Shankar IAS Environment PDF For UPSC

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Shankar IAS Environment 8th Edition

Ecology ‘Oikos’ means home or place to live in and ‘logos’ means study. Literally, it is the study of the home of nature.

Ecology is defined “as a scientific study of the relationship of the living organisms with each other and with their environment.” It deals with the ways in which organisms are moulded by their environment, how they make use of environmental resources including energy flow and mineral cycling


The roots of ecology lie in Natural History, which is as old as human civilization itself. Since early history, man has indulged in ecology in a practical sort of way, knowingly and unknowingly. In primitive societies every individual was required to have an intimate knowledge of his environment for their survival, i.e., about the forces of nature and of plants and animals around him/her.

Our ancient Indian texts have references to ecological principles. The classical texts of the Vedic period such as the Vedas, the Samhitas, the Brahmanas, and the AranyakasUpanishads contain many references to ecological concepts. The Indian treatise on medicine, the Charaka-Samhita, and the surgical text Sushruta-Samhita show that people during this period had a good understanding of plant and animal ecology.

These texts contain the classification of animals on the basis of habit and habitat, land in terms of nature of the soil, climate, and vegetation; and description of plants typical to various localities. Charaka- Samhita contains information that air, land, water, and seasons were indispensable for life and that polluted air and water were injurious to health.


Everything that surrounds or affects an organism during its lifetime is collectively known as its environment. The environment is defined as ‘the sum total of living, non-living components; influences and events, surrounding an organism.

All organisms (from viruses to man) are obligatorily dependent on the other organism and the environment for food, energy, water, oxygen, shelter, and other needs. The relationship and interaction between organisms and the environment are highly complex. It comprises both living (biotic) and non-living (abiotic) components. The environment is not static. Both biotic and abiotic factors are in flux and keep changing continuously.

For instance: Let’s take the environment of a fish in the pond. External environment of fish

• Its environment consists of abiotic components such as light, and temperature, including the water in which nutrients, oxygen, other gases, and organic matter are dissolved.

• The biotic environment consists of microscopic organisms called plankton which it assumes as well as aquatic plants, animals, and decomposers.

• It is enclosed by the outer body surface.

• The internal environment is relatively stable as compared to the external environment.

• However, it is not absolutely constant. Injury, illness, or excessive stress upsets the internal environment.

• For example, if a marine fish is transferred to a freshwater environment, it will not be able to survive.


An individual Organism is an individual living being that has the ability to act or function independently. It may be a plant, animal, bacterium, fungi, etc. It is a body made up of organs, organelles, or other parts that work together to carry out the various processes of life.

A population is a group of organisms usually of the same species, occupying a defined area during a specific time. The population growth rate is the percentage variation between the number of individuals in a population at two different times. Therefore the population growth rate can be positive or negative.

The main factors that make population increase are birth and immigration. The main factors that make the population decrease are death and emigration. The main limiting factors for the growth of a population are abiotic and biotic components.

Population density is the relation between the number of individuals in a population and the area they occupy. 1.3.3. Community If we look around us, we will notice that the population of plants and animals seldom occur by themselves.

The reason for this is quite obvious. In order to survive, individuals of any one species depend on individuals of different species with which they actively interact in several ways. For eg: Animals require plants for food and trees for shelter. Plants require animals for pollination, seed dispersal, and soil microorganism to facilitate nutrient supply.

Communities in most instances are named after the dominant plant form (species). For example, A grassland community is dominated by grasses, though it may contain herbs, shrubs, and trees, along with associated animals of different species. A community is not fixed or rigid; communities may be large or small.

Types of Community On the basis of size and degree of relative independence communities may be divided into two types: (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 evergreen forest in the North-East (b) Minor Communities These are dependent on neighboring 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.

Structure of a community In a community the number of species and size of their population vary greatly. A community may have one or several species. The environmental factors determine the characteristic of the community as well as the pattern of organization of the members in the community.

The characteristic pattern of the community is termed as a structure that is reflected in the roles played by various population, their range, the type of area they inhabit, the diversity of species in the community, and the spectrum of interactions between them

Language English
No. of Pages435
PDF Size34.5 MB

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