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Ecosystem instability / Ecological Niche

Ecosystem instability refers to that state when an ecosystem is unable to adjust with environmental changes. The happens when the changes are continuous and enormous and these changes exceed the resilience or capacity of the ecosystem. The factors responsible for ecosystem stability or instability are always viewed in terms of ecosystem resilience. If the environmental changes exceed the ecosystem resilience, ecosystem instability is caused but when ecosystem is such that it can withstand environmental changes, ecosystem stability is maintained.
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,
(1)   Destruction of Himalayan ecosystem due to deforestation, overgrazing etc. leading to increased weathering and erosion of soil.
(2)   Replacement of natural vegetation and animal species by cultivation or urban land use.
(3)   Introduction of exotic plant species such as water hyacinth.
(4)   Changing the proportion of atmospheric gases, etc.

Ecological Niche
Ecological niche refers to the functional role and position of a species in relation to other species in the given ecosystem. In a natural ecosystem, several species of plant and animal communities perform different roles in getting food and thus each community is confined to certain locality having certain functions. Such locality having ideal environmental conditions for the survival of a species is called niche. The species of a given niche may not service in other niches. The ecosystem stability depends upon diversity of a niche. Greater the niche diversity, greater the stability of ecosystem. The ecosystem becomes unstable if one or more species are eliminated because then niche becomes empty and other species which were dependent on the eliminated species food now become vulnerable to elimination.

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