CONCEPT OF ECOSYSTEM
The term ecosystem was first used by Sir Arthur Tansley (1935), as a basic unit of ecology. The word is a combination of ‘eco' meaning environmental and 'system' standing for an interacting and interdependent complex. Such an ecological system or ecosystem implies a unit of area in which all the living organisms (plants, animals and microbes) interact among themselves and also maintain a functional relationship with the physical features of their non-living environment(things like air, water and mineral soil). The biotic and abiotic components of the ecosystems are interrelated and interdependent on each other and together contribute to the smooth functioning of the system.
Each system depicts a characteristic biotic diversity supported by regular flow of energy and cycling of materials. All the co-existing and independent populations of living organisms (biotic component) of an area constitute a ‘community’. The ecosystem can therefore also be defined as a functional system of a community and its environments. Other names used for an ecosystem include ‘Biocoenosis’, ‘Geobiocoenosis’ and ‘Microcosm’.
TYPES OF ECOSYSTEMS
The ecosystem can be very small consisting of a predator and prey or a host and its parasites. It can be as small as a village pond. These small ecosystems are generally connected to other lower and higher organizations to constitute a larger ecosystem. The ecosystem can be very large stretching over hundreds of kilometers. The biosphere, including all the inhabitants of the earth, forms the largest known ecosystem. Some of the other major ecosystems are seas, rivers, deserts grasslands and forests.
Ecosystems can be classified into two categories:
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Natural ecosystems
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Man-made or artificial ecosystems
The examples of artificial ecosystems are cultivation of crops, maintenance of poultry, a piggery and an apiary of honeybees. Such ecosystems are maintained through artificial means i.e., through outside addition of energy and planned administration. The natural ecosystems, on the contrary, work under natural conditions independent of any interference by man. For the sake of convenience, natural ecosystems can be further subdivided into :
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Terrestrial ecosystems including grasslands, deserts and forest ecosystems
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Aquatic ecosystems comprising ponds, lakes, rivers and
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Marine ecosystems such as seas, oceans, estuaries etc.
COMPONENTS OF AN ECOSYSTEM
As already stated, each ecosystem comprises two separate components viz., biotic (living) and abiotic (non-living). The abiotic components of any ecosystem are the properties of the environment, the biotic components are the life forms that occupy a given ecosystem. The relationship between the biotic and abiotic components of the ecosystem is called holocoenosis.
ABIOTIC COMPONENTS
Abiotic components of the ecosystem pertain to non-living elements which may be of the following types.
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Inorganic substances: These substances include essential elements like water, carbon, sulphur, phosphorus and so on which are present in the bodies of the organisms as well as outside their bodies. These are continuously exchanged between the living and the non-living parts and their amount present in the ecosystem indicates what is technically called as ‘standing state’ or ‘standing quality’ of the ecosystem.
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Organic substances: The important organic substances in the ecosystem include carbohydrates, proteins, lipids and humic substances which are distributed like the inorganic substances.
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Physical Factors: These include such factors which have a direct bearing on the organisms of a particular area. Out of these, light energy is the most important used in the photosynthesis by the green plants. The other notable factors are temperature, wind and humidity.
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Edaphic Factors: These are related to the structure and composition of the soil including its physical and chemical properties, like soil and its types, soil profile, minerals, organic matter, soil water, soil organisms.
BIOTIC COMPONENTS
It comprises the living part of the environment, which includes the association of a number of interrelated populations belonging to different species in a common environment. The populations are that of animal community, plant community and microbial community.
Every living organism is in some way dependent on other organisms. Plants are food for herbivorous animals, which in turn are food for carnivorous animals. Thus, there are different tropic levels in an ecosystem. Some organisms such as fungi live only on dead material and in-organic matter. They are grouped in terms of the means they use to get energy. The biotic components of the ecosystem mainly comprise the categories of producers and consumers which are usually named as autotrophs and heterotrophs respectively, due to self nourishing habit of the former and dependent nourishing in the latter category. The role of the three categories is explained below.
- PRODUCERS (AUTOTROPHIC COMPONENTS) :These include all the green plants which fix light energy and utilize simple inorganic substances for the manufacture of complex materials. The process is referred as photosynthesis. Plants produce their own energy without consuming other life forms: plants gain their energy from conducting photosynthesis via sunlight. Autotrophs form the basis of any biotic system.
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CONSUMERS (HETROTROPHIC COMPONENTS) : There are generally animals feeding on other organisms. Consumers exist on the next level of the food chain. There are three main types of consumers: herbivores, carnivores and omnivores. Herbivores feed on plants. Carnivores get their food by eating other carnivores or herbivores and omnivores can digest both plant and animal tissue. These organisms, also known by the name of macro-consumers or phagotrophs, include all the animals which feed directly or indirectly on the green plants and thus utilize and rearrange the complex materials manufactured by the autotrophs. Another important group of consumers is that of defritritvores which consume organic detritus produced by the autotrophs and collected at the bottom.
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DECOMPOSERS (SOPROTROPHS) : Decomposers like bacteria and fungi consume waste and living things that have died. These are those hetrotrophicmicro-organisms which decompose the complex compounds in the dead organic matter and chiefly include bacteria and fungi. They are also called as micro-consumers, saprotrophs, saprobes or saprophytes. Their main functions are to release inorganic substances which are then used by the producers i.e. plants. An accidental forest fire serves as a quick method of decomposition by burning the biota and thus converting the chemical compounds into simpler substances and elements.