Essay on :- From Biosphere to Ecological Niche !
The biosphere can be divided into a series of biogeographically regions, each inhabited by distinctive species of animals and plants. These organisms are able to move freely from place to place within each region, but not from one region to another, this being prevented by various natural barriers like river, lake, sea, mountain, desert, etc.
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Such biogeographical regions include Eurasia, South America, Africa and Australia.
Although they may possess a different fauna and flora, two such geographical regions may be virtually identical in their climatic conditions, and this is reflected in similar adaptations shown by their respective inhabitants. These equivalent areas, cutting right across different continents, are lumped together as biomes. Each biome has its unique set of conditions, and each supports a particular type of flora and fauna.
Such areas include the tundra of the Arctic and Antarctic regions; grasslands, deserts, and the different kinds of forests (coniferous, temperate and tropical). The oceans can be regarded as a single biome (the marine biome), though coral reefs are generally regarded as a separate biome. Within each biome only those organisms with the necessary adaptations for surviving the physical conditions are found.
Thus coniferous forest and tundra biomes only have organisms capable of withstanding long periods of extreme cold. Desert organisms, on the other hand, must be able to cope with intense heat and drought. Marine organisms must be able to thrive in salt water, and so on.
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Biomes are subdivided into small units called zones, each with its own particular set of physical conditions. For example, a forest biome can be divided into ground zone and canopy zone: the desert into surface and subterranean zones and the marine biome into surface, abyssal and intertidal (littoral) zones.
Individual organisms may be specially adapted to live in one of these different zones, in some cases providing them with a means of avoiding the extremes of climatic conditions met with in the biome as a whole. For example, many desert animals avoid the heat of the mid-day sun by burrowing into the subterranean zone.
Within each biome are numerous habitats, specific localities each with a particular set of conditions and an appropriately adapted community of organisms. Typical habitats include freshwater ponds, slow-flowing streams, rock pools, and hedgerows.
Within a particular habitat an organism is generally confined to a restricted situation. For example, in a slow-flowing stream, crayfish live in burrows in the river-bank, flatworms and shrimps under stones, fishes in the open water, and so on. This idea is embodied in the term ecological niche which means more than just the precise place where it lives.
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The term ecological niche embraces the organism s entire way of life, its ‘profession’, so to speak. The ecological niche of amphibians includes both aquatic and terrestrial habitats, while that of migratory birds span several biomes.