• Ecology ‘Oikos’ meaning home or place to live in and ‘logos’meaning study.
  • Ecology is defined “as a scientific study of the relationship of theliving organisms with each other and with their environment”.


  • The main levels of organization of ecology are six and are as follows.



  • Organism is an individual living being that has the ability to act or function independently. It may be plant, animal, fungi etc. It is a body made up of organs, organelles or other parts that work together to carry out on the various processes of life.
  • Population is a community of interbreeding organisms (same species), occupying a defined area during a specific time.
  • Population growth rate is the percentage variation between the numbers of individuals in population at two different times. Therefore the population growth rate can be positive (birth and immigration) or negative (death and emigration)
  • Communities in most instances are named after the dominant plant form.
  • For example, a grassland community is dominated by grasses, though it may contain herbs, trees, etc.
  • Types of Community : On the basis of size and degree of relative independence communities may be divided into two types
  • Major Community
  • These are large sized and relatively independent.
  • They depend only on the sun’s energy from outside. E.g.  tropical evergreen forest in the North-East
  • Minor Community
  • These are dependent on neighbouring communities and are often called
  • They are secondary aggregations within a major community. E.g. A mat of lichen on a cow dung pad.
  • An ecosystem is a community of organisms interacting with each other and with their environment such that energy is exchanged and system-level processes, such as the cycling of elements, emerges.
  • It includes plants, trees, animals, birds, fish, water, soil, micro-organisms and people.
  • Everything that lives in an ecosystem is dependent on the other species and the elements that are also part of the ecological community. If one part of ecosystem is damaged or disappears, it has an impact on everything else.
  • Ecosystem can be as small as single tree or as large as entire forest.
  1. BIOME
  • A biome is a large naturally occurring community of flora and fauna occupying a major habitat. E.g. Rainforest biome or tundra biome.
  • Plants and animals in a biome have common characteristics due to similar climates and can be found over a range of continents.
  • Biomes are distinct from habitats because any biome can comprise a variety of habitats.



  • Biosphere is a part of the earth where life can exist. Biosphere represents a highly integrated and interacting zone comprising of atmosphere (air), hydrosphere (water) and lithosphere (land).
  • The biosphere includes all living organisms on earth, together with the dead organic matter produced by them.
  • The biosphere is absent at extremes of the North and South poles, the highest mountains and the deepest oceans since existing hostile conditions there do not support life (life is the characteristic feature of the biosphere).
  • Occasionally spores of fungi and bacteria do occur at a great height beyond 8,000 metres, but they are metabolically inactive, and hence represent only dormant life.



  • An ecotone is an area that acts as a boundary or a transition between two ecosystems.
  • A common example could be an area of marshland between a river and its riverbank.
  • Ecotones are of great environmental importance. Because the area is a transition between two ecosystems or biomes, it is natural that it contains a large variety of species of fauna and flora as the area is influenced by both the bordering ecosystems.
  • Examples of ecotones include marshlands (between dry and wet ecosystems), mangrove forests (between terrestrial and marine ecosystems), grasslands (between desert and forest), and estuaries (between saltwater and freshwater).

A) Characteristics of Ecotones

  • It may be wide or narrow.
  • It is a zone of tension (as it has conditions intermediate to the bordering ecosystems).
  • It could contain species that are entirely different from those found in the bordering systems.
  • Ecotones can be natural or man-made. For example, the ecotone between an agricultural field and a forest is a man-made one.

B) Ecocline

  • Ecocline is a zone of gradual but continuous change from one ecosystem to another when there is no sharp boundary between the two in terms of species composition.
  • Ecocline occurs across the environmental gradient (gradual change in abiotic factors such as altitude, temperature (thermocline), salinity (halocline), depth, etc.).

C) Edge Effect & Edge Species

  • Edge effects refer to the changes in population or community structures that occur at the boundary of two habitats. Generally, there is a greater number of species found in these regions (ecotones) and this is called edge effect.
  • The species found here are called edge species.



  • Niche refers to the unique functional role and position of a species in its habitat or ecosystem.
  • It is a description of all the biological, physical and chemical factors that a species needs to survive, stay healthy and reproduce.
  • Niche id unique for a species i.e. no two species have exact identical niche.

A) Types of Niche

  1. Habitat niche – where it lives
  2. Food niche – what is eats or decomposes &what speciesit competes with.
  3. Reproductive niche – how and when it reproduces.
  4. Physical & chemical niche – temperature, land shape,land slope, humidity & other requirement.

B) Difference between Habitat and Niche


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