Definitions : Ecology, Environment, Ecological hierarchy


Branch of biology, concerned with relations of organisms to one another (energy & mineral cycling) and their physical surroundings (environment). Ecology encompasses study of individuals, organisms, populations, communities, ecosystems, biome & biosphere forming various levels of ecological organization.


Environment is biotic (living organisms) & abiotic (non-living organisms) surrounding an organism or population. It includes factors that influence their survival, development and evolution. Environment is our basic life support system. It provides the air we breathe, the water we drink, the food we eat and the land where we live. 


Cell is the basic unit of life in any living organism; likewise, an individual/organism is the smallest unit of interaction or existence in the ecological arena.

  • Organism or single individual: An organism is a single individual or being. Ex. an elephant in Kaziranga.
  • Species: Group of single individuals having potential to inter-breed & produce fertile offspring. Ex. Entire elephant population.
  • Population: It is a group of individuals of a plant or an animal species inhabiting a given area. Ex. All Elephants of Kaziranga form a population of elephants in that area.
  • Biological community: Assemblage of populations of plants, animals, microbes and all other life forms living in a particular area and interacting with each other for fulfilment of needs. Ex. Elephants+ rhino+ bacteria+ other wild animals and plants of Kaziranga. Biological community does not involve interactions of living beings with an abiotic/physical environment.
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  • Ecosystem: Composed of biological community, integrated with its physical environment through exchange of gases, energy & recycling of nutrients. Ecosystem involves interactions between living and non-living worlds or biotic and abiotic worlds.
  • Landscape: A unit of land with a natural boundary having a mosaic of patches representing different ecosystems. Ex. a view of river, its valley & grasslands nearby from a mountain top with three different ecosystems in one picture.
  • Biome: A large regional unit characterised by major vegetation types and associated fauna/animal life, found in a specific climatic zone. Ex. Tropical rain forests of Western Ghats form a typical biome with characterised vegetation of mahogany, ebony, rosewood etc. accompanied by animal life of Malabar civet, Nigiri Tahr etc. and climatic conditions of high rainfall, high humidity and higher temperatures.
  • Biosphere: On a global scale, all the earth’s terrestrial biomes & aquatic systems constitute the biosphere. It includes the lower atmosphere, land, oceans & rivers etc. where living organisms can be found. So, biosphere is the biologically inhabited part of earth along with its physical environment.
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