ECOSYSTEM | ENVIRONMENTAL GEOGRAPHY Optional for UPSC

Please refer to the GS notes for more information.

Definition

• According to Tansley, the ecosystem is comprised of two major parts viz. biome and habitat and thus 'all parts of such an ecosystem-organic and inorganic, biome and habitat-may be regarded us interacting factors which, in a mature ecosystem, are in approximate equilibrium, it is through their interactions that the whole system is maintained'.
• According to A. N. Strahler and A.H. Strahler (1976), 'the total assemblage of components interacting with group of organisms is known as ecological system or more simply, an ecosystem.

Types of Ecosystems

1. On the basis of habitats:

• Terrestrial ecosystems: It is ecosystems which are found on land. Examples include tundra, taiga, temperate deciduous forest, tropical rain forest, grassland, deserts.
• Aquatic ecosystems: It is an ecosystem formed by surrounding a body of water.

2. On the basis of ecoclines: 

Ecocline means a broad transition between two different ecosystems of mainly plant communities.

‘Gradient analysis’ implies the plotting of variations of plant community in particular direction and the analysis thereof and division of world ecosystem (M.J. Bradshaw, 1979).

• From mountains with relatively more moisture to the areas of increasing aridity.
• From the areas of high moisture (equatorial areas) to the areas of lowest moisture (desert).
• From lower to higher altitudes (in the Andean area of S. America).
• From equatorial hot and moist areas to cold tundra.

3. On the basis of spatial scales

• Continental Ecosystem.
• Oceanic or Marine Ecosystem.

4. On the basis of uses 

E.P. Odum (1959) has divided the world ecosystems on the basis of use of harvest methods and net primary production into two broad categories viz. 

• Cultivated ecosystems. 
• Non-cultivated or natural ecosystems.

5. On the basis of source and level of energy

E.P. Odum (1975) has classified the ecosystems into four categories on this basis.

• Unsubsidized natural solar-powered ecosystems are those which are driven by solar energy only.
• Natural-subsidized solar-powered ecosystems represent tidal estuaries, lowland forests, coral reefs etc. Solar energy is augmented to produce organic matter through primary producers.
• Man-subsidized solar powered ecosystems are those where additional energy is supplemented by human activities. 
• Fuel powered to ecosystems are represented by urban and industrial areas where fuel energy fully replaces solar energy.

6. On the basic of stages of ecosystem development:

E.P. Odum in his paper ‘the strategy of ecosystem development’,(1969) identified the following four major types of ecosystems:

• Early ecosystems.
• Mature ecosystems.
• Mixed ecosystems.
• Inert ecosystems.

Stability of Ecosystem

• Ecosystem stability means balance between input and output of energy and normal functioning of different biogeochemical cycles and stable condition of concentration of all elements. 
• It is the ability of an ecosystem to maintain a steady state (equilibrium), even after a stress or disturbance has occurred. 
• T.D. Brock (1967) has defined steady-state condition in mature ecosystem as 'a time-independent condition in which production and consumption of each element in the system are exactly balanced.
• In order for an ecosystem to be considered stable, it needs to have mechanisms in place that help it return to its original state after a disturbance occurs.
• The natural, 'normal' or 'uneventful' ecosystem attains its steady state or equilibrium condition through homeostatic mechanisms.
• Ecosystem or ecological stability is viewed in different ways as follows:
  
  • No-Oscillation stability: Stability is viewed as constancy of species numbers within a natural ecosystem.
  • Stability resilience: Stability of a natural ecosystem is ecosystem is viewed in terms of system’s capacity to withstand changes.
  • Elastic stability: Elastic stability refers to the establishment of stability in a natural ecosystem after large-scale disturbance.
  • Cyclic stability: It refers to the adjustment of a system to regular external changes.

Ecosystem Instability

• It refers to the state when an ecosystem is unable to adjust with environmental changes. 
• This so happens when the changes are continuous and enormous, and these changes exceed the resilience or capacity of the ecosystem. 
• For example, rapid rate of mass felling of trees in a forest ecosystem seldom allows regeneration of forest community because exposed surface due to deforestation is subjected to intense weathering.
• The factors responsible for ecosystem stability or instability should always be viewed in terms of ecosystem resilience. 
• If the environmental changes exceed the ecosystem resilience, ecosystem instability is caused but when the ecosystem resilience is such that it can withstand the environmental changes, ecosystem stability is maintained.
• Man has modified many of the natural ecosystems and hence has disturbed the stability of ecosystem and ecological balance through fast rate of urbanization and industrialization, mechanization of agriculture, alarming rate of deforestation etc.

Factors responsible for instability

• The ecosystem instability can occur due to natural factors such as massive volcanic eruption or climatic changes like ice age. 
• Ecosystem instability is also induced due to manmade activities. For example:
  
  • Destruction of Himalayan ecosystem due to deforestation, overgrazing etc. leading to increased weathering and erosion of soil.
  • Replacement of natural vegetation and animal species by cultivation or urban land use.
  • Introduction of exotic plant species such as water hyacinth.
  • Changing the proportion of atmospheric gases, etc.