1.3.3. Community

If we look around ourself, we will notice that 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.

Do you know?

The skies over North India are seasonally filled with a thick soup of aerosol particles all along the southern edge of the Himalayas, Bangladesh and the Bay of Bengal.- NASA research findings.

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 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.

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 organisation of the members in the community.

The characteristic pattern of the community is termed as structure which 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.

1.3.4. Ecosystem

An ecosystem is defined as a structural and functional unit of biosphere consisting of 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.

Ecosystems vary greatly in size and elements but each is a functioning unit of nature. Everything that lives in an ecosystem is dependent on the other species and elements that are also part of that ecological community. If one part of an ecosystem is damaged or disappears, it has an impact on everything else.

When an ecosystem is healthy (i.e. sustainable) it means that all the elements live in balance and are capable of reproducing themselves. Ecosystem can be as small as a single tree or as large as entire forest.

Difference between ecology, environment and ecosystem

For example, let us take Shankar IAS Academy and its students. Let’s say that ecology would be the scientific study of student’s relationship with the Shankar IAS Academy as a whole. The Shankar IAS Academy being the environment in which the student studies, and the set of circumstances surrounding the student in which environment would be the teachers, books, other students, etc are said to be ecosystem.

Components of Ecosystem

the components of ecosystem and environment are same.

1. Abiotic Components

Abiotic components are the inorganic and non-living parts of the world. The abiotic part consists of soil, water, air, and light energy etc. It also involves chemicals like oxygen, nitrogen etc. and physical processes including volcanoes, earthquakes, floods, forest fires, climates, and weather conditions.

Abiotic factors are the most important determinants of where and how well an organism exists in its environment. Although these factors interact with each other, one single factor can limit the range of an organism.

a) Energy

Energy from the sun is essential for maintenance of life. In the case of plants, the sun directly supplies the necessary energy. Since animals cannot use solar energy directly they obtain it indirectly by eating plants or animals or both. Energy determines the distribution of organisms in the environment.

b) Rainfall

Water is essential for all living beings. Majority of biochemical reactions take place in an aqueous medium. Water helps to regulate body temperature. Further, water bodies form the habitat for many aquatic plants and animals.

c) Temperature

Temperature is a critical factor of the environment which greatly influences survival of organisms. Organisms can tolerate only a certain range of temperature and humidity.

d) Atmosphere

The earth’s atmosphere is responsible for creating conditions suitable for the existence of a healthy biosphere on this planet.

e) Substratum

Land is covered by soil and a wide variety of microbes, protozoa, fungi and small animals (invertebrates) thrive in it. Roots of plants pierce through the soil to absorb water and nutrients. Organisms can be terrestrial or aquatic. Terrestrial animals live on land. Aquatic plants, animals and microbes live in fresh water as well as in the sea.

Some microbes live even in hot water vents under the sea.

f) Materials:

(i) Organic compound such as proteins, carbohydrates, lipids, humic substances are formed from inorganic compound on decomposition.

(ii) Inorganic compound such as carbon dioxide, water, sulphur, nitrates, phosphates, and ions of various metals are essential for organisms to survive.

g) Latitude and altitude

Latitude has a strong influence on an area’s temperature, resulting in change of climates such as polar, tropical, and temperate. These climates determine different natural biomes.

From sea level to highest peaks, wild life is influenced by altitude. As the altitude increases, the air becomes colder and drier, affecting wild life accordingly.

2. Biotic Components

Biotic components include living organisms comprising plants, animals and microbes and are classified according to their functional attributes into producers and consumers.

a) Primary producers - Autotrophs (selfnourishing)

♤ Primary producers are basically green plants (and certain bacteria and algae).

♤ They synthesise carbohydrate 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 nonproducers.

♤ In terrestrial ecosystem, producers are basically herbaceous and woody plants, while in aquatic ecosystem producers are various species of microscopic algae.

b) Consumers - Heterotrophs or phagotrophs (other nourishing)

♤ 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 namely micro and macro consumers.

(i) Macro consumers

♤ They feed on plants or animals or both and are categorised on the basis of their food sources.

♤ Herbivores are primary consumers which feed mainly on plants e.g. cow, rabbit.

♤ Secondary consumers feed on primary consumers e.g. wolves.

♤ Carnivores which feed on 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, monkey.

(ii) Micro consumers - Saprotrophs (decomposers or osmotrophs)

♤ They are bacteria and fungi which obtain energy and nutrients by decomposing dead organic substances (detritus) of plant and animal origin.

♤ The products of decomposition such as inorganic nutrients which are released in the ecosystem are reused by producers and thus recycled.

♤ Earthworm and certain soil organisms (such as nematodes, and arthropods) are detritus feeders and help in the decomposition of organic matter and are called det-rivores.

Classification of Eco-system: Natural Ecosystem

Fresh Water Forests Grasslands Saline Water Deserts

Terrestrial

Aquatic

♤ Marine Water

The detailed study of ecosystem will be dealt in the subsequent chapters.

Ecosystems are capable of maintaining their state of equilibrium. They can regulate their own species structure and functional processes. This capacity of ecosystem of self regulation is known as homeostasis.

Goods and Services provided by ecosystems include:

♤ Provision of food, fuel and fibre

♤ Provision of shelter and building materials

♤ Purification of air and water

♤ Detoxification and decomposition of wastes

♤ Stabilization and moderation of the Earth’s climate

♤ Moderation of floods, droughts, temperature extremes and the forces of wind.

♤ Generation and renewal of soil fertility, including nutrient cycling.

♤ Pollination of plants, including many crops Control of pests and diseases

♤ Maintenance of genetic resources as key inputs to crop varieties and livestock breeds, medicines, and other products

♤ Cultural and aesthetic benefits

Ecotone

Ecotone is a zone of junction between two or more diverse ecosystems. For e.g. the mangrove forests represent an ecotone between marine and terrestrial ecosystem. Other examples are - grassland, estuary and river bank

Ecotone

Characteristics of Ecotone

♤ It may be very narrow or quite wide.

♤ It has the conditions intermediate to the adjacent ecosystems. Hence it is a zone of tension.

♤ It is linear as it shows progressive increase in species composition of one in coming community and a simultaneous decrease in species of the other out going adjoining community.

♤ A well developed ecotones contain some organisms which are entirely different from that of the adjoining communities.

♤ 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 organisms which occur primarily or most abundantly in this zone are known as edge species. In the terrestrial ecosystems edge effect is especially applicable to birds.

For example the density of birds is greater in the mixed habitat of the ecotone between the forest and the desert.

Niche

A niche is the unique functional role or place of a species in an ecosystem. It is a description of all the biological, physical and chemical factors that a species needs to survive, stay healthy and reproduce.

A niche is unique for a species, which means no two species have exact identical niches. Niche plays an important role in conservation of organisms.

If we have to conserve species in its native habitat we should have knowledge about the niche requirements of the species and should ensure that all requirements of its niche are fulfilled.

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.

Do you know?

Two Schemes namely Nagar VanaUdyanYojana and School Nursery Yojana have been launched. Nagar VanaUdyanYojana aims to create at least one city forest in each city with a minimum area of 25 ha. The scheme aims at creation of a City Forest in forest areas within their jurisdiction up to a maximum of 100 ha and minimum area of 20 ha. The objective of the Yojana is to create 200 City Forests in the country. The School Nursery Yojana aims to build a lasting bond of students with nature.

1.3.5. Biome

BIOME Distribution based on Temperature and Precipitation

The terrestrial part of the biosphere is divisible into enormous regions called biomes, which are characterized, by climate, vegetation, animal life and general soil type.

No two biomes are alike. The climate determines the boundaries of a biome and abundance of plants and animals found in each one of them. The most important climatic factors are temperature and precipitation.