Six major ecosystems of the world are as follows: 1. Fresh Water Ecosystem 2. Marine (Ocean) Ecosystem 3. Grassland Ecosystem 4. Forest Ecosystem 5. Desert Ecosystem 6. Cropland Ecosystem.
In the world, there are several ecosystems working at macro or micro level. As pointed out earlier, the biosphere is the biggest ecosystem which combines all the ecosystems of the world.
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But with the difference in physiographic, climate, natural vegetation, soil and water bodies, separate ecosystems have been developed as depicted in Figure 2.10.
The above classification of ecosystems is more geographical, but from the approach of ‘habitat’ there are several micro-ecosystems working in a geographical region. The regions represent the biomes, which has been defined by Odum thus: “Regional climates interact with regional biotic and substrate to produce large, easily recognisable community units, and called biomes.”
These are primarily the biotic zones also referred to as major life zones. Table 2.1 indicates the characteristics of the major environmental zones/biomes of the world whereas the major areas have been depicted in Figures 2.11, 2.12 and 2.13.
The major ecosystems are described as under:
1. Fresh Water Ecosystem:
Fresh water habitats can be divided into two categories:
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(i) Standing water or lentic (calm)—lake, pond, swamp or bog.
(ii) Running water or lotic (washed)—river, spring, stream.
Although fresh water habitats occupy a small portion of the earth’s surface, they are of great importance to humankind because they provide drinking water as well as water for domestic and industrial needs. Odum has defined fresh water ecology as: “Fresh water ecology emphasises the organisms in environment relationship in the freshwater habitat in the context of the ecosystem principle.”
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A pond is a good example of fresh water ecosystem, which exhibits a self-sufficient, self-regulating system. A pond is a place where living organisms not only live but also interact with abiotic and biotic components, thus forming an ecosystem which is different from other systems.
Similarly, lakes, swampy regions and delta regions of rivers have their own ecosystems in which producers, consumers and decomposers interact and are responsible for the unique ecosystem of each.
2. Marine (Ocean) Ecosystem:
The marine ecosystem is different from fresh water ecosystem mainly because of its salty water and also because:
(i) The sea covers 70 per cent of earth’s area,
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(ii) The sea is deep,
(iii) The sea is continuous, and
(iv) The sea water is in continuous circulation. According to Odum, “marine ecology emphasises the totality or pattern of relationship between organisms and the sea environment.”
In a marine ecosystem, the ecology of shallow and deep waters as well as estuarine part is different from each other. Each ocean in itself represents a very large and stable ecosystem
3. Grassland Ecosystem:
Grasslands occupy about 19 per cent of the earth’s area, which include tropical and temperate grasslands. In this, the savannah ecosystem is very important.
The abiotic components are the nutrients present in the soil and aerial environment. The elements like carbon dioxide, water, nitrates, phosphates, sulfates, etc., are present in the air and soil of the area.
The producers are mainly grasses and small trees and shrubs. The primary consumers include cows, buffaloes, sheep, goats, deer, rabbits, and other animals, while secondary consumers are animals like foxes, jackals, snakes, frogs, lizards, birds, etc.
The microbes are active in the decaying and dead organic matter of different forms. They bring the minerals back to the soil, thus making them available to producers. Pastoralism and livestock ranching are the main occupations in these regions.
4. Forest Ecosystem:
About 30 per cent of the land area of the earth is under forest cover, but due to man’s intervention this area is gradually becoming smaller. But still forest ecosystem is very important.
The coniferous forests stretch as broad belts across North America and Eurasia. On the other hand, temperate deciduous forests occupy areas in eastern North America, parts of Europe, Japan and also in Australia. Among forests the tropical evergreen forests are found in the tropical regions.
In the forest ecosystem, the abiotic components are the organic substances present in the soil and atmosphere and also minerals present in dead organic debris. The producers are trees of different species.
The primary consumers are animals of various types, while secondary consumers include carnivores like lions, tigers, snakes, birds, Hazards, foxes, etc.
The forest ecosystems are of great concern from the environmental point of view. The rate of exploitation of forest by man is growing day by day, thus causing a great concern to all nations of the world because of its impact over global climate and on several animal species.
5. Desert Ecosystem:
Deserts generally occur in regions having less than 25 cms of rainfall and are unevenly distributed.
Scarcity of rainfall may be due to:
(i) High sub-tropical pressure, as in the Sahara and Australian deserts,
(ii) Geographical position in rain shadows, or
(iii) High altitude as in Tibetan, Gobi, Bolivia deserts.
There are three life forms of plants that are adapted to deserts:
(i) The annuals, which avoid drought by growing only when there is adequate moisture,
(ii) The succulents, such as the cacti, which store water, and
(iii) The desert shrubs, which have numerous branches and a special root system which help them to adapt to desertic conditions.
The most common animals, apart from camels and goats, are reptiles and insects, able to live under xeric conditions. Due to poor vegetation, dead organic matter is less and some fungi and bacteria act as decomposers.
Apart from hot desert, there are also widespread cold deserts encircling the north and south poles, where permanent ice caps have developed an entirely different type of ecosystem, sustainable to cold climatic conditions.
6. Cropland Ecosystem:
Apart from above mentioned natural ecosystems, there are also man-engineered ecosystems. One such ecosystem is the cropland ecosystem, in which man has developed croplands after considering the soil, climatic and other environmental conditions. These are ecosystems of dominant crop species like wheat, maize, jowar, paddy, sugarcane, cotton, tea, coffee, etc.
The abiotic components of this ecosystem include climatic conditions and mineral contents of the soil. In case of any deficiency man used chemical fertilizers and/or water for irrigation, etc. The various types of food grains, pulses and commercial crops are grown in these croplands, which provide food and fodder not only to man and animals, respectively, but in the fields several types of animals like birds, rats, rabbits, and other smaller reptiles insects, etc., also survive.
The decomposition of dead organic matter of plants and animals make the minerals available again. There is a need that every ecosystem should be studied in detail. Apart from above mentioned macro or global ecosystems, there are several meso and micro regions existing in each region.
For example, India has the following major ecosystems:
1. Himalayan mountain ecosystem
2. Plain ecosystem
3. Desert ecosystem
4. Central India plateau ecosystem
5. Peninsular (Deccan plateau) ecosystem
6. Coastal plain ecosystem
7. Island ecosystem
These ecosystems have been identified on the basis of physiography, which also controls climate, natural vegetation, soil and also man’s adoption to nature.
Each major region can be divided into sub-ecosystem regions; for example, Rajasthan has the following ecosystems:
(i) Arid ecosystem
(ii) Irrigated arid ecosystem
(iii) Sub-arid ecosystem
(iv) Aravalli hills ecosystem
(v) Eastern plains ecosystem
(vi) Hadoti plateau ecosystem
Further identification of micro-ecosystems will help not only in understanding the ecosystem but also in regional development and planning. The goal of sustainable development can only be achieved, when our developmental policies are based on the micro-ecosystem of each region.