COURSE NAME: ENVIRONMENTAL STUDIES FOR
UNDERGRADUATES FOR ALL COURSES
PAPER TITLE: ENVIRONMENTAL STUDIES FOR
UNDERGRADUATES
UNIT: 3 - ECOSYSTEM
TOPIC: CONCEPT OF AN ECOSYSTEM
OBJECTIVE: At the end of this program we would be able to answer the following
questions:1. We study the concept of an ecosystem to know more about natures’
intricate balance systems.
2. It helps us to identify the different components that are interdependent in
an ecosystem.
3. It also provides an insight into the different aspects of an ecosystem like:
i) definition,
ii) components,
iii) relationships,
iv) classification,
v) characteristics,
vi) extent and regions,
vii) energy considerations etc
4. It also makes us aware of the different types of ecosystems in the world
and that artificial or man made ecosystems have their own position in the
study of ecosystems.
1. Introduction
Nature is bountiful. It has been providing and replenishing resources from
time immemorial. It has a rhythm in chaos, a balance in disorder, life in
nonliving.
Man has been ever instrumental in making manipulations in his or her
surroundings to suit his/her needs thereby creating alterations in nature
which disrupt certain balances in it. Man forms an integral part of the
environment with all its living and nonliving components and their intricate
interrelationships. Understanding and recognising the importance of the
intricate balance of nature is necessary for man’s own existence.
Eugene Odum, a founder of ecology, stated: "Any unit that includes all of the
organisms (ie: 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 nonliving parts) within the system is an ecosystem. The
term ecosystem was coined in 1935 by British ecologist Arthur G.Tansley
who also refined the term, describing it as the interactive system established
between biocoenosis -a group of living creatures, and their biotope -the
environment in which they live. (A debate does exist regarding who had first
coined the term ‘Ecosystem’)*
Ecosystem definition: An ecosystem is a natural system consisting of all
plants, animals and microorganisms (biotic factors) in an area functioning
together with all the non-living physical (abiotic) factors of the environment
(Christopherson 1997).
There are no conceptual restrictions on how large or small a space or an
area must be to host an ecosystem, nor on the minimum number of species
or individual organisms to be present.
Early conceptions of an ecosystem were as a structured functional unit in
equilibrium of energy and that matter flows among constituent elements.
Some considered this vision limited, and preferred to view an ecosystem in
terms of cybernetics, as applied specifically to collections of organisms and
relevant abiotic components.
According to the Convention on Biological Diversity, (CBD), signed by almost
200 nations: "Ecosystem" means a dynamic complex of plant, animal and
micro-organism communities and their non-living environment interacting as
a functional unit" (Convention on the Biological Diversity, 1992).
An ecosystem can exist in any place where there are varied forms of life.A
small freshwater pond or a small lake is the classic example of an
ecosystem.
Components of an Ecosystem
Ecosystem can be basically divided into two components:
1: Biotic Components
2: Abiotic Components
Biotic componentsThe living organisms including micro-organisms(like bacteria and fungi),
plants and animals that are present in an ecosystem form the biotic
components. Based on the role in the ecosystem the biotic components can
be classified into three types. These are:
1. Producers (autotrophs)
2. Consumers (heterotrophs)
3. Decomposers (saprotrophs, detrivores)
Producers- Also called the autotrophs (Auto=self,troph=feeder) are
organisms that are capable of making their food themselves. Green plants,
grasses, mosses etc are autotrophic components. Producers have green
pigment called chlorophyll traps the energy of sunlight to convert carbon
dioxide and water into carbohydrates by releasing oxygen into the
atmosphere (by the process of respiration carbon dioxide is released into the
atmosphere).The chemical energy stored by the producers is partly used by
them for their growth and survival while the remaining is stored for use at
other trophic levels (primary consumer, secondary consumer etc)
Consumers – Also called as heterotrophs (hetero=other,troph=feeder)are
directly or indirectly dependent on autotrophs for their energy / food
requirements. Depending on their food habits consumers are divided asi) Herbivores-Also called as primary producers, these are consumers
that eat plants for their energy and nutrients. These may be insects,
zooplankton or other animals. Example-bee, deer, goat.
ii) Carnivores- Also called as secondary consumers, feed on herbivores and
may also consume other carnivores. Example- fox, wolf, tiger, shark
iii) Omnivore-Those organisms which eat both plants and animals are
omnivores.
Example- man, hen
3. Decomposers or reducers or saprotrophs-These are heterotrophic
organisms breakdown the complex compounds into simple products which
are utilized by producers or by decomposers themselves.These are called as
microconsumers as well.Example- Bacteria and fungi.
Abiotic Components- The non-living things in the ecosystem that are
involved in the material cycles are collectively called as abiotic
components.These enter the body of living organisms, take part in metabolic
activities and then return to the environment.
These may be divided asi) Climatic factors-Solar radiation, temperature, wind, water current,
rainfall etc.
ii) Physical factors-Light, fire, pressure etc.
iii) Chemical factors-Acidity, salinity, inorganic nutrients, gases, minerals
etc.
The abiotic factors exhibit diurnal, nocturnal, seasonal and annual changes.
These have a strong influence on the structure, distribution, behavior and
interrelationships of organisms in an ecosystem.
Characteristics of an Ecosystem
Some of the characteristics of ecosystem are –
i) Ecosystem is the major ecological unit.
ii) It contains both biotic and abiotic components.
iii) The boundary of an ecosystem is not rigidly defined and it is flexible.
iv) Through the biotic and abiotic components nutrient cycle and energy
flow occur.
v) The function of ecosystem is related to the cycling of materials and
flow of energy.
vi) The amount of energy needed to maintain an ecosystem depends on
its structure.
vii)Ecosystems pass from a less complex state to more complex state,
which is called as succession.
viii) Adaptation to local environmental condition is the important feature
of the biotic components of an ecosystem, failing which they might
perish.
Classification of Ecosystem:
Ecosystem may generally be classified into three types
1. Natural Ecosystem
2. Artificial Ecosystem
3. Incomplete Ecosystem
1. Natural Ecosystem- A natural ecosystem is developed and governed
by nature. These are capable of operating and maintaining themselves
without any major interference by man. The following are the two types of
natural ecosystem based on their habitat.
Terrestrial- forests, grasslands and deserts
Aquatic- freshwater, marine and estuarine
2. Artificial Ecosystem-An artificial ecosystem is created and maintained
by man for his different needs. Some of the artificial ecosystems are
reservoirs, artificial lakes, croplands, townships and cities.
3. Incomplete Ecosystems- An ecosystem which does not contain all the
four basic components( Abiotic substances, Producers, Consumers and
Decomposers) are known as incomplete ecosystems. Some incomplete
ecosystems are - abysmal depths in the sea/ocean and caves which lack
producers but contain abiotic substances, consumers and decomposers.
Ecosystem-Levels of studyWe can study ecology at the level of the individual, the population, the
community, and the ecosystem.
Studies of individuals are concerned mostly about physiology,
reproduction, development or behavior, and studies of populations usually
focus on the habitat and resource needs of individual species, their group
behaviors, population growth, and what limits their abundance or causes
extinction. Studies of communities examine how populations of many
species interact with one another, such as predators and their prey, or
competitors that share common needs or resources.
Energy flow
Energy enters the biological system as light energy, or photons,which is
transformed into chemical energy in organic molecules by cellular processes
including photosynthesis and respiration, and ultimately is converted to heat
energy. This energy is dissipated, meaning it is lost to the system as heat;
once it is lost it cannot be recycled. Without the continued input of solar
energy, biological systems would quickly shut down. Thus the earth is an
open system with respect to energy.
Material/Nutrient cycleElements such as carbon, nitrogen, or phosphorus enter living organisms in
a variety of ways. Plants obtain elements from the surrounding atmosphere,
water, or soils. Animals may also obtain elements directly from the physical
environment, but usually they obtain these mainly as a consequence of
consuming other organisms. These materials are transformed biochemically
within the bodies of organisms, but sooner or later, due to excretion or
decomposition, they are returned to an inorganic state. Often bacteria
complete this process, through the process called decomposition or
mineralization. During decomposition these materials are not destroyed or
lost, so the earth is a closed system with respect to elements. Those
elements whose supply tends to limit biological activity are called nutrients.
The Transformation of Energy
The transformations of energy in an ecosystem begin first with the input
energy from the sun. Energy from the sun is captured by the process
photosynthesis by producers mainly the green plants. Carbon dioxide
combined with hydrogen (derived from the splitting of water molecules)
produce carbohydrates (CHO). Energy is stored in the high energy bonds
adenosine triphosphate, or ATP .
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As it is the first step in the production of energy for living things in plants, it is
called primary production/primary producers. Herbivores obtain their energy
by consuming plants or plant products, carnivores eat herbivores, and
detritivores consume the droppings and carcasses of
all others.
Less energy is available at the herbivore level than at the primary producer
level, less yet at the carnivore level, and so on. The result is a pyramid of
energy.In general we may state that no matter how energy flows through
ecosystems there is a balance that is maintained within an ecosystem as it
always has a definite holding capacity with regard to biotic and abiotic
components which is called as homeostasis following the first and second
law of thermodynamics that state-energy can neither be created nor
destroyed only transformed from one form to the other and with each
successive energy transfer in a system, less energy is available to do work,
disorder increases.
Energy flow may be through two different food chainsGrazing and Detritus
Food chains beginning with green plants, then herbivores, and so on are
referred to as grazing food chains, because living plants are directly
consumed example plants to deer to tiger. In many circumstances the
principal energy input is not green plants but dead organic matter. These are
called detritus food chains. Examples include that on the forest
floor(putrefication of dead leaves and animals as well as their waste..
Although we have been talking about food chains, in reality the organization
of biological systems is much more complicated than can be represented by
a simple "chain". There are many food links and chains in an ecosystem, and
we refer to all of these linkages as a food web.
The Geography of Ecosystems
There are many different ecosystems: rain forests and tundra, coral reefs
and ponds, grasslands and deserts. Climate differences from place to place
largely determine the types of ecosystems we see. How terrestrial
ecosystems appear to us is influenced mainly by the dominant vegetation.
The word "biome" is used to describe a major vegetation type such as
tropical rain forest, grassland, tundra, etc., extending over a large
geographic area (Figure 3- Showing ecological demarcations on the basis of
climate). It is never used for aquatic systems, such as ponds or coral reefs. It
always refers to a vegetation category that is dominant over a very large
geographic scale, and so is somewhat broader than an ecosystem.
Conclusion:
We have seen what ecosystems are and its various aspects as well. Nature
has a wonderful way of maintaining balance such that there is space for all,
food for all, need of all etc. A web of life and its dependence on the natural
resources like, soil, minerals, water, air and others exists in nature in its most
awe-inspiring form that is the main component of ecosystem. There are
many interconnected relationships in the wild, in farming systems and even
in our backyards comprising this web of life. Due to human intervention, such
interrelationships are being affected, several species are disappearing at a
fast rate, if they are lost there will surely be a negative impact on the others.
Let us learn to appreciate the ecosystems' wonderful way of functioning and
support it rather than plunder it.
Let us rememberAll things are connected…
Humans did not weave the web of life
They are merely a strand in it
Whatever they do to the web,
They do to themselves.