Nature is beautifully balanced. Each living thing has its own place, role and special utility. All organisms live in harmony with each other and with their environment. They also have special relationships among themselves and interact with each other in different ways.

In this lesson you will learn the various aspects of such relationships.

After completing this lesson you will be able to :

• define the terms environment, ecology, population, community, food chain, food web, ecosystem and biosphere.
• state that the ecosystem are the units of biosphere.
• list the factors in an ecosystem and categorise them into abiotic and biotic factors.
• list the various trophic categories of organisms.
• state that an ecosystem can exist only if energy source is available to it.
• cite an example of a food chain and define the different trophic levels in it.
• explain the need and the methods to preserve the natural ecosystems.
• describe the overall changes in environment due to rapid growth of human population and the industrialisation in India.

Environment: It is the aggregate of the various living and non-living objects, events and influences in the midst of which a living organism lives. All organisms depend upon the environments for their survival. A close interaction between the two is essential to meet the basic necessities of life. Organisms depend on many things from their environment viz. energy, water, oxygen, food, shelter and their mates.

The environment of a living organism consists of two components : (1) a living or biotic component which includes all other living organisms (microbes, plants and animals) and (2). a non-living or abiotic component (also called the physical environment). This includes the soil, land or water, light, temperature, humidity and rainfall of the areas in which the organism lives.

The study of the relationships of the living organisms to each other and their surroundings is called Ecology. The term 'ecology' was first used by the German biologist Ernest Haekel in 1869 and is derived from the Greek roots 'Oikos' meaning a 'house' or 'living-place' and 'logos' meaning the study or 'science of. An Ecologist of today adopts a holist approach in which a whole picture is built up which is more important than its parts.

Look at the given picture of a forest (fig. 34.1) and study its physical environment and the relationship that exists between the living organisms that live there.

Make a list of the plants that are found there starting from grass and other herbs to shrubs and trees.

Observe the animals shown in the picture. Which of these are the plant eaters and which the flesh eaters ? You will realise that all the plant eaters (herbivorous) will compete with each other for grass and other plants as food and all the flesh eaters (carnivorous) will compete amongst themselves to eat the herbivores. Thus we will find competition between members, of the same species (infra-specific competition) and also amongst members of different species (inter-specific competition) (fig. 34.2 a, b). There will also be prey-predator "eating and being eaten" relationships. Different predators may compete among themselves for a common prey and so on. You will learn about many more kinds of relationships that exist in an ecosystem as you study Ecology-further.

Think of the same forest with deer living in it. There would be a group of certain number of deers of this particular species living in this area—this is the population of deers. Similarly, there would be a population of tigers or a population of wolves or a population of cows, or even a population of the deodar or any other trees growing in that forest and, of course, the population of the common grass in this forest.

In the same forest, members of several species of both plants and animals are living together on different relationships. These collectively make up the biotic community of that forest.

Habitat is the place where an organism normally lives. It is 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, e.g. Frog's habitat is pond, deer's habitat is forest and so on.

Niche is the field of activity of an ogranism in its habitat. Biologically the habitat is the organism's address and the niche is its professional or functional role.

Organism (individuals)->Population-»Community ->Ecosystem->Biomes ->Biosphere

Any structural and functional unit of the environment that can be identified and studied is called an ecosystem. An ecosystem can be natural or artificial, temporary or permanent; examples of artificial (man-made) ecosystems are an aquarium, a plantation, an orchard or a park.

There occurs a "flow of energy" and cycling of matter between living and non-living components of the ecosystem, (fig. 34.3)

Non-living or Abiotic Component is mainly divided into soil or water, and climate. Soil and water contain a mixture of inorganic and organic nutrients. In aquatic ecosystem salinity is also an important factor. Climate includes, variables like light, temperature and rainfall which determine the type of living organisms that can flourish in that ecosystem.

The Biotic Component : On the basis of nutrition living organisms can be divided into Autotrophic and Heterotrophic organisms. All organisms fit into these two categories. Autotrophs synthesise their own organic requirements (food) from simple inorganic molecules through photosynthesis using Light as source of energy. They are green plants and act as Food producers. Heterotrophic organisms require a source of organic food (prepared by the autotrophs) which supplies them with chemical energy. They are called consumers. Heterotrophs are thus dependent on autotrophs for their existence and an understanding of their relationships is essential to an understanding of ecosystems. Food supplies both energy and materials for the sustenance of life.

Herbivores such as deer, cattle and goat which feed directly on green plants are called First Order (Primary) Consumers, the smaller Carnivores as Second Order (Secondary) and the larger Carnivores like the tiger, lion etc. as the Third Order (Tertiary) Consumers.

Decomposers : The non-green organisms like the fungi and some bacteria, which are incapable of producing their food, live saprophytically on the dead and decaying plants of animal bodies and break them down into simpler substances. Such substances are thus returned to the environment and are once again available to the green plants for producing new protoplasm. These organisms are called decomposers. (Fig. 34.4)

Scavengers : These are the carrion-eaters i.e. those that feed on the dead bodies of animals. Fox, Jackals, Vultures, Kites etc. are some common scavengers of grasslands and forests. Even small sized insects - the beetles, ants, etc. eat dead flesh. A variety of fish and tortoises in rivers and seas are scavengers. Do you know that some carrion eating fishes feed on dead bodies of humans disposed off in the rivers ?

(i)          A pond is an ecosystem -in which :

(ii)     The sea is an ecosystem in which :

        Green algae in the upper layers produce the food at the first level. The herbivorous fish, snails, and a variety          of other animals are primary consumers, the bigger fish are the secondary consumers and so on.

A forest is an ecosystem in which :

If the source of Radiant Energy (the sun) is not there or the food producers are missing, things come to a stand still.

An artificial Ecosystem (Aquarium)

An aquarium is a glass container with water. It has soil with some water plants rooted in it. A few fish roam about within its walls. You could even have a couple of snails in it. And, the most important is the electric bulb providing the light energy for the aquatic plants to produce food. The food chains are established in it. The CO₂ given out by fishes is used by the green plants to produce food in light and the oxygen given out by the plants is used by the fishes ft)r respiration. The excreta of fish provides nutrients in the soil for the plants. Some decomposers (bacteria) may be present in the soil to break down the dead organic matter (for Example broken or dead leaves). Thus an aquarium is a balanced ecosystem.(Fig.34.5)

In an ecosystem, the energy -containing organic, molecules produced by autotrophic organisms are the source of food (materials and energy). For heterotrophic organisms e.g. a plant is eaten by an animal which in turn may be eaten by another animal. In this way energy is transferred through a series of organisms, each feeding on the preceding organism and providing raw materials and energy for the next organism. Such a sequence is called food chain. Each stage (link) of the food chain is known as a trophic level.

The primary producers (green) constitute the first trophic level, the primary consumers (herbivores) constitute the second trophic level and the secondary consumers (carnivores) constitute the third trophic level and so on.

Primary producers of aquatic ecosystems are algae, often the unicellular ones which form the phytoplanton (tiny floating plants) of the surface layers of oceans and lakes. In terrestrial ecosystems the primary producers are advanced plants (ferns, gymnosperms and flowering plants) which form forests and grasslands.

Primary consumers are the herbivores which include insects, reptiles, birds and grazing mammals.

In aquatic ecosystems (fresh water and marine) the herbivores are typically small crustaceans and molluscs.

Secondary and tertiary consumers feed on herbivores and are therefore carnivores. These may be predators which hunt, capture and kill their prey; carrion feeders which feed on dead bodies or parasites which live on their hosts and are smaller than them.

Study Fig. 34.6- This is more or less the same as Fig. 34.4 but with some specific examples of living beings like plants (maize), goat, lion and man.

Given below are three food chains :

(i) Maize -> Man.

(ii) Maize—» Goat—> Man

(iii) Maize—> Goat—> Lion

• Starting point in each food chain is Maize (a green plant, the producer). It traps solar energy to make protoplasm.
• Man in food chain :

1. is the primary consumer, but in food chain
2. he is the secondary consumer.

• Goat in both food chains (ii) and (iii) will be a primary consumer. Can it be called a secondary consumer in any other situation ?

Some other food chains are as follows :

Grass —>grasshopper-» lizard —>crow

Grass ->grasshopper —>frog-> snake-> peacock

(In a pond) : Diatoms —> amoeba -> small aquatic insects —> large aquatic insects —> small fish —> large \fish.

In an ecosystem food chains are never so simple and isolated because any one organism is eaten by a number of predators. So the food chains become inter-linked and complex to form a "food web".

Food webs : You know what is a "web". This is what a spider spins with its "thread" crossing and intercrossing in various directions. Similarly, the food chains in a community may cross each other at several points. Look at fig.34.7. it shows a still more complex food web in Gir forest (home of lion in Saurashtra). Label the several alternative foods for each predator.

Do you think that a small sized animal can chase a large one, kill it and eat it ? No, that is not possible. So a predator is always larger than its prey. Only a herbivore (primary consumer) at times may be smaller than the plant, for example the insects eating leaves of large trees.

Pyramid of numbers : The number of individuals of the prey which are killed and eaten by a single predator to sustain its life is always high. For example, a snake would feed may be on some hundreds of frogs in its life time, and each frog in its turn would have devoured hundreds of grasshoppers. So how many grasshoppers have ultimately supported the life of a single snake (surely, several thousand). This kind of relationship of numbers of different levels of food chains can be represented by a pyramid of numbers with a single animal at the top.

Fig. 34.,8. represents a pyramid of numbers in a certain food chain. Here we have shown an imaginary pyramid divided into "floors" (food levels) and the kind of organisms at each level. The number of individuals of the food species goes on decreasing at each higher level.

Just like the food chains, the pyramids of numbers are also not so simple and isolated. This is because the consumers at each level may eat a variety of prey.

Energy flow in a food chain : Every organism eats (or prepares its own food as the green plants) for two purposes firstly, for obtaining "energy" for its activities and secondly, for obtaining body-building material for growth and repairs.

Fig.34.9 represents energy flow through one simple food chain. One very important point to note in it is that no organism at any level is able to pass on to the next higher level all the energy that it received from the lower level. Some important points to remember are as follows :

• The green leaves are able to make use of only 1% of the energy falling on it. Out of every 1000 calories falling

on it, 990 calories are lost into the atmosphere by radiation, and only 10 calories are used in making glucose.

• When a herbivore (e.g. deer) eats these plants, then out of the 10 calories which the deer received, 9 are lost to

These considerations about energy How in a food chain are generalized in what is called "10 Per cent Law".

By now, you -have understood that every ecosystem is balanced and self dependent as long as all its components are functioning properly. According to its size and kind, an ecosystem can support only a limited number of organisms in it. This is called its carrying capacity. Removal of any one component disturbs the balance of the entire ecosystem. Let us see how.

Suppose there is grass land. If any one factor like the sunlight or the atmospheric carbon dioxide is removed, then no food is produced and herbivores will starve to death, and so will also the carnivores. That means the life in this grass land will come to an end. If suppose the same grass land has sunlight as well as carbon dioxide but all the carnivores are removed from it, in that situation the herbivores will become so numerous that they will eat away all the grass which in turn will bring starvation and death of these herbivores to a stand still situation till a fresh balance between the grass and grass eaters is acquired.

Natural ecological groupings of plants and animals extend over, large areas. Each of these major aquatic land ecosystems or distinctive aquatic terrestrial areas with their typical plants and associated animals are called BIOMES. A biome is the largest terrestrial community or a major ecosystem.

The major ecosystems of the. world are oceans, deserts, grasslands, forests etc

1. Tundra                                             1.Estuarine biome
2. Coniferous forests                         2. Coastal wetland biome
3. Temperate Forests
4. Tropical rain forests
5. Grasslands
6. Deserts.

The different ecosystems are united to form the Biosphere or Bcosphere, which includes living organisms and the physical environment with which they interact. Thus the oceans, surface of the land and lower parts of the atmosphere all form part of the ecosphere. The word "Biosphere" means the sphere of living things on earth. It extends upto 6 kilometers above the sea level (on mountain tops) and upto 7 kilometers below the sea level in (deep oceans).

Our earth can be regarded as a big ecosystem with its vast oceans, grasslands, forests, deserts, mountains, lakes and valleys. All these are inhabited by their own typical flora (plants) and fauna (animals) and subjected to changes in temperature, varying rainfall and other climate factors. All was well for a very long time with the natural vegetation and wild life thriving and man living peacefully enjoying the bounties of nature and in harmony with nature. Early man was a creature of the environment and derived his requirements like any other animal; with the gradual development of his civilisation he has become a moulder of the environment. He has changed the biosphere from a self-sufficient life supporting system into a mere system of resources for himself. The rapid rise in the human population has led to over exploitation of the natural resources leading to depletion of productive land, soil erosion, silting of rivers, energy crisis and many wild animals becoming extinct. Deforestation is a great threat to our

economy, quality of life and environment.

Human activities have posed another serious threat to the world's environment and that is by causing pollution and degrading air, water and soil. Air is polluted by poisonous fumes containing SO₂, CO, CO₂ oxides of nitrogen and various hydrocarbons given out by industries. Air pollutants cause serious respiratory and vascular diseases, damage vegetation and buildings. Water is polluted by community waste water, sewage and wastes from industrial and agricultural activities. A large number of serious infectious diseases of the gastrointestinal tract are spread through contaminated water. Water pollution is harmful to aquatic life and disturbs the food chains and food webs in water.

You will read more about pollution and the measure to check it in a later lesson. Man must realize his responsibility towards keeping the environment clean for mankind and the future generations. In this context the slogan " Save the planet earth, it is the only one we have" is a very appropriate one, because the survival of the human race is at stake.

• All that surrounds an organism is its environment.
• The environment includes many abiotic (non-living) factors and many biotic (living) factors.
• Abiotic factors include light, temperature, rainfall, humidity, water and soil.
• Biotic factors include microbes, plants and animals (all other living organisms).
• Ecology is the study of relationships between the living organisms and their environment.
• Population is a group of individuals of the same species living in an area.
• Community is a group of mutually adjusted plants and animals living in an area.
• The biotic community together with the physical environment forms an interacting svtem called Ecosystem.
• Radiant energy and the producers are the primary requisites in any ecosystem.
• A pond, lake, forest, sea are examples of natural ecosystems.
• School aquarium with fishes and plants is a small man-made ecosystems; other man-made ecosystems are parks, plantations and orchards.
• Ecosystems contain several food chains with a producer, a primary consumer and secondary or even tertiary consumers.
• A food chain is the sequence of organisms in which each organism eats the preceding member and is eaten by the succeeding member.
• Several interconnecting and intercrossing food chains form food webs.
• The number of individuals at any one level on a food chain is less than the individuals at the lower level. The highest level has the smallest number. This produces a kind of pyramid of numbers.
• Energy flows from producer to the higher categories of consumers and only 10 percent energy is available to the next higher level from its lower one, in a food chain.
• An ecosystem can support only a limited number of organisms, this is called its carrying capacity.
• Biomes are the major ecosystems of the world, dominated by a particular kind of climate, plants and animals.
• Biosphere is the sphere of living things. It is the part of the earth and the atmosphere which contains life. It extends between 6 kilometers above and 7 kilometers below the sea level.
• Various ecosystems are the units, of biosphere.
• Man is disturbing natural ecosystem, and is causing environmental pollution.

1. Giving one example of each member in the pair and distinguish between:

2. Write a food chain with three trophic levels

3. Give reasons for the following:

        (i)  There is competition between members of the samespecies.
       (ii)     Only 10% energy;is available to the. next higher level from its lower one in a food chain.
      (iii)     Ecosystems are considered to be units of the biosphere.
     (iv)      Deforestation is said to damage the ecosystem.
      (v)     Air and water pollution are a cause foreserious concern.

4. Give two examples each of the following :-

Carnivore, herbivore, habitat, predator, parasite.

5. List any three ways in which man has disturbed the natural ecosystems.

1. Environment includes all those things which surrounds an organism and affects its life.

3.     (i) Deer and wolf
        (ii) Deer and other deers living in the same territory.
        (iii) Rabbits and goats or cow and buffalo.

4.     (i) Group of individuals of the same species occupying a given area.
        (ii) Group of mutually adjusted plants and animals inhabiting a natural area.
        (iii) A place where an organism normally lives.
        (iv) Field of activity of an organism in that habitat.

1. The biotic community together with the physical environment forms an interacting system called the ecosystem.

2. A. Pond, forest and sea; B. aquarium.

3.     (i) CO₂ is used by green plants to produce food in the presence of light. If there is no CO₂ no food will be      
            produced.

       (ii) They breakdown complex compounds of dead bodies into simpler ones which return to the surroundings                or become available to the green plants for producing new protoplasm.

4. If all the food producers are removed from the ecosytem all the consumers will die.

1.     (i) a. grass —> grasshop —>snake—> Peacock —> Tiger b. Maize—> Rabbit—>Tiger

       (ii) Grasshopper, rat, squirrel, moth, rabbit

      (iii) Tiger.

2. Pattern of several interconnected food chains.

3. The pyramid formed by the number of organisms at different trophic levels of a food chain is called pyramid of numbers.

4. The number of organisms that can be supported by an ecosystem is called its carrying capacity.

5. There is an energy loss as we go from one level of a food chain to its next higher level, because only 101% of the energy is passed on, 90% is lost to the atmosphere by radiation.

1. Biosphere is the sphere of living things on earth, it extends to a maximum of 6 km. height above and 7 km. Below the sea level.

2. Biome is a larger ecosystem dominated by a particular kind of climate.

3. Tundra, coniferous forests, terperate forests, tropical rain forests, grass lands, deserts.