FOOD CHAIN AND FOOD WEB

                                                                            FOOD CHAIN

            The transfer of food energy from the producers through a series of organisms (herbivores to carnivores and then to decomposers) with repeated eating and being eaten, is known as food chain.

            The solar energy is trapped in the ecosystem by the green plants and produce energy rich carbohydrates. These green plants are known as primary producers. The green plants are eaten by plant eaters (herbivores) also called primary consumers. Herbivores are in turn eaten by meat eaters (carnivores) also called secondary consumers. Secondary consumers in turn may be still eaten by other carnivores which are known as tertiary consumers. After decay of both plants and animals simpler compounds are being released into the atmosphere due to the activity of decomposers which are re-utilized by green plants.

            In nature, we generally distinguish two types of food chain – Gazing food chain and Detritus food chain.

            Example – A food chain in grassland ecosystem starts with grasses and goes through grasshoppers, the frogs, the snake and finally the hawks.

            Grasses ---------------- Frogs --------------- Snakes --------------- Hawks

            A detritus food chain starts with the dead plants and animals and goes through (fungi, bacteria, protozoa), (insect larvae, fishes, molluscs), (small fishes), (large fishes) and finally the )large fishes and birds).

            Fungi                           Insect larvae                                                     Large fishes

            Bacteria ---------------- Fishes ---------------- Small fishes ------------- Birds

            Protozoa                       Molluscs

FOOD WEB

            Food chains in ecosystems are found to be interconnected and usually form a complex network with several linkages and are known as food webs. Thus, “food web is a network of food chains where different types of organisms are connected at different trophic levels, so that there are a number of options of eating and being eaten at each trophic level.”

            For example – In an Antarctic ecosystem resemble the total ecosystem including the Antarctic sea and the continental land. The land does not show any higher life forms of plants. The only species are that of some algae, lichens and mosses. The animals include penguins and snow petrel which depend upon the Antarctic chain for their food energy.

            Food web gives greater stability of the ecosystem. In a linear food chain, if one species becomes extinct or one species suffers then the species in the subsequent trophic levels are also affected. In a food web, on the other hand, there are a number of options available at each trophic level. So if one species is affected, it does not affect other trophic levels so seriously.

            Consider the simple food chains of Arctic tundra ecosystem.

            Cladonia ------------ Reindeer ------------- Man

            Grass ---------------- Caribou ---------------Wolf

            If due to some stress, the population of reindeer of Caribou falls, it will leave little option for man or wolf to eat from the ecosystem. Had there been more biodiversity, it would have led to complex food web giving the ecosystem more stability.

            SIGNIFICANCE OF FOOD CHAINS AND WEBS

            1. Food chains and food webs play a very significant role in the ecosystem because the two most important functions of energy flow and nutrient cycling take place through them.

            2. The food chains also help in maintaining and regulating the population size of different animals and thus, help maintain the ecological balance.

            3. Food chains show unique property of biological magnification of some chemicals. There are several pesticides, heavy metals and other chemicals which are non-biodegradable in nature. Such chemicals are not decomposed by micro-organisms and they keep on passing from one trophic level to another. And, at each successive trophic level, they keep on increasing in concentration. This phenomenon is known as biomagnifications or biological magnification.

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ECOSYSTEM - COMPONENTS OF AN ECOSYSTEM, BIOTIC AND ABIOTIC COMPONENTS

            Ecosystem may be defined as a natural, functional, ecological unit comprising living organisms and their non living environment that interact to form stable, self supporting system.

            COMPONENTS OF AN ECOSYSTEM

            Components of an ecosystem can be classified into two major divisions – Biotic and Abiotic components.

            1. Biotic Components:- All living organisms present in the environment are included within the biotic component. The biotic components can be sub divided into three major groups –

            a) Producers – These includes all the autotrophic green plants which can make their own food with the help of sunlight. Besides these some organisms like Cyano-bacteria and some Chemo-systhetic bacteria can produce their own food, which are also included in producers.

            b) Consumers – These includes all heterotrophic organisms which depend on plants and other organisms for food and nutrition. Based on the food they eat, consumers are again sub-divided into three groups – Herbivores (Plant eaters; e.g., – Rabbit, deer, cow, goat, etc.), Carnivores (Meat eaters; e.g., – Tiger, lion, fox, etc.) and Omnivores (Both plant and meat eaters; e.g., – Man, bear, etc.)

            c) Decomposers – These are mainly bacteria and fungi that obtain their food form organic materials of dead plants and animals and decompose the complex organic molecules into simpler ones which can be readily used up by green plants again.

            2. Abiotic Components:- The non-living matters constitute the abiotic components of an ecosystem. It includes physical and chemical components like climatic factors, edaphic (soil) factors, geographical factors, energy, nutrients and toxic substances.

            a) Physical factors:- The sunlight and shade, intensity of solar flux, duration of light hours, average temperature, annual rainfall, wind, latitude and altitude, soil type, water availability, water currents, etc., are some of the important physical features which have a strong influence on the ecosystem.

            b) Chemical factors:- Availability of major nutrients like carbon, nitrogen, phosphorous, potassium, hydrogen, oxygen and sulphur, level of toxic substances, salts causing salinity and various organic substances present in the soil or water largely influence the functioning of the ecosystem.

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ENVIRONMENTAL STUDIES AS MULTIDISCIPLINARY SUBJECT

            The science of environment studies is a multidisciplinary science because it depends on various disciplines like chemistry, physics, medical science, etc. It is the science of physical phenomena in the environment. It is inherently a multidisciplinary field that draws upon not only its core scientific areas, but also applies knowledge from other non-scientific studies such as economic, law and social science.

            1. In the field of physical science it helps to understand the flux of material and energy interaction. It also helps to construct mathematical models of environment.

            2. Environmental study is related with chemical science in the sense that it helps in understanding the molecular interactions in the system.

            3. In the field of biological science it describes the effects within the plant and animal kingdom and their diversity. 

            4. In the field of atmospheric science, environmental studies deals with the examination of the phenomenology of the Earth's gaseous outer layer with emphasis upon interrelation to other systems. It comprises meteorological studies, greenhouse gas phenomena, airborne contaminants, sound propagation phenomena related to noise pollution, and even light pollution. 

            5. Environmental studies is very much related to ecological studies. It helps to analyse the dynamics among an interrelated set of populations, or a population and some aspects of its environment. The study of endangered species, predator interactions, effects upon populations by environmental contaminants, or impact analysis of proposed land development upon species viability, etc.

            6. In environmental chemistry environmental studies deals with the study of chemical alterations in the environment; principal areas of study include soil contamination and water pollution; the topics of analysis involve chemical degradation in the environment, multi-phase transport of chemicals and chemical effects upon biota.

            7. The relation of environmental studies with Geo-science includes environmental geology, environmental soil science, volcanic phenomena and evolution of the earth's crust. In some classification systems, it can also embrace hydrology including oceanography. 

            8. In the field of mathematics and computer Science it will help in environmental modeling and analysis of environment related data.

            9. Environmental studies is also related with Economics. It deals with economical aspects of various components of environment.

            10. In Law it helps in framing of environment related laws, Acts, rules and their monitoring.

            11. In the field of Social Science it helps in dealing with population and health related issues. 

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