NIRMALA AGARWAL

The place where an organism lives is known as habitat. The term habitat is more specific environment. Habitat constitutes a part of the total environment of that region. It must offer to an organism shelter, food and congenial climatic conditions which will be well-suited for the organism to survive, reproduce and flourish. In other words, a place where suitable conditions for the existence of an organism prevail is the habitat of that organism. For example, the habitat of a fish may be a lake, pond, river, sea or other aquatic systems. The habitats of cacti and camel are sandy, dry, hot deserts. Snowbound, extremely cold Polar Regions are the natural habitats of polar bears. The habitat of Indian rhinoceros is grassland and forest area of the foothills of the Himalayas in Central Nepal and some pockets of plains of west Bengal and Assam. Red blood corpuscle of human blood is the habitat of the malarial parasite (plasmodium).

If we say that fishes live in water and monkeys live in forests, it would not be adequate. Freshwater fishes cannot live in sea water and vice versa. Bonnet monkeys and langurs are found only in the tropical forests of South India, Sri Lanka, Burma, Thailand, Malay, and Singapore. These forests offer to these monkeys a habitat with specific climate, woods, plants and other animals to interact with. The habitat of a tiger must have small animals for the tiger to hunt and feed upon. It should also include thick vegetation in the form of shady trees and shrubs where the tiger can hide and wait for its prey. These conditions form the biotic components of a habitat of tiger. Thus the Himalayan tiger can only live in the Himalayan forests and the Bengal tigers in the Sunderbans. These tigers cannot live in the rocky mountains of North-West America.

Each habitat comprises abiotic or nonliving components and biotic or living components.

Abiotic components include:

1. Climatic factor such as temperature, light, rainfall, wind, gases, etc.
2. Edaphic factors such as soil texture, soil pH, soil nutrients, etc., and
3. Physiographic or topographic factors like altitude, exposure of slopes, steepness, etc.

Living or biotic components also include all living organism like plants, animals and microbes present in the habitat.

Ecological Niche

You must keep in mind that any habitat would generally support more than one form of life. For example, the Himalayan forests serve as a habitat not only for the Himalayan tigers but also for many other organisms. A river supports not only fish but many other organisms like frog, aquatic plants, mosquito larvae, insects, etc. The term habitat is not concerned with what the organism does (how it behaves, transform energy, responds to changing environment, etc). But ecological niche includes not only the specific space occupied by an organism but also its functional role in the ecosystem. The term habitat should not be confused with niche, which means actual role of an organism where it is best fitted. Biologically, the habitat is the organism’s address and the niche is its profession.

Microhabitats

A habitat is usually a large area within which there may be many smaller units. These constitute the microhabitats. The conditions present in one region can be quite different from those in another region. In a sea, various plants and animals can be seen in different zones and regions. Some specific plants and animals present at the bottom are different from those present at the surface. The biotic and biotic factors present in the different regions of the sea are different. This is why the organisms present in the deep water of the sea are not found at the surface. All these areas constitute different microhabitats. Microhabitat is a small, specialized and effectively isolated area which is not based on the size of the population. Microhabitat may be as a forest or as small as a single leaf.

Let us consider the example of land. The climatic conditions in one region of the land are quite different from those in another region. Within a country like ours, the climate, the type of water. The soil conditions, the nutrients and other factors vary from place to place. This is why the plants and animals found in Kashmir are different from those in Madras. The banana and coconut that grow so luxuriantly in Kerala are not seen in Ladakh. The common field rats of the Indian plains of Uttar Pradesh are not found in the deserts of Rajasthan. The desert rat of Rajasthan has different habit and behavior. It is smaller in size, prefers to come out only at night, does not need much water and burrows deep in the ground. Thus you see that the desert rats are better adapted to the microhabitat of Rajasthan desert than to the Indian plans.

1. Observe the crevices between the rocks if found near your locality. Do you find same living things? This place actually acts as a microhabitat for those living forms found there.

2 go to a nearby shallow pond. Get a piece of small stone from the bottom. Observe carefully do you see small plants attached to it?

Types of habitat

Basically the entire world may be divided into three spheres-the atmosphere (air), the lithosphere (earth), and the hydrosphere (water). The part of earth where life exists is known as biosphere. In other words, the whole zone of air, land, and water at the surface of the earth occupied by living beings is called biosphere.

Our environment is extended up to a height of about 1,600 kilometers but living organisms are confined to a very thin area. The total thickness of life containing and life supporting environment of the world i.e., biosphere, is about 16 km. into includes about 8 km in air and 8 km in water from the earth surface. The biosphere has three major types of habitats.

1. Terrestrial habitat (land)
2. Aquatic habitat (water)
3. Aerial or arboreal habitat (air or tree)

1) Terrestrial Habitat

The word terrestrial has been derived from a Latin word terra which means ground. Organisms that live and move on land are called terrestrial organisms. The terrestrial habitat is marked by rapid fluctuations in temperature, moisture and climate. This habitat is not uniform as there are many barriers like deserts, Mountains Rivers, etc., on it. The light factors of terrestrial habitat fluctuate with the season and the altitude. Life on land is sustained by air, soil temperature, and rainfall. Some commo9n terrestrial organisms are trees, ferns, elephant, camel, man, etc.

2) Aquatic Habitat

The word aquatic has been derived from the Latin word aqua which means water. Organisms which live in water are known as aquatic organisms. These organisms live and breed or propagate in water. They are classified as freshwater organisms, if they inhabit a river, pond, lake, stream, etc; marine organisms are those which live in sea water [marines (French) Means Sea]. Freshwater habitats may be subdivided into lentic and lotic types. Standing or stagnant bodies of water like ponds, lakes, reservoirs and bogs are the examples of lentic habitats, while moving or running waters like rivers and streams are the representatives of lotic habitats. The well known aquatic organisms are algae, small animals and fishes.

Freshwater animals do not survive in the sea. Do you know why? The water of freshwater pond and river is not salty. Freshwater organisms have higher concentration of salts in their bodies than in the surrounding water. Sea and ocean waters contain high percentage of salts. Freshwater organisms would lose water from their body if placed in marine water. If marine organisms are placed in freshwaters, their body will swell because of entry of excess water in their body.

On a glass slide take a few filaments of Spirogyra (pond silk). Put a drop of water and cover it with a cover slip. Observe under a microscope. Now put some salt water over the Spirogyra filament after removing the cover slip. Observe the changes. You will find the reason why freshwater organisms don not survive in marine water.

3)  Aerial or Arboreal Habitat

The Latin word Arbor means trees or its branches. A number of animals are tree dwelling (arboreal) like monkeys and squirrels. Air is not a suitable medium to support life. Actually no organism originates in air, although some aquatic and terrestrial organisms have become secondarily adapted to aerial existence. The organisms that use air (sky) for their activities are known as aerial (Volant) organisms viz, bats, birds and insects.

There are some organisms which can use both water and terrestrial systems as their habitat. They are called amphibious (Greek word amphi means on both sides and bios means life). Examples are frog and toad. They can use both water and land as their habitat. Their life cycle is not completed in one habitat alone. Frogs go to water for laying eggs. Note down the names of all the organisms you see in yo9ur locality. Group them as terrestrial, aquatic, arboreal, amphibious, etc. count the types of organisms in each group.