Chapter III Chapter - III Basic Ecological Principles Components of Ecosystem: Biotic Components and Abiotic Components (with info-graphics) The term ecosystem was coined by A.G. TansIey (1935) who stated the following words, “………………… the more fundamental conception is………….. the whole system (in the sense of physics), including not only the organism complex but also the whole complex of physical factors forming what we call the environment of the biome – the habitat factors in the widest sense. Though the organisms may claim out primary interest, when we are trying to think fundamentally we cannot separate them from their special environment which they form one physical system. It is the systems so formed which…………………..are basic units of nature on the face of the earth……………….. The ecosystems as we may call them are of most various kinds and sizes”. Thus, the ecosystem can be of any size. It has been observed that the green plants and some autotrophic bacteria are able to prepare their own food by utilizing solar radiant energy (light). They are capable of binding up the simple molecules of carbon-dioxide, water and other elements, such as, nitrogen, phosphorous, potassium, magnesium etc. by the help of light. These substances are confined to the physical surroundings. Some animals (herbivores) eat plants directly and others (carnivores) eat such animals, which feed on the plants. Another group of organisms depends on the dead plants and animals to obtain their food from the decomposed tissues. The food is digested and assimilated to synthesize different organic compounds from which the energy is derived for the life activities. The mechanism involves two distinct processes, firstly, the energy used by the plants passes through various organisms and finally it is lost as heat. The process has been referred as the ―flow of energy‖. Secondly, along with energy, the substances also pass through the organisms but remain available for use, again and again. This process is known as biogeochemical cycling. These two 1 | P a g e Chapter III processes bind the organisms to their environment and the complex network is termed as the ecosystem. An ecosystem in a laboratory may be as small as an aquarium. It may range from the size of a lake or forest to the size of the earth. Biosphere (W. Vernadsky 1929) or the Ecosphere (L.C. Cole, 1958) is the usual term which applies to the ecosystem that covers the whole of the earth. In fact, none of the ecosystems in independent, rather all are interdependent in some way or other. All ecosystems consist of two major components—biotic and abiotic. The biotic component is comprised the living organisms, whereas the abiotic component includes the physical (non- living) environment. But, both of these components interact very closely to exhibit a definite structural organization. Sometimes, it is very difficult to separate the biotic components from the abiotic components. Biotic Component: When we consider the biotic components, the organisms are divided into two categories, the autotrophs and the heterotrophs. The autotrophs can produce their own food. They are the green plants with chlorophyll and certain types of bacteria—chemosynthetic and photosynthetic. Since these organisms produce food for all other organisms, they are also known as ‗Producer‘. The heterotrophs depend directly or indirectly on the autotrophs for their food. This type of organisms is further divided into two groups, such as, Photographs and Osmotrophs. 2 | P a g e Chapter III The photographs take food from outside and digest it inside their bodies. They are called consumers. All animals—herbivores (plant eating), carnivores (animal eating) or omnivores (eating all kinds of food) fall in this group. The osmotrophs are those organisms who secrete digestive enzymes to break down the food into simpler substances and then absorb the digested food. This group embraces the parasitic and saprophytic bacteria as well as the fungi. They may also be called Decomposers because their role has been well documented in the decomposition of the dead organic matter. But the most interesting point is that all of these parasites are not decomposers, rather some of them are consumers (insects and such small animals) who help in the decomposition by breaking down the dead organic matter into small bits. However, the heterotrophs can also be divided into two broad groups as the bio phages (feeding on living organisms) and the sarcophagus (feeding on dead organisms) Fig. 10.3. The above mentioned divisions of organisms are principally based on the nature of food which in turn gives rise to the trophic structure of the ecosystem. It signifies a step-wise systematic relationships among the living organisms for food, which forms a chain, known as the food chain. Some common food chains can be illustrated as follows: (i) Grass ———–> goat———–>man (ii) Seed———–>rat——— > cat———–>hawk 3 | P a g e Chapter III (iii) Algae———–>zooplankton ———–> fish———–>man (iv)Algae———–>insect———–> frog———–> snake———–>peacock Such food chains can be traced back to the Producers and the position of the organism in the food chain is indicated by the trophic levels. This trophic level is defined as the number of links by which it is separated from the producer; the producers always belong to the first trophic level or the base. A single species can operate more than one trophic level in the ecosystem which means that this species get its food from more than one source. Again, the same species may be eaten by several other species of a higher trophic level; thus, one can find out several food chains linked together in an intersecting manner to develop a network, known as food web. Such a network provides a clear- cut idea about the functioning of the ecosystem. Abiotic Component: Abiotic component of ecosystem refers to the physical environment and its several interacting variables which can be divided into four folds: (i) Lithosphere which means the solid mineral matter on the earth and the land form as well; (ii) Hydrosphere, i.e. the water in oceans, lakes, river, ice-caps, etc.; (iii) Atmosphere, the gaseous mixture in the air; and (iv) The radiant solar energy. The position and movement of the earth with its gravitational force are additional components of the environment Fig. 10.4. However, these components create invariability of magnitude and duration of other environmental factors. 4 | P a g e Chapter III The energy interacts with rocks, water and gases to produce a complex environment with a large number of identifiable variables such as heat, light, rain, wind, snow, fog, dust, storm, fire, etc. Thus, by the interaction of variables, the environment is created and maintained as a unit where any single component cannot be removed or altered without disturbing the other components. Therefore, the environment is a dynamic whole, which remain continuously in a state of flux and also varies in space. The structural analysis of the environment in an ecosystem is urgently required to know the energy gradients and their flow. Functionally the ecosystem allows the flow of energy and cycling of materials which ensures the stability of the system and continuity of life. The energy needed for all life processes come from solar radiation Fig. 10.5. 5 | P a g e Chapter III During photosynthesis, green plants convert light energy to chemical (potential) energy and make it available to other organisms as food. Thus, a continuous flow of energy from sun through organisms maintains the life on earth. Laws of Thermodynamics govern on the transfer and transformation of energy. It says, the energy can never be destroyed, but it is transformed into different forms. Therefore, the part of solar radiant energy that is not used in photosynthesis is used in heating of air, water and soil. So some change does occur in cyclic order of nature. Ultimately the energy is reflected back to outer space as heat. In fact, a small fraction of available light energy is utilized during photosynthesis and a very little part is stored in animal tissues; the bulk is wasted as heat. The next point is the ratio between the production and assimilation of energy. The small organisms utilize a large part of the assimilated energy for growth while larger organisms consume a larger part of the assimilated energy for maintenance of the organism (respiration). However, all these mechanisms-the transformation of energy, the food chain, the assimilation etc., are expressed as ecological efficiency. 6 | P a g e Chapter III It is therefore clear that the two processes, namely the flow of energy and the cycling of materials are equally important for the functioning of ecosystem. These two processes are inseparable and run concurrently. As a consequence of interactions, a variety of organic substances are produced. This production is called biological production, which is essentially different from the chemical and industrial production. Biologists are interested in this production as it a part of a perpetual process. In dealing with ecosystem, the concept of community is very important which can be defined as an assemblage of a number of organisms including man. The organisms include several species, which occupy the same habitat. Even the micro-organisms are the part of a community. Here, ‗community‘ is essentially treated as a biotic component of the ecosystem. A population may also be defined 7 | P a g e Chapter III ecologically as a group of organisms of the same species occupying a particular space. However, population is the basic unit of the community—an aggregate of individuals of same species who mate among themselves. Naturally the members live in a common area and like to use the same resources of the particular ecosystem.