I UNIT 10 :BASIC CONCEPTS '

Structure 10.1 Introduction Objectives 10.2 10.3 Ecosystem and its Structure 10.3.1 The Biotic Component 10.3.2 The 10.4 Functions of an Ecosystem 10.4.1 Food-Chain nnd Food-Web 10.4.2 Trophic Levels 10.4.3 Energy, Sources of Energy andEnergy How 10.4.4 Biogeochemical Cycles 10.5 The Concept of and 10.6 The Concept of Homeostasis 10.7 Types of 10.8 Summary 10.9 Key Words 10.10 Further Readings 10.1 1 Answers to SAQs

10.1 INTRODUCTION The purpose of this unit is to make clear some of the basic concepts in ecology. After defining what is ecology, we will also outline the fundamental structure of an ecosystem. We will study how each ecosystem has an abiotic (non-living) and a biotic (living) component and how there is a continuous interaction among these two components. In each ecosystem there are producer organisms and organisms. Producers generate food with the help of solar energy while all the consumers are directly or hldirectly dependent on these producers, for food. There are different kinds of food-chains and we will outline some examples in this unit. Energy passes along the food-chain in each ecosystem - it is a one-way traffic. We will, however, note that the various minerals continuously circulate between the abiotic and biotic components of the ecosystem. These are the so called biogeochemical cycles. We will then try to follow the concept of ecological niche and also the concept of homeostasis. Objectives I After studying this unit, you should be able to describe the components of an ecosystem, elaborate upon the biotic and abiotic components and the interaction between them, explain the food-chains, food-web and in an ecosystem, outline various biogeochernical cycles, and explain the concept of ecological niche as well as the concept of homeostasis.

10.2 ECOLOGY Ever since the time of Greek philosophers, there is considerable written material that is definitely ecological. Man must have been using his ecological knowledge since time immemorial. This must have been important for his survival in the wild environment. Even today many tribal people all over the world are using this ecological knowledge and living happily in the wilderness. With the tremendous increase in population, every one including you, must understand ecology more thoroughly. This is essential for our survival and well being. The word ecology was recently coined by a Gerrnan biologist Emst Haeckel, in 18.69. This word has a Greek root oikos meaning 'house'. Thus, an ecologist actually.studiesthe organisms 'at home'. For the sake of definition we will call ecology as the study of relationship of organisms to their environment or surrounding. It really inclu&sThe study of the structure and function of . Right here you must note that human being is also another organism and study of his environment is equally part of ecology. Broadly speaking, ecology can be subdivided into two major branches (1) autecology, and (2) synecology. When you are studying one organism and its relationship with the surrounding environment, you are doing autecological study. Study of groups of organisms which are associated together as a unit is the realm of synecology. For example, you are interested in a particular snake and you want to find out where it lives, what it eats, how many eggs does it lay, etc., you are pursuing autecology. On the other hand, if you are interested in a particular river, the kind of terrain it is flowing through, the kinds of fishes and other animals as well as plants that are found in the river, the inter-relationshipof plants-animals and physicochemical factors of water, etc., then the objective is synecological. Both these aspects are important but the synecological studies give total picture of the situation. Of course, much efforts and time are also required to complete synecological work. The autecological approach is relatively straightforward but by no means easy or simple. Study of ecology is becoming more and more important as we are modifying the environmpt surrounding us. Here, the word environment is used broadly to denote everything that surrounds us -that is it includes other living organisms as well as non-living things. This and subsequent units will give you sufficient idea about the basics of ecology and its usefulness in day to day planning for economic development.

10.3 ECOSYSTEM AND ITS STRUCTURE To study ecology, one has to take a s&er unit ipd this unit is called as ecosystem. Ecosystem is a basic unit of ecology. For example, Grassland ecosystem, Forest ecdsystem , . Ecosystem is defined as structural and functional unit of ecology. This means, each such system has a defdte structure and each smcture associated with an ecosystem has a definite role to play in the functioning of an ecosystem. Each ecosystem is made up of living organisms and their surrounding non-living components. These two parts of an ecosystem are therefore, called as living (biotic) and non-living (abiotic) components. These two parts do not stand-3iisolation, however, the biotic component requires abiotic components. Actually, many minerals are continuously moving from abiotic world to biotic world and again back to abiotic world. Living organisms are also continuously modifying their surrounding non-living environment, and as we shall see later, help the process of . Interdependence of organisms (within themselves) and on abiotic world can be studied by carefully observing the plants and animals around your place. Look, for example, how nodules on the roots of legumes harbor bacteria which 'fix' nitrogen for the plant. See how the type soil and moisture content decide what kindof vegetation can grow in a particular area. Ecosystem is thus, essentially a biotic in continuous interaction with its physical environment. It is a dynamic entity. Taking a large, aslronautical view, the entire biosphere can be seen as a gigantic single ecosystem. We will actually see later that some materials like water, carbon dioxide, etc., are circulated globally. By biosphere we mean that portion of the earth and its atmosphere which supports life. All the different ecosystems that we mentioned earlier are then parts of the biosphere. Later, we will be analysing some of these ecosystems in details to have a look at their abiotic and biotic components. Let us fast study some basics about these two components. 10.3.1 The Biotic Component The biotic component is, of course, all the living organisms present in an ecosystem. Some of these organisms are large while some are tiny. Considerable number of organisms are so 'midute that these cannot be seen with a naked eye. So bacteria, fungi, small algae and plants, shrubs and trees, insects and birds, all are parts of the biotic component. Man is also a part of this vastassemblage of organism He is the only organism, however, who can modify vast areas of his environment within very short time. Apart from the strength of his Ecosystem :Basic Concepts muscles, he alone can make tools and machines and use them Biotic component is further subdivided into two broad groups on the basis of their trophic (nutritional) status. These groups are : 1) Autotrophic organisms which, as their name implies, are 'self nourishing' organism~, In short, these organisms can produce their own food. These organisms are generally, ' chlorophyll possessing plants, though of course, other pigments are also useful. Thus, all green plants mainly are and since they use solar energy they are also called as photoautotrophs. Some bacteria can survive on the energy generated through chemical reactions alone and are known as chemoautotrophs. 2) Heterotrophic organisms which, as their name indicates, are 'other-nourishing'. This means they depend on others for nourishment as they cannot prepare their own food. You can also call autotrophic organisms as producers because they produce food. Similarly, heterotrophs can also be identified as consumers as they consume food generated by the producers. Once again all plants are producers and all animals (and other organisms that do not manufacture their own food) are consumers. Sometimes the consumers are grouped into two - (a) macro-consumers, and (b) micro-consumers. The former includes all animals while the latter category includes bacteria and fungi that decompose organic matter produced by living organisms as well as remains of dead organisms. To introduce yet anotber terminology, we can call the organisms that feed directly on plants as , while those that feed on animal flesh as . What is important to note is that the biotic component of an ecosystem always consists of producers and consumers or autotrophs and heterotrophs. Each ecosystem will, of course, be different. Each will have its own producers and consumers. No two ecosystems will ever be absolutely similar as far as their biotic component is concerned. Each has'a unique composition. For example, a pond will have algae and other aquatic plants as producers whilei grassland has various grasses and shrubs as producers. 10.3.2 Abiotic Component The abiotic component of an ecosystem is everything else other than the living organisms.'~( is an assemblage of organic and inorganic substances present in an ecosystem. The various : climatic factors that affect the ecosystem functioning are also included in the abiotic component. Once again you will note that each ecosystem is unique in possessing a set of different abiotic factors. Substances like water, arbo on dioxide, phosphates, carbonates, nitrates, etc. and elements like carbon, nitrogen gas, sulphur, phosphorus, etc, are found in the ecosystems.These are called as inorganic substances. There are also simple and complex organic substances, for example, amino acids, humic acid, acetates, etc. These inorganic and organic substances may be present in such a form that organisms can utilize them. Some substances, however, may be cqinplexed or bound with other substances and may not be easily available to living, oiganismk. In any case, life of all the living organisms depends upon presence of these abiotic substances. After all, these substances are the building materials with which living organisms construct their structures. As we shall see later in this unit, the inorganic elements are constantly circulating between the biotic and abiotic compartments of the ecosystem. You exhale carbon dioxide and plants take it up to fix the carbon into a sugar molecule. When this sugar molecule is oxidized, once again carbon dioxide is produced, You will also study the various biogeochemical cycles to remember this point permanently. Climatic factors are also considered under the abiotic component because they control the entire functioning of an ecosystem, what kind of ecosystem can develop is largely determined by the climatic factors. Major changes in the climate are not routine features. Usually, climate change takes place gradually over a prolonged period and the ecosystems undergo modification. As we will see in other unit, even catastrophic climatic changes , brought about by volcanic eruption alter the ecosystem. In the distant past the continents; as' we see them today, occupied diffemnt positions on the surface of the earth. North America for example, was near equator and had tropical climate. The ecosystems present then were of course tropical but today the situation is entirely different. Biotic components also affect abiotic &mponents. For example, presence of vegetation alters t& soil and prevent its erosion, The ecosystem as a whole is an interplay or interaction between the abiotlq and biotic components.

7 S,P!Q :I a) Define ecoltrgy. tp) Detine atnBc~~Bogyaad sy~heh;oBogy. C) I~ekj~4~itlg icr~~??; ;!I sb0t~oi3i1i~ ILFI~ la.;tei17ks.opRaic c~rgCmisn~s. d) PIQsal ;irz biotic ai~dsbdoUc coanpoe:eats of sans ecosystcn~:I

10.4 FUNCTIONS OF AN ECOSYSTEM Let us now see how an ecosystem functions, how plants and animals are related with each other through food-chain, how energy passes from one organism to the other and how the minerals circulate between the biotic and abiotic component of an ecosystem 10.4.1 Food-Chain and Food-Web You might have seen a grasshopper nibbling at a plant or an insect larva feeding on the leaves of a plant. Further, you might have also noticed a bird feeding on grasshopper or insect larva. What you have observed here is a simple food-chain. Since no animal can manufacture its own food it will either directly feed on plant or will eat another animal and may, in turn, be eaten by yet another animal. This linkage of organisms for the transler of food energy is what we call as a food-chain. Basically, there are two types of food-chains : a) the grazing food-chain, and b) the food-chain. The grazing food-chain starts with a green plant which will be eaten by a plant eating animal (that is ). The herbivore, in turn, will be eaten by a flesh eating animal (that is ). Thus, simply stated the of this type can be : Plant -Herbivore ------+ Carnivore (Grass) (Insect) (Lizard or Frog or Bird) The detritus food-chain begins with organic matter from &ad organisms, etc. This organic matter is degraded by microorganisms (that is ). Thus, dead leaves, stems and such parts of plants or dead animals or their organic wastes will be degraded. Thus, it can be shown as : Dead log of wood ----c Wood rotting fungi

The important thing about the detritus food-chain is that the activity of microorganisms I release important inorganic nutrients that can be once again useful for other organisms. Had it not been for detritivores, a lot of energy would have remained locked up in the dead I bodies of organisms (Figure 10.1 (a)). In most ecosystems, the food chains are not so simple and straightforward. An insect like grasshopper may feed on a dozen different plants. Similarly, a frog may eat several other insects along with grasshopper. Thus, the food-chains are not simple isolated sequences as discussed above. Rather there is considerable interlocking of food-chains. We then speak of a food-web rather than a foodshain while studying an ecosystem This is because even a single animal, during its development and growth, may be a pkt of a different food-chain and hence a food-web. A simple food-chain in a small lake is shown ih Figure 10.1 (b). Ecosystem : Bwic Concepts

GRAZING CARNIVORES TYPE OF FOOD CHAIN

DETRITUS TYPE OF k FOOD CHAIN MINERALIZATION BACTERIA, FUNGI, PROZOANS

(u) Grazing and Detritus Type of Food-chnins nnd their lnterrclntionship

SMALL FISH

. . DETRITUS

(I))A Sin~plelcood-cbnin 111 11 Smnll Lnkc Ipigurc 10.1

10.4.2 Trophic Levels We have seen that each ecosystem has complex food-webs. However, in a food-chain the organisms, where food is obtained from plants by the siune number of steps, are said to belong to the same . In our food-chains, namely : a) grass ------grasshopper frog - snake and b) tree - beetle -.---+ lizard ---- bird the grasshopper and beetle both occupy the same trophic level. Both are directly using plant as food and are called as primary consumers. The plants, that is, the grass and the tree both are at the producer level. Likewise, the first animal eaters, that is the frog and the lizard occupy a level called as secondary consumer level. Similarly, there is a tertiary consumer level. Thus, the trophic levels can be stated as : Producer- Primary consumer -+ Secondary consumer- Tertiary consumer But please note that this is not a trophic classification. It tells us about the function of a species in question. It is also important to remember that one animal may occupy One or more than one trophic level. This complexity is also evident from the food-web. 10.4.3 Energy, Sources of Energy and Energy Flow Physicists define energy as the ability or capacity to do work. Work can mean movement, hands or legs, growth, movement of a car, etc. Virtually all actions of living things reqJre energy. Muscles do not contract without energy, so you cannot move any part of body without spending some amount of energy. Not only that, many other reactions going on in your body (for example movement of cellular constituents, synthesis of cellular proteins a carbohydrates, ctc.) also require energy. At all levels of biological organization, there ex; processes that channel energy into the various activities and that this channeling is admirably well controlled. For this reason it is said that all living systetns, from single cell to a complex community, are energy convertcrs more than anything else. Energy can be divided into two basic forms : I) potential energy and 2) kinetic energy. Potential energy is simply stored energy which is available to do work. The living cells generally store potential energy in the form of high energy phosphate bonds. When these bonds are broken the liberated energy can be used to do work. The most common 'energy rich' compound used by #e cell is adenosine triphosphate or ATP. The other similar compounds are uridine triphosphate (UTP) or guanosine triphosphate (GTP), etc. The common reaction is :

where 'ATJ?' is a diphosphate, 'P,' is inorganic phosphatc and 'e' is energy. This reaction reversible. Although it is beyond the scope of this course, you must know that all animals generate their own ATP but the energy required to do so comes lrom food they eat (vegetable or flesh). All we do is break down the sugar or proteins or Pdts and obtain the potential energy trapped in those molecules. Kinetic energy on the other h&d is associated with movement. Water falling down a watej fall (this is how we run ow turbines to generate electricity at hydroelectric station), blowin wind, the waves pounding on a sea shore or a moving car. All are examples olkinetic energy. There are other forms of energy, like atomic energy, geothermal energy, solar energy or radiant energy which is in the formof electromagnetic waves, and .also heat. As we remarked earlier all consumers depend ultimately on solar energy. The production c a (and hence availability of plant and animal resources) in a given ecosystem is determined primarily by solar radiation. Mean intensity of solar radialion is the most important factor. As far as the flow of energy in an ecosystem is concerned, it directly depends on the amount of solar energy captured per unit area in unit time by the plants. In the presence of sunlight the chlorophyll (the green pigment) containing plants are capab of fixing carbon dioxide to form sugar. Thus

light energy 6 CO, + 6 H,O *C,H120, + 60, (carbon dioxide) (water) (sugar) (oxygen) nere are also pigments other than chlorophyll which can also do the same thing. This process is . The amount of solar energy falling on earth is variable according to season, latitude, cloud cover and such other factors. Much of this energy is wasted and ends up in heating the eartl and its atmosphere or is reflected back from earth. Only a tiny fraction of incident solar energy is fixed by the plants to prepare their food (sugar). The amount of plant biomass developed per unit time per unit area is sometimes known as gross . Plants of course use some food for their metabolism (respiration) and the remaining biomass is then the net productivity. The energy present in the plants is then used by the subsequent members of the food-chain. This entire movement and overall behaviour of energy obeys the laws of therxnodynamics. Let us briefly see those two laws and their implications in ecology. The first law of thermodynamics explains that energy can neither be created nor destroyed it is merely transformed, that is it changes its fonn. The plants transform solar energy (radiant energy) into potential energy by using the sunlight to produce sugar from carbon dioxide. When an animal eats the plant or animal material as food, the same energy is gradually liberated in the process of respiration to produce the energy rich phosphate molecules. This we have discussed earlier. It is in this sense that the ecologists say that all living organisms are merely energy converters. The second law of thermodynamics points out to us tllat no process of transformation of energy is possible without partial degradation of energy. By degradation we mean conversion of concentrated and orderly form of energy into a 'dilute', unusable form. This means there is a loss of useful energy. Please remember cnergy is not lost or destroyed, simply it is in a form that is not serving our purpose. The most important ecological implication of this law is that no biological process can take place with 100% efficiency. Already we have seen that much of the solar energy incident on plant is not fixed. Further when an herbivore feeds on this plat11 again some energy is lost, this continues along the food-chain. Obviously the nature cantlot dford to have too long food-chains. This is the reason why a unit area of land can feed more vegetarian people lhan if the s'ame area is used to grow grass on which meat-providing ani~nalsa~c: grown and then tlle meat is pr0vided.a~ a food to people. Energy also moves only oncc through any given trophic level of Ule food-chain (Figure 10.2). As we shall see the ininera1 nlaller is used and reuscd in cyclic manner Energy is gradually degraded along the food-chain 'and finally dispersed as heal.

ORGANIC MATTER WASTES AND DEAD BODIES

Agurc 10.2 : line Diagran~Slrowitrg One-way I'wsrrgc of Pllergy from Plir~iCFto Herbivores to C~uluvorcsrrnrl I?itl:~llylo Dccomposcrs SAQ 2 a) Explain the cc~lccptof footi-chain with a suit;lblc cxample. b) llefinc gr;rzing aritl rlctritus t'cn)tl-chains. c) What is a food-web '! d) Statc two laws ol' tberlllodyniklllics. e) Dci'inc potoiitiiil c~lol'gy;ultl ki~lcliccnergy.

10.4.4 Biogeochemical Cycles The chemical elements especially the essenlial six elements are required by living organisms in large quantity. lllese are carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Some other elements such as sodium, potassium, muig,mese, calcium, iron, magnesium, chlorine, iodine, elc. arc required in smaller quantities. All tllese elements are < pfesent mainly in the earth's crust. Gases like oxygen and nilrogen are present in atmosphere. These chemical elements tend to circulale in the biosphere in characteristic I paths from environment to organisms and back to the environment. nese more or less circular paths are known as biogeochemical cycles. Ille inorganic compounds essenlial for the growth of life follow what are described as nutrient cycles. For each cycle there is a reservoir pool. This is usually largc, slow-moving and generally non-biological component. The otl~ercomponent of the same cycle is exchange pool or cycling pool, which is smaller but more active portion that is exchanging rapidly between organisms and their immediate environment.

A Ecology These biogeochernical cycles can be broadly divided into two types. One, gaseous type in which reservoir is almosphere and second, sedimentary type in which reservoir is l.Ile earth's crust. We can describe nitrogen cycle as an example to tell you how there is exchange of material from abiotic to biotic and biotic to abiotic componenls of ui ecosystem. Herc nitrogcn in Ule air serves as reservoir pool and this nitrogen is fixed by certain planls with the help of micro-organisms and by electrification process in nature. As an output, nitrogen is fixed from atmosphere and then ~t is used again and again through various biological processes. This is how nature uses its resources efficiently.

1- 1- NITROGEN IN ATMOSPHERE -7

ELECTRIFICATION & NITROGEN FIXING PHOTOCHEMICAL BACTERIA 8 AL6AE FIXATION I 1 /, DENITRIFICATION

4 NITRATES NITRATES fl

PROTEIN SYNTHESIS PLANTS -4 ANIMALS BACTERIA \

EXCRETION, DECAYING PARTS OF WASTE PRODUCTS PLANTS h ANIMALS BY THE OF ANIMALS ACTION OF BACTERIA h FUNGI

4 NITRITE

Figure 10.3 : Nitrogen Cycle This is also true for other cycles such as phosphorus, O,, CO,, elc. Now, we can lean other cycles with the help of a few diagrams : 1) Phosphorus cycle (also known as sedimenlary cycle) 2) Carbon Cycle

Figure 10.4 I Pl~osjihorusCycle :I Ecosystem : Bmic Concepts C02 IN THE ATMOSPHERE 1 1 I 1 1

PHOTOSYNTHESIS .

IGNEOUS ROCKS NATURAL PROCESSES DETRPIZTS WSD

OCEAN

Figure 10.5 : Carbon Cycle

10.5 THE CONCEPT OF HABITAT AND ECOLOGICAL NICHE The term habitat is often used in ecology to denote the 'address' of an organism. It refers to Ihe place where that organisms lives. When we say that a particular fish is found in the hill streams, the hill stream is the habitat of that fish. But two different species of hill stream fishes may occupy different areas within such streams. Such areas or preferred areas then become microhabitat for Lhat particular species. Thus the microhabitat for one fish may be shallow hill stream rocks covered with algae. So when we clearly define the habitat of a species we also include abiotic and biotic environment that surrounds an organisms. Each organism is adapted to a specitlc habitat and any modification of the habitat can be dangerous for survival of that organisms. Told destruction of a particular type of'habilat can wipe out an organism from th,at area. In fact many plants and animals became extinct due to habitat destruction carried out by the industrialized and urbanized human being. When we convert a jungle into a pasture land or agricultural land we are deskoying of hundreds of species. The term ecological niche is more broader tcrm. It speaks about : (a) the physical space occupied by an organism, (b) functional role of a given organism in a community, and (c) heposition of that organism in the environmental gradients (say, of temperature, salinity, etc.). The same three aspects of ecological niche are sometimes known as spatial or habitat niche, trophic nic11e.and ~nultidimensionalniche. Certainly, ecological niche tells us many more U~ingsabout the organism, especially with respect to its role in a given community. Understanding niche is essential to distinguish differences betwcen similar species, For example, three or more species of closely related birds may be occupying the same area yet each one feeds on different food and each nests in different tree. We will further discuss about ecological niche again in Unit 11.

L 10.6 THE CONCEPT OF HOMEOSTASIS Living systems, including groups of organisms living together in the same environment as well as individual organisms, possess self-regulating feedback mechanisms Ulat maintain their equilibrium. This tendency of biological systems to resist change and remain in a state of steady equilibrium is called homeostasis. The roots of this word are : horne.0 = same and slasis = tand ding. Regulation of body temperature or blood-sugar level is an example of homeostatic control al Ule individual level. To maintain population density is similar control at the level. Maintenance of overall structure of an ecosystem constant over a period of time is also homeostasis. Homeostatic control needs information in the form of feedback. Feedback is simply return of the output (or part of the output) to a system as input. This feedback gives information whether the system should continue to function along the same line or alter its course. It must be pointed out however that it takes a lot of time to understand such controlling signals at an ecosystem level. As E.P. Odum bas rightly pointed out, man is disrupting the equilibrium of many ecosystems by disrupting the controls. At this point of time a careful investigation of all the ecosystems that surround all of us is necessary. This will allow us to get the benefit out of an ecosystem at the same, keep the ecosystemfunctioning. You must also remember that homeostatic control observed in any ecosystem is the result of prolonged evolutionary adjustment. As we shall see later, when we discuss ecological succession, the older and mature systems are more at equilibrium than the new sera1 communities.

10.7 TYPES OF ECOSYSTEMS Over this p1,anet earth there are several types of ecosystems. Broadly, we can divide them into two types : a) terrestrial and b) aquatic ecosystems. This is a habitat wise classification. There are again several different terrestrial ecosystems in different parts of the earth. The various forests, grasslands and savannas, deserts, etc. are all terrestrial ecosystems aboul which we shall discuss later. Similarly, freshwaterecosystems and marine ecosystems of different category are classified under . What kind of ecosystem can develop at any particular place depends on several factors. Among these factors, the amount and duration of sunlight, availability of water, the type of soil and other geological factors and overall climate are very important. We will be discussing some of these things later in this block.

a) What is meant by biogeocherPlical cycles ? Represent my one cycle diagnmmatically. b) Explain the concept of'ecologicd niche. c) Explain the concept of homeostasis.

- 10.8 SUMMARY In this unit you have noted some basic concepts in ecology. We have defined ecology as tlle science dealing with the study of the structure and fu~ictionof an ecosystem. The ecosystem itself is a structural and functional unit of ecology. Many ecosystems together form the biosphere. The ecologist may concern himself with single organism (autecology) or with groups of

organisms in an ecosystem (synecology). I Each ecosystem, you must note, has a living (bioti~)and a non-living (abiotic) components. These two components are continuously exchanging materials with each other. This is what we have discussed as biogeochemical cycles. ~achecosystem also has a definite trophic structure and you can speak about the trophic status of each organism. The plants which manufacture food are called as producers while all the rest organisms are consumers. You have observed that the food energy present in I plants passes down to acamivorous animal through an intermediate herbivorous animal. This passage of food cnergy along definite line of organisms is the food-chain. The food-chain itself being part of a greater and complex food-web. The main source of energy is, of course, solar energy and the behaviour of energy in an ecosystem follows the laws of I thermodynamics, You have also noted that each ecosystem tries to maintain an equilibrium. There are specific

feedback signals that help the ecosystem to maintain equilibrium. I I Ln the end, you must also remember that different kinds of ecosystenls arc found in different Ecosystem :Basic Concepts parts of the world. The amount of solar radiation is one of the main feature deciding what kind of ecosystem can develop at a given location, of course availability of water, soil, etc. are also factors to be considered. We must not forget that man is also a part of the ecosystem and hence his well-being is dependent on well-being of the ecosystem. He should not allow the ecosystems to degrade and modify due to his activities.

10.9 KEY WORDS A biotic All non-living components of an ecosystem. Aerobic Refers to the biological processes taking place in presence of oxygen. Algal bloom Excessive growth or proliferation of one or few species of algae in water bodies giving greenish colour to water is called algal blooms. Tlnese algal blooms are caused due to input of excessive plant nutrients e.g. nitrogen and phosphates through domestic wastelsewage 'and leaching of fertilizers from agriculture. Anaerobic Tlne biological processes which take place in Une absence of air are known as lulaerobic. Aquatic The plant and a~imillspccics living in water are called as aquatic species. Assimilation In ecology it refers to tlne conversion ol' hod material into substance of cell or an organism. Autecology This is a branch of ecology in which a single species of plant or a~i~nalis studied. Autotrophic Auto rncans self ;md lrophic mexns food i.e. self-feeding. This term refers to the green plants which by tlne process of photosynthesis manuhctures Uneir own food utilising CO,, water iund energy of sunlight. Bacteria Tlnis is a group ol micro-orgiunisnns popu1;irly fanliliar by their disease causing ability. Many bacteria are essential in rnaturc for recycling ol'matcrials and they play important role in an ecosystem. Benthos Plants and animal species living on the bottom ol' water bodies for exarnplc organisms living on or near bottom of an aquatic body. The term bio-assay refers to he use of living organisms or their tissues to rncasure the biological effccts of ~nan-madeandlor natural substances. The substances which can be reduced to smaller components or milleralized by ~nicroorgimismsare called as bio-degradable. Plastic material may nol be degraded by micro-organisms and is called non-biodegradable. : The clnenlicals esscntial for organisms are circulated in the nature in a cyclic rnarlner froin physical environment (abiotic) to organisms (biotic) and back to environment in the form of waste, death of organisms, etc. This cyclic movement of matter is called as biogeoclnernical cycles. Biological oxidation : Degradationloxidation of organic material with the help of organism. This helps in recycling of material in an ecosystem. Niche Functional status of an organism in a community. Habitat Place of an organism where it lives, Ecology 10.10 FURTHER READINGS Kurnar, H.D.(1995), General Ecology, Vikas Publishing House, New Delhi. Other books mentioned in the next unit.

-- 10.11 ANSWERS TO SAQs SAQ 1 a) Ecology is the study of relationship of an organism or groups of organisms to their environment. It is actually the study of the structure and function of nature. b) Autecology i$ the ecology of single organism, plant or animal, while the term synecology denotes study of groups of organisms which as associated together as a unit. c) Autotrophic organisms are self-nourishing organisms that is, those that manufacture their own food. All plants (with few exceptions) are autotrophs. The heterotrophic organisms on the other hand depend on olher organisms for food as they cannot produce their own food. . d) Biotic and abiotic components are constituent parts of ecosystem. Biotic component includes all living organisms (from bacteria to elephant) while the abiotic components are all non-living things (soil, gases, climatic factors, etc.). These two components continuously exchange matter through biogeochemical cycles. SAQ 2 a) When a portion of plant is eaten by a grasshopper and the grasshopper is in turn eaten by a frog then energy stored in plant passes through grasshopper to frog. This transfer of food energy from its source in plants through a series of animals is called as the food-chain. Thus we can show it as : Grass leaves ------c Grasshopper -Frog b) The food-chain which starts from a green plant and passes through herbivorous animals to carnivorous animals is the grazing food-chain. The food-chain which originates from dead and decaying organisms or organic wastes is called as the detritus food-chain. c) Though we have seen that Grass leaves -Grasshopper -Frog is a food-chain, the picture is not always like that. The grass leaves will be eaten not only by grasshopper but also by rabbits and similar other mammals. Similarly, a grasshopper may be eaten by a Lizard, by a bird even by a young one of snake. We must also note that there are several kinds of grasses, grasshoppers, frogs, snakes, rabbits, etc. so the interrelationship is quite complex. This interlocking nature of the food-chains is known as the food-web. d) The first law of thermodynamics states that energy can neither be crealed nor destroyed. It can be however, converted (transformed) from one form into another. The second law states that with each such transformation there is loss of "useful" energy. That is it often passes from its concentrated and orderly state to more dispersed (hence useless from our point of view) state. e) Potential energy is the energy stored in various molecules like sugar. This energy is available to do work when the sugar molecule is broken down, Kinetic energy on the other hand, is energy associated with movement. SAQ 3 a) Cyclic movement of mineral matter between biotic and abiotic components of an ecosystem is a biogeochernical cycle. It can be shown as : I abiotic component C biotic component I Different minerals follow different path, so is the case with the gases like Ecosystem : 13;lsic Concepts nitrogen, oxygen. b) Each organism of an ecosystem has a definite function, a definite role to play. This functional status of an organism is called as ecoIogical niche. The function of an organism can be analyzed only when we how more about the place where the organism lives (spatial niche), the energy sources, etc, of an organism (trophic niche) and environmental gradient (say, of temperature) in which it lives (multidimensional niche). The all encompassing concept is that of ecological niche which includes all the aspects discussed above. c) Homeostasis is the tendency of an ecosystem to maintain equilibrium and resist changes (Homeo = same, Stasis = standing). External agents are constantly disturbing the equilibrium yet as soon as is over the system remsto nonnal. This is possible due to various feedback control I signals that operate to maintain equilibrium. Such controls are at the individual, population and ecosystem level. Maintenance of constant blood sugar level or maintenance of right body temperature are examples of homeostasis. Regulation of prey population by a predator is an example at the ecosystem level.