Ecology – Chapter 1 Shankar IAS

What is meant by Ecology

  1. Defined “as a scientific study of the relationship of the living organisms with each other and with their environment.

History of Ecology

  1. The classical texts of the Vedic period such as the Vedas, the Samhitas, the Brahmanas and the Aranyakas-Upanishads contain many references to ecological concepts
  2. The Indian treatise on medicine, the Caraka- Samhita and the surgical text Susruta-Samhita.
    contain a classification of animals on the basis of habit and habitat, land in terms of nature of soil, climate and vegetation; and description of plants typical to various localities.
  3. Caraka- Samhita contains information where air, land, water and seasons were indispensable for life and that polluted air and water were injurious for health.
  4. The environment is defined as ‘the sum total of living, non-living components; influences and events, surrounding an organism.

Components of Environment

1. Abiotic – Energy, Radiation, TEMP, Water, etc.
2. Biotic– plants, animals, man, DECOMPOSER ETC.

Six main levels of organization of ecology are,

1. Individual– Organism is an individual living being that has the ability to act or function independently.
2. Population-Population is a group of organisms usually of the same species, occupying a defined area during a specific time,
3. Community– Communities in most instances are named after the dominant plant form (species). A community is not fixed or rigid; communities may be large or small.

Types of Community

(a) Major Community

  • These are large-sized, well organized, and relatively independent.
  • They depend only on the sun’s energy from outside and are independent of the inputs and outputs from adjacent communities.
  • E.g: tropical ever green forest in the North-East

(b) Minor Communities

  • These are dependent on neighbouring communities and are often called societies.
  • They are secondary aggregations within a major community and are not therefore completely independent units as far as energy and nutrient dynamics are concerned.
  • e.g: A mat of lichen on a cow dung pad.

4. Eco-System-

  • An ecosystem is defined as a structural and functional unit of biosphere consisting of a community of living beings and the physical environment, both interacting and exchanging materials between them.
  • It includes plants, trees, animals, fish, birds, micro-organisms, water, soil, and people.

Components of Ecosystem

The components of the ecosystem are categorized into

abiotic – (non-living things) and Biotic (living beings).

Abiotic Components (Non-Living things)

  • Consists of soil, water, air, and light energy etc.
  • Also includes chemicals like oxygen, nitrogen-, etc. and physical processes including volcanoes, earthquakes, floods, forest fires, climates, and weather conditions.

a) Energy b) Rainfall c) Temperature d) Atmosphere e) Substratum f) Materials (i) Organic compound (ii) Inorganic compound g) Latitude and altitude

Biotic Components (Living things)

Biotic components include living organisms comprising plants, animals, and microbes and are

 1. Primary producers – Autotrophs

  • Primary producers are basically green plants (and certain bacteria and algae).
  • They synthesize carbohydrates from simple inorganic raw materials like carbon dioxide and water in the presence of sunlight by the process of photosynthesis for themselves and supply indirectly to other non-producers.

2. Consumers — Heterotrophs 

  • Consumers are incapable of producing their own food (photosynthesis).
  • They depend on organic food derived from plants, animals or both.
    Consumers can be divided into two broad groups

2a. Macro consumers

  • They feed on plants or animals or both
  • Herbivores feed plants e.g. cow, rabbit.
  • Secondary consumers feed on primary consumers e.g. wolves.
  • Carnivores feed secondary consumers are called tertiary consumers e.g. lions which can eat wolves.
  • Omnivores are organisms which consume both plants and animals e.g. man.

2b. Micro consumers – Saprotrophs 
They are bacteria and fungi which obtain energy and nutrients by decomposing dead organic substances (detritus) of plant and animal origin. (Ex: Earth Worm)

Characteristics of Ecotone

  • It may be very narrow or quite wide.
  • It has the conditions intermediate to the adjacent ecosystems.
  • Zone of tension.
  • Sometimes the number of species and the population density of some of the species is much greater in this zone than either community. This is called Edge effect
  • The organism which occurs primarily or most abundantly called Edge Species.

Types of Niche

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


  • Is a part of the earth where life can exist.
  • represents a highly integrated and interacting zone comprising of atmosphere (air), hydrosphere (water) and lithosphere (land)
  • Life in the biosphere is abundant between 200 metres (660 feet) below the surface of the ocean and about 6,000 metres (20,000 feet) above sea level.
  • absent at extremes of the North and South poles.
  • Living organisms are not uniformly distributed throughout the biosphere

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