best ias books

Ecology, Biome, Ecotone, Niche, Ecosystem, Biosphere


  • Ecology may be defined as the scientific study of the relationship of living organisms with each other and with their environment
  • The emphasis is on relationships between organisms and the components of the environment namely abiotic (non-living) and biotic (living).
  • Ecology is derived from 2 Greek words
  • Oikos >> Home or place to live in
  • Logos >> Study
  • Literally, it means study of home or nature
  • Ecology not only deals with the study of the relationship of individual organisms with their environment, but also with the study of populations, communities, ecosystems, biomes and biosphere as a whole



  • a large community unit, characterized by a major vegetation type and associated fauna, found in a specific climatic region
  • No 2 biomes are alike




  • Transitional area between two biomes or diverse ecosystems (where two communities meet & integrate)
  • Examples : between a field and forest, between forest and grassland
  • may appear as a gradual blending of the two communities across a broad area, or may manifest itself as a sharp boundary line
  • May contains some organisms which are entirely different from that of adjoining communities
  • Sometimes the number of species & population density of some of the species is much greater in this zone than either community, Known as edge effect
  • Organisms which occur primarily or most abundantly in this zone are known as edge species



  • Description of all the biological, physical & chemical factors that a species needs – to survive, stay healthy & reproduce
  • Niche is unique for every species which means no 2 species can have exact identical niche



  • A functional unit of nature encompassing complex interaction between its biotic (living) and abiotic (non-living) components.
  • For example- a pond is a good example of ecosystem; (it can also be as small as a single tree)
  • Components of ecosystem: They are broadly grouped into:-
  • Abiotic
  • Biotic components


Natural ecosystems - Ecosystems dependent on solar radiation & energy subsidies (alternative sources) such as wind, rain and tides E.g. tropical rain forests, tidal estuaries and coral reefs

Man-made ecosystemsDependent on solar energy + Dependent on fossil fuel


Lotic (Moving water) — Lentic (Stagnant water)


  • Represents a highly integrated & interacting zone comprising of atmosphere, hydrosphere & lithosphere
  • abundant life between 200 meters below oceans surfaces till approx. 6000 meters above sea surfaces
  • absent at extremes of north & south poles, the highest mountains & at the deepest oceans majorly due to hostile conditions
  • Occasionally spores of fungi & bacteria do occur at great height beyond 8000 meters but they are not metabolically active & hence represent only dormant life
India Yearbook English India Yearbook Hindi Economic Survey 2017

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