Unit .

Ecosystem 1

Definition and concept of Ecosystem

The interaction between living organisms and their environment is very much a two way process:
organisms affect and are in turn affected by their surroundings. Professor Arthur Tansley, a
British botanist, in 1935 proposed the term ecosystem and defined it as the "system resulting
from the integration of all living and non-living factors of the environment". He regarded
ecosystem as not only the organism complex but also the whole complex of physical factors
forming theenvironment.

Components of Ecosystem
The components of the ecosystem can be categorized into abiotic or non-living and biotic or
living components; Abiotic components: The important abiotic components are –
 Energy
 Material – a) Organic b)Inorganic
 ClimaticFactor
 EdaphicFactor

Biotic components - Biotic components include living organisms comprising plants, animals
and decomposers and are classified according to their functional attributes into producers and
consumers.
 Producers - Autotrophs (self-nourishing) are green plants as they synthesis
carbohydrates from simple inorganic raw materials like carbon dioxide and water in
the presence of sunlight by the process of photosynthesis for themselves, and
indirectly for othernon-producers.
 Consumers - Heterotrophs (other nourishing) are incapable of photosynthesis and
depend on organic food derived from animals, plants orboth.
i) Macro consumers or phagotrophs feed on plants or animals or both and are
categorised on the basis of their foodsources.
 Herbivores are primary consumers which feed mainly on plants e.g.
cow, rabbit. Carnivores feed only onanimals.
 Secondary consumers feed on primary consumers e.g.wolves.
 Carnivores which feed on secondary consumers are called tertiary
consumers e.g. lions which can eatwolves.
 Organisms which consume both plants and animals are called omnivores e.g.men.
ii) Micro consumers - Saprotrophs (decomposers) are chiefly bacteria and fungi
which obtain energy and nutrients by decomposing dead organic substances
(detritus) of plant and animal origin. Some of the products of decomposition

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 such as inorganic nutrients released in the ecosystem are reused by producers
and thus recycled. Earthworm and certain soil organisms such as nematodes,
and arthropods are also detritus feeders and help in the decomposition of
organicmatter.

Size of Ecosystem
Ecotone zone - The ecosystems often are separated, from adjacent ecosystems by a
transition zone or a diffused boundary zone called ecotone. Organisms of adjacent
ecosystems intermingle in the ecotone zone; consequently they may have greater
diversity of species than the neighbouring ecosystems.
Characteristics of Ecotone
 It may be very narrow or quitewide.
 It has the conditions intermediate to the adjacent ecosystems. Hence it is a zone oftension.
 It is linear as it shows progressive increase in species composition of one in
coming community and a simultaneous decrease in species of the other outgoing
adjoiningcommunity.
 Well-developed ecotones contain some organisms which are entirely different
from that of the adjoiningcommunities.
 Sometimes the number of species and the population density of some of the
species are much greater in this zone than either community. This is called
edgeeffect.
Types of Ecosystem

Natural and Artificial Ecosystem

i) Natural ecosystems are those which are mostly free from human disturbances, such as
tropical forests, grasslands, oceans, lakes anddeserts.

ii) Artificial or man-modified ecosystems are formed as a result of human modification of

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 the natural ecosystems. For example, man has transformed natural forests and
grasslands into crop fields. An extreme example of an artificial ecosystem is a city.
Increasing human interference hasdestroyed many natural ecosystems and replaced
them with artificial ecosystems, such as crop fields, urban centres and
industrialestates.
All ecosystems are fully integrated with the neighbouring ecosystems and communicate with
each other in varying degrees through the import and export of both energy and nutrients.
An ecosystem is a dynamic system characterized by energy flow and nutrients cycling.
Substances constantly flow through it, and there are sufficient supplies of energy within the
ecosystem to allow for this flow to take place.
Ecosystems also possess considerable self-regulating ability, called homeostasis, due to
which they tend to recover from minor perturbations.
Goods and Services provided by ecosystems include:
 Provision of food, fuel and fiber.
 Provision of shelter and buildingmaterials
 Purification of air and water
 Detoxification and decomposition ofwastes
 Stabilization and moderation of the Earth'sclimate
 Moderation of floods, droughts, temperature extremes and the forces ofwind.
 Generation and renewal of soil fertility, including nutrientcycling.
 Pollination of plants, including many crops Control of pests anddiseases
 Maintenance of genetic resources as key inputs to crop varieties and livestock breeds,
medicines, and other products
 Cultural and aesthetic benefits
Niche - A niche is the unique functional role or place of a species in an ecosystem. It is a
description of all the biological, physical and chemical factors that a species needs to survive,
stay healthy and reproduce.
A niche is unique for a species, which means no two species have exact identical niches.
Niche plays an important role in conservation of organisms. If we have to conserve species in its
native habitat we should have knowledge about the niche
requirements of the species and should ensure that all requirements of its niche are fulfilled.

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 Types of Niche
 Habitat niche - where itlives
 Food niche-what is eats or decomposes & what
species it competeswith
 Reproductive niche-how and when itreproduces.
 Physical & chemical niche - temperature, land
shape, land slope, humidity & otherrequirement.

Aquatic Zones
Aquatic systems are not called biomes; however they are divided into distinct life zones, with
regions of relatively distinct plant and animal life. The major differences between the various
aquatic zones are due to salinity, levels of dissolved nutrients; water temperature, depth of
sunlight penetration.

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 Biosphere
Biosphere is a part of the earth where life can exist. Biosphere represents a highly integrated and
interacting zone comprising of atmosphere (air), hydrosphere (water) and lithosphere(land).
It is a narrow layer around the surface of the earth. If we visualise the earth to be the size of an
apple the biosphere would be as thick as its skin.
Life in the biosphere is abundant between 200 m (660 feet) below the surface of the ocean and
about 6,000 m (20,000 feet) above sea level.
Biosphere is absent at extremes of the North and South poles, the highest mountains and
thedeepest oceans, since existing hostile conditions there do not support life. Occasionally spores
of fungi and bacteria do occur at great height beyond 8,000 m, but they are not metabolically
active, and hence represent only dormant life.
The energy required for the life within the biosphere comes from the sun. The nutrients
necessary for living organisms come from air, water and soil. The same chemicals are recycled
over and over again for life to continue.

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 Ecosystem function

Abiotic factor
Inorganic Substances: There are about forty elements that are required in various processes of
living organisms. Some of these are macronutrients which the plants need in relatively large
amounts, and others are micronutrients that are required in trace amounts. There are nine
macronutrients: carbon, hydrogen and oxygen (the three elements found in all organic
compounds), and nitrogen, potassium, calcium, phosphorus, magnesium, and Sulphur. Some
examples of micronutrients are: iron, chlorine, copper, manganese, zinc, molybdenum and boron.
Organic Substances: These include carbohydrates, proteins, lipids and their derivatives which
are derived from the waste products of plants and animals or are the remains of dead plants and
animals. Organic fragments of different sizes and composition formed as a result of
decomposition of organic residues are collectively called organic detritus. Decomposing organic
matter releases nutrients along with the formation of a dark, amorphous, colloidal substance
called humus which is important for the fertility of soil. New humus is added as old humus gets
converted into mineral elements.
Climatic Factors: This includes temperature, rainfall, humidity, and light, and their daily and
seasonal fluctuations. These abiotic constituents are very important for the survival and
continuation of living beings and the ecosystem.
Biotic Factor
Producers: Producers also called autotrophs are largely green plants that can make food from
simple inorganic materials. Food refers to complex organic compounds such as carbohydrates,
fats and proteins. Green plants accomplish food making through the process of photosynthesis.
In this process, green plants use carbon dioxide, water and some minerals, to produce
carbohydrates first and later various other-organic compounds such as fats and proteins. Oxygen
is given off by plants as a byproduct of photosynthesis. During photosynthesis, radiant energy of
sunlight is converted into chemical energy and is stored in the chemical bonds of the compounds
made by the plants.

 The major primary producers of aquatic ecosystems (freshwater and marine) are various species ofalgae.

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  In terrestrial ecosystems the major primary producers are predominantly herbaceous and woodyplants.
 Some photosynthetic prokaryotic organisms such as blue green algae and a few bacteria are
also called primary producers.
 Besides the green plants there are certain chemosynthetic bacteria that are also autotrophic.
But they obtain the energy for the synthesis of organic compounds (amino acids, proteins)
from sources other than solar energy. Some of these sources are: ammonia (NH3), methane
(CH4), and hydrogen sulphide(H2S).
Consumers: These are also called as phagotrophs or heterotrophs. The organisms grouped under
this category cannot manufacture their own food but obtain their energy and nutrients by feeding
on other organisms. Some eat primary producers (green plants) to get their food supply and are
called herbivores. In terrestrial ecosystem typical herbivores are insects, birds and mammals.
The animals which depend on herbivores for food are called secondary consumers. Since
secondary consumers feed on herbivores, they are therefore called carnivores. There are also
animals that feed on secondary consumers. They too are carnivores, and are known as tertiary
consumers. Secondary and tertiary consumers may be: a) predators which hunt, capture and kill
their prey; b) carrion feeders which feed on corpses; or c) parasites in which they are much
smaller than the host and they live on it while the host is alive. They depend on the metabolism
of their host for their energysupply.
There are some animals that have quite flexible food habits as they eat plants, (therefore are
herbivores) and animals (therefore are carnivores). They are known as omnivores of which man
himself is a good example
Decomposers: Also known as saprotrophs. Mostly, these are microscopic and are heterotrophic
in nature. Decomposer organisms obtain their energy and nutrients by degrading dead organic
matter. When plants and animals die, their bodies are still a source of energy and nutrients. These
organic remains are decomposed by micro- organisms, namely fungi and bacteria which grow
saprophytically on these remains. They secrete digestive enzymes from their bodies on the dead
and wasted materials, subsequently absorbing the products ofdigestion.
During the decomposition of wood, Fungi act and produce an enzyme cellulase, that softens the
wood. This enables the small animals to penetrate and ingest the material. Fragments of
decomposing material are called detritus, and many small animals feed on these, contributing to
the process of breakdown. They are called detritivores.
Because of the combined activities of the true decomposers (fungi and bacteria) and detritivores
(animals), in the breakdown (decomposition) of materials, they are sometimes collectively
referred to as decomposers. Although, strictly the term decomposer relates to saprophytic
organisms, some typical terrestrial detritivores are: earthworm, woodlice, millipedes and other
smaller (< 0.5 mm) animals such as mites, springtail and nematodes.

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 Trophic Level and Food Chain

TOLERANCE RANGE AND LIMITING FACTOR

Organisms are able to survive only within certain maximum and minimum limits with respect to
each environmental factor such as water, light and temperature. These are called the tolerance
limits and the range in between these limit is the tolerance ranges. Beyond the maximum and
minimum limits of this range no member of a particular species can survive.

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 Limiting Factor
In all ecosystems one factor, usually abiotic, limits the growth of organisms and is therefore
called a limiting factor. The limiting factor is one that outweighs all the other factors that are
necessary for the growth of organisms. It is the primary determinant for growth because it lies
beyond the minimum and maximum limits of the range of tolerance. For example, phosphorus is
a limiting factor in certain aquatic ecosystem. It is the first to be used up. When phosphorus is
reduced, the growth of algae is impaired. So, this is an example, where phosphorus is in short
supply and is thus a limiting factor. As mentioned above just as the shortage of any abiotic factor
impairs the survival of organisms in an ecosystem, so can an excess. Any factor that is in excess
may be detrimental for the living organisms, directly or indirectly.

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