.
 This retention of balance nutrients in the standing crop leads to
increase in nutrient content of the ecosystem. Thus, in a nutrient
cycle:
Retention = Uptake – Recycle
 Rates of nutrient uptake, recycle and retention vary widely in
different ecosystems.

58.  In an undisturbed ecosystem (i.e. an ecosystem in which human
activities are absent or nearly so) the input of nutrients may
approximately equal the output of nutrients, rendering the nutrient
cycles more or less balanced.
 Generally the absolute amounts of nutrient moving in (input) and
moving out (output) of the ecosystem are much less than the
amount of nutrients cycled within (amongst different components)
the ecosystem.
 Severe disturbances in the ecosystem (e.g. tree felling, insect out
break, fire, soil erosion, etc.) may make the nutrient cycles
unbalanced and the ecosystem unstable. To exemplify, after
removal of natural vegetation the soil can be lost rapidly by erosion.

59. TYPES OF ECOSYSTEM
 Ecosystems are broadly classified into two categories:
(1)terrestrial & (2) aquatic. Terrestrial ecosystems are
land-based, while aquatic are water-based. The word
“biome” may also be used to describe terrestrial
ecosystems which extend across a large geographic
area, such as tundra.

60. Terrestrial Ecosystem:
 The ecosystem which is found only on landforms is known as the
terrestrial ecosystem. The main factor which differentiates the
terrestrial ecosystems from the aquatic ecosystems is the relative
shortage of water in the terrestrial ecosystems and as a result the
importance that water attains in these ecosystems due to its
limited availability. Another factor is the better availability of light
in these ecosystems as the environment is a lot cleaner in land
than it is in water. The main types of terrestrial ecosystems are
(a) the forest ecosystems
(b) the desert ecosystems
(c) the grassland ecosystems and
(d) the tundra ecosystems.

61. (a) Forest Ecosystem :
 These ecosystems have an abundance of flora or plants and hence
in these ecosystems a large number of organisms live in a small
space. This means that these ecosystems have a high density of
living organisms.
 These ecosystems are classified according to their climate type as
tropical, temperate or boreal i.e; tropical evergreen forest, tropical
deciduous forest, temperate evergreen forest, temperate deciduous
forest and taiga.
 In the tropics, rainforest ecosystems contain more diverse flora and
fauna than ecosystems in any other region on earth. In these warm,
moisture-laden environments, trees grow tall and foliage is lush and
dense, with species inhabiting the forest floor all the way up to the
canopy.

62.  In temperate zones, forest ecosystems may be deciduous,
coniferous or often times a mixture of both, in which some
trees shed their leaves each fall, while others remain
evergreen year-round.
 In the far north, just south of the Arctic, boreal forests – also
known as taiga – feature abundant coniferous trees.

63. (b) Grassland Ecosystem :
 The grasslands are the areas which comprise mainly of the
grass with a little number of shrubs and trees.
 Grazing animals, insectivores and herbivores are the main
types of organisms which are found in these regions.
 Grasslands share the common climactic characteristic of semi-
aridity. Trees are sparse or non-existent, but flowers may be
interspersed with the grasses. Grasslands provide an ideal
environment for grazing animals.

64.  There are two types of grasslands – (i)Tropical & (ii)Temperate
 Tropical grasslands have tall and coarse grass. They are known
as savanna in Africa and Llanos and campos in South America.
 Temperate grasslands have short and soft grass. They are
known steppes in Eurasia, praries in North America, Pampas in
South America, Veld in Africa and Downs in Australia.

65. (c) Desert Ecosystem :
 The common defining feature among desert ecosystems is low
precipitation, generally less than 25 centimeters, or 10 inches, per
year.
 Almost 17% of all the land on this planet is occupied by the desert
ecosystems.
 The fauna and flora in these ecosystems is generally not much
developed because of the high temperatures, intense sunlight and
low availability of water. The main vegetation of such regions are the
shrubs, bushes and a few grasses and trees.

66.  The stems and leaves of these plants are also developed in
order to conserve as much water as possible (xerophytic
plants).
 Camels, reptiles and some insects and birds are the living
creatures which are found in such regions.
 Not all deserts are hot – desert ecosystems can exist from the
tropics to the arctic, but regardless of latitude, deserts are often
windy. Some deserts contain sand dunes, while others feature
mostly rock.

67. (d) Tundra Ecosystem :
 As with deserts, a harsh environment characterizes ecosystems in the
tundra. In the snow covered, windswept, treeless tundra, the soil may
be frozen year-round, a condition known as permafrost.
 Another important feature about these ecosystems is that the
animals which live here have thick fur coats for protection against
cold and generally have a long hibernation period in the winters.
 During the brief spring and summer, snows melt, producing shallow
ponds which attract migrating waterfowl. Lichens and small flowers
may become visible during this time of year.

68. (2) Aquatic Ecosystem :
 An ecosystem which exists in a body of water is known as an
aquatic ecosystem. The communities of living organisms
which are dependent on each other and the aquatic
surroundings of their environment for their survival exist in the
aquatic ecosystems.
 The aquatic ecosystems are mainly of two types, (A)the
freshwater ecosystems and (B) the marine ecosystems.

69. (A) Marine Ecosystem:
 Marine ecosystems are the biggest ecosystems. They cover
around 71% of earth’s surface and also contain almost around
97% of the total water present on earth.
 Marine ecosystems differ from freshwater ecosystems in that
they contain saltwater, which usually supports different types
of species than does freshwater.
 Marine ecosystems are the most abundant types of
ecosystems in the word. They encompass not only the ocean
floor and surface but also tidal zones, estuaries, salt marshes
and saltwater swamps, mangroves and coral reefs.

70.  The marine ecosystem can further
be divided into 3 categories –
(a)Neritic – the shallow water area
near the coast (on the continental
shelf)
(b)Pelagic – the open sea
ecosystem
(c)Benthic – the deep sea
ecosystem
Pelagic Zone
Source : google images

71. (B) Fresh Water Ecosystem :
 The freshwater ecosystems are very small in magnitude as
compared to the marine ecosystems as these covers only 0.8% of
the earth’s surface and only account for 0.009% of the total water
present on earth.
 There are three basic kinds of freshwater ecosystems and these are
Lentic, Lotic, and Wetlands.
 The lentic ecosystems are slow-moving or still (standing) water
ecosystems like ponds or lakes.
 Lotic ecosystems are ecosystems with moving water, for example –
river.

72.  The wetlands are those systems where soil remains
saturated for a long period of time. Many different species
of reptiles, amphibians, and around 41% of the world’s fish
species live in these ecosystems.
 The faster moving waters contain more dissolved oxygen
than the slow moving waters and hence support greater
biodiversity. Also the temperature of water is slightly higher
in a still water ecosystem as compared to a moving water
ecosystem.

73. ECOSYSTEM SERVICES:
 Ecosystem services are the benefits that people obtain from ecosystems.
They support, directly or indirectly, our survival and quality of life.
 Some ecosystem services are well known, such as those which are essential
for life (e.g. food and clean air and water) or those which improve our
quality of life (e.g. recreation and beautiful landscapes). Other services are
often taken for granted, such as natural processes (e.g. pollination and flood
regulation)
 According to the Millennium Ecosystem Assessment (MA) that 60% of
ecosystem services are being degraded or used unsustainably, often
resulting in significant harm to human well-being.

74.  The MA (Millennium Ecosystem Assessment) categorised
ecosystem services into four classes:
(1) Provisioning Services
(2) Regulating Services
(3) Cultural Services
(4) Supporting Services

75. (1) Provisioning Services :
 It includes the products obtained from ecosystems, such as
food, water, fuel and materials for building.
 Agro-ecosystems provide food for human consumption and,
together with the associated ecosystems supporting marine
and freshwater fisheries, underpin global food security.
 Ecosystems play important roles in the global hydrological
cycle, contributing to water provision, regulation and
purification (Dudley and Stolton 2003; Bruijnzeel 2004; Brauman
et al. 2007).

76.  The provision of fuels and fibres, medicinal and other
biochemical resources such as metabolites, pharmaceuticals,
nutrients, crop protection chemicals, cosmetics and other
natural products for industrial use and as a basis for
biomimetics that may become increasingly important in
nanotechnology applications is also made by ecosystem.
(Ninan 2009).
 Biodiversity has also played an iconic, ornamental role
throughout the development of human society. Uses of plant
and animal parts, especially plumage of birds, have been
important in conferring individual status, position and
influence. Ornamental plants are typically grown for the
display of their flowers but other common ornamental
features include leaves, scent, fruit, stem and bark are also
widely used.

77. (2) Regulating Services:
 , Ecosystems contribute to several of natural processes, like air
quality regulation, climate regulation, water/flood regulation,
disease and pest control, pollination and water purification,
environmental regulation services of importance for human
wellbeing, particularly in urban areas where vegetation reduce air
and noise pollution, mitigate the “urban heat island effect”
(Santomouris, 2001), and reduce impacts related to climate
change (Bolund and Hunhammar, 1999).
 Vegetation cover also play a key factor in preventing soil erosion
and vegetation cover combined with drought resulted in
unprecedented wind erosion, destroying farmland and livelihoods.

78. (3) Cultural Services:
 Cultural services are the non-material benefits people, obtain
from ecosystems and landscapes through spiritual
enrichment, recreation and aesthetic enjoyment.
(4) Supporting Services:
 Supporting services include services such as soil formation,
photosynthesis and nutrient and water cycling which are
necessary for the production of all other ecosystem services.

79.  In some estimates, over 75% of the world's crop plants, as well
as many plants that are source species for pharmaceutical s ,
rely on pollination by animal vectors (Nabhan and Buchman,
1997).
 Klein et al. (2007) found that, for 87 out of 115 leading global
crops (representing up to 35% of the global food supply), fruit
or seed numbers or quality were increased through animal
pollination.
 In many agricultural systems, pollination is actively managed
through the establishment of populations of domesticated
pollinators, particularly the honeybee.

80. SUGGESTED READINGS:
 https://www.nationalgeographic.org/encyclopedia/ecosystem/#:~
:text=Powered%20by,An%20ecosystem%20is%20a%20geographic%2
0area%20where%20plants%2C%20animals%2C%20and,abiotic%20fa
ctors%2C%20or%20nonliving%20parts.
 https://globalchange.umich.edu/globalchange1/current/lectures/k
ling/ecosystem/ecosystem.html
 https://www.yourarticlelibrary.com/environment/ecosystem/ecosyst
ems-concept-types-and-basic-structure-of-an-ecosystem/30110
 https://www.ugc.ac.in/oldpdf/modelcurriculum/Chapter3.pdf
 http://eagri.org/eagri50/ENVS302/pdf/lec04.pdf
 https://www.deshbandhucollege.ac.in/pdf/resources/1587401626_B
A(H)-Psc-Eco-Eng-BA(P)-II-Ecosystem.pdf