BEVAE-181 Environmental Studies PDF

 BEVAE-181 Indira Gandhi National ABILITY ENHANCEMENT Open University School of Sciences COMPULSORY COURSE ON ENVIRONMENTAL STUDIES BLOCK 1 An Introduction to Environment and Environme...

 BEVAE-181 Indira Gandhi National ABILITY ENHANCEMENT Open University School of Sciences COMPULSORY COURSE ON ENVIRONMENTAL STUDIES BLOCK 1 An Introduction to Environment and Environmental Studies 5 BLOCK 2 Natural Resources 63 BLOCK 3 Environmental Issues and Concerns 147 BLOCK 4 Protecting Our Environment: Policies and Practices 225 Glossary 291 Course Design Committee Prof. M. S. Nathawat Prof. B.I. Fozdar Prof. Bano Saidullah School of Sciences, School of Sciences School of Sciences IGNOU, New Delhi IGNOU, New Delhi IGNOU, New Delhi Prof. Vijayshri Prof. Neera Kapoor Prof. Subhakanta Mohapatra School of Sciences School of Sciences School of Sciences IGNOU, New Delhi IGNOU, New Delhi IGNOU, New Delhi Prof. Sunita Malhotra Prof. Amrita Nigam School of Sciences School of Sciences IGNOU, New Delhi IGNOU, New Delhi Block Preparation Team Prof. Subhakanta Mohapatra (Unit 1 and 5) Content Editor Prof. Bano Saidullah (Unit 2) Prof. A. K. Bhatnagar Retd. Prof. in Botany Prof. Amrita Nigam (Unit 3, 6 and 8) University of Delhi, Delhi Prof. S. S. Hasan (Unit 4, 7, 9, 10, 13 and 14) Prof. Neera Kapoor (Unit 6 and 8) Prof. Sunita Malhotra (Unit 11) Prof. B. I. Fozdar (Unit 12) Course Coordinator : Prof. Subhakanta Mohapatra Print Production Sh.Rajiv Girdhar Sh. Sunil Kumar Sh. Hemant Kumar Parida Assistant Registrar (Pub.) Assistant Registrar (Pub.) Section Officer (Pub.) IGNOU, New Delhi IGNOU, New Delhi IGNOU, New Delhi Acknowledgement: Mr. Siddhant Mahapatra for designing cover page, Mr. Rohit Kumar, Ph. D. Scholar, SOS for preparation of Fig. 4.14, 6.2 and 13.2 and Mr. Anil Kumar for assistance in word processing and graphic work. September, 2019 © Indira Gandhi National Open University, 2019 ISBN: 978-93-89499-79-7 Disclaimer: Any materials adapted from web-based resources in this module are being used for educational purposes only and not for commercial purposes. All rights reserved. No part of this work may be reproduced in any form, by mimeograph or any other means, without permission in writing from the Copyright holder. Further information on the Indira Gandhi National Open University courses may be obtained from the University’s office at Maidan Garhi, New Delhi-110 068 or the official website of IGNOU at www.ignou.ac.in. Printed and published on behalf of Indira Gandhi National Open University, New Delhi by Prof. Poornima Mital, Director, SOS, IGNOU. Laser Typeset by : Rajshree Computers, V-166A, Bhagwati Vihar (Near Sector 2, Dwarka), Uttam Nagar, New Delhi-110059 Printed at: Nutan Printers, F-89/12, Okhla Industrial Area, Phase-1, New Delhi - 110020  COURSE INTRODUCTION Earth is the only known planet in the solar system that supports life. Despite the vastness of the Earth, life exists only in a very thin layer of the Earth called biosphere. For a long period of time, there has been a symbiotic relationship between human being and nature. Due to excessive human interference and unsustainable practices, millions of people’s life and livelihoods are at risk. Therefore, there has been a growing need to create awareness amongst all the stakeholders. Keeping this in view, Environmental Studies is being introduced as a compulsory course for all the learners at under-Graduate level. This course has four blocks. Block 1 An Introduction to Environment and Environmental Studies: Today, human society is standing at a cross road and searching for the better alternatives for sustainable future earth. That is why there is a necessity that every individual should have awareness and knowledge about the earth’s environmental resources, human-environment relationship and issues emerging out of human-environment relationship. This block has made an attempt to establish the importance of symbiotic relationship and the need for sustainable development. This block consists of three units. Unit 1 introduces concept of environment and nature and importance of environmental studies. Unit 2 discusses about the concept, features, types and functions of ecosystem and Unit 3 describes about major ecosystems on the earth. Block 2 Natural Resources: This block discusses about natural resources that provide the base for human sustenance and development by providing ecosystem services. There has been substantial decline and degradation of natural resources over the years. As a result of which, there has been a negative impact on ecosystem services. Therefore, there is a need for sustainable natural resource management. This block consists of four units. Unit 4 deals with land and water resources while Unit 5 discuses about forest resources. Biodiversity: Values and services are discussed in Unit 6 and energy resources were explained in Unit 7. In all these units, resources are discussed in terms of distribution, availability, utilisation, causes of degradation and need for and methods of conservation. Block 3 Environmental Issues and Concerns: This block consists of four units related to various environmental issues confronted by humans at different levels - local to global. Unit 8 titled Biodiversity: Threats and Concerns focused on causes of bio-diversity loss and measures for biodiversity conservation. Unit 9 ‘‘Environmental Pollution and Hazards’’ discussed about the phenomenon of pollution in air, water and soil, their sources and their effects. Apart from these, noise, radiations and thermal pollution have also been discussed. Unit 10 titled Waste Management discussed about the waste and various ways of waste disposal system which have minimum harm to the environment. Unit 11 titled Global Environmental Issues discussed the causes and effects of phenomena namely, global warming, acid rain, ozone depletion and some of the measures taken to deal with these issues. Block 4 Protecting Our Environment: Policies and Practices: This block being the last block of the course has attempted to address the policies, beliefs and practices associated with environment. This block consists of three units. Unit 12 deals with environmental legislation whereas environmental ethics are discussed in Unit 14. Unit 13 covers issues related to human communities and environment. BEVAE-181 ABILITY ENHANCEMENT COMPULSORY COURSE ON ENVIRONMENTAL STUDIES Block 1 An Introduction to Environment and Environmental Studies Unit 1 Our Environment Unit 2 Ecosystems Unit 3 Major Ecosystems Block 2 Natural Resources Unit 4 Land and Water Resources Unit 5 Forest Resources Unit 6 Biodiversity: Values and Services Unit 7 Energy Resources Block 3 Environmental Issues and Concerns Unit 8 Biodiversity: Threats and Conservation Unit 9 Environmental Pollution and Hazards Unit 10 Waste Management Unit 11 Global Environmental Issues Block 4 Protecting Our Environment: Policies and Practices Unit 12 Environmental Legislation Unit 13 Human Communities and Environment Unit 14 Environmental Ethics  BEVAE-181 Indira Gandhi National ABILITY ENHANCEMENT Open University School of Sciences COMPULSORY COURSE ON ENVIRONMENTAL STUDIES Block 1 AN INTRODUCTION TO ENVIRONMENT AND ENVIRONMENTAL STUDIES UNIT 1 Our Environment 7 UNIT 2 Ecosystems 21 UNIT 3 Major Ecosystems 45  BLOCK 1: INTRODUCTION Earth is the only known planet in the solar system that supports life. Despite the vastness of earth, life exists only in a very thin layer enveloping the earth called biosphere. Sun is the only source of energy which enables continuous interaction among various life forms. For a long period of time, there has been a symbiotic relationship between human being and nature but it is changing. Due to excessive human interference and unsustainable practices, millions of people’s life and livelihoods are at risk. Therefore, there has been a growing need to create awareness amongst all the stakeholders. Keeping this in view, Environmental Study is being introduced as a compulsory course for all the learners at under-Graduate level. This block consists of three units. Unit 1 introduces concept of environment and environmental studies. Unit 2 discusses about the concept of ecosystem and Unit 3 describes about major ecosystems. Unit 1 Our Environment: This unit, being the first in the course, brings out the holistic meaning of the word ‘environment’. This unit will also focus on how we as living beings interact with other living and non-living components of the ecosystem. For centuries humans have considered the earth and environment as an unlimited resource but subtle and gradual changes have altered our environment in many different ways. The concept of sustainable development provides an alternative model of development that could balance between environment and development. This unit will also discuss the multidiscipilinary nature and scope of environmental studies. Unit 2 Ecosystems: This unit deals with the structure and properties of ecosystem, basic concepts of ecosystem functioning, and the factors controlling it. It also deals with the development of ecosystem. The unit will also familiarise you with interactions like competition, parasitism and mutualism that exist between living beings. This unit will also focus on how we as living beings interact with other living and non-living components of the ecosystem and would also become aware that ecosystems are able to maintain homeostasis by active effort, resisting the tendencies toward disorder. Unit 3 Major Ecosystems: This unit discusses two broad categories namely terrestrial and aquatic ecosystems and their types. Major terrestrial ecosystems include forests, grasslands and deserts while lakes, rivers, oceans, estuaries and wetlands are collectively known as aquatic ecosystems. Besides, you will study about the importance of the forests, grasslands and aquatic ecosystems. We hope after studying this block, you will acquire an in-depth understanding of the physical components of the environment, the process related to them and their interactions with other components of the environment These units would enable you to use your intelligence and skills to the best of your advantage for managing our environment and keeping it healthy for future generations. Our best wishes are with you in this endeavour. Unit 1 Our Environment 1.......................................................................................................................................................................... UNIT OUR ENVIRONMENT Structure 1.1 Introduction 1.5 Concept of Sustainability and Expected Learning Outcomes Sustainable Development 1.2 Concept of Environment 1.6 Multidisciplinary Nature of the 1.3 Components and Types of Environmental Studies Environment 1.7 Importance of Environmental Studies Components of Environment 1.8 Summary Types of Environment 1.9 Terminal Questions Significance of the Environment for Life 1.10 Answers 1.4 Human-Environment Relationship 1.11 Further Reading 1.1 INTRODUCTION Earth is the only planet known for supporting life. Despite the vastness of earth, life exists only in a very narrow zone of the earth called biosphere. Sun is the only source of energy which enables continuous interaction among various life forms.This unit, being the first in the course, brings out the holistic meaning of the word ‘environment’. In broad terms, environment includes everything external to an organism that affects it, including physical as well as living factors. The action and interactionof the physical and living factors makes a system of relationships called ecosystem. This unit will also focus on how we as living beings interact with other living and non-living components of the ecosystem. The concept of sustainable development came into existence that explains symbiotic relationship between human being and environment. For centuries humans have considered the earth and environment as virtually unlimited resources but subtle and gradual changes have altered our environment in many different ways.Special mention has been made of human population within the changing scenario over the years, particularly since the industrial revolution. We hope that this unit will give you a better understanding of the environment and its various components. This unit would also enable you to use your intelligence and skills for managing our environment and keeping it healthy for future generations. This unit will further explain the multi-discipilinary nature and scope of environmental studies. Expected Learning Outcomes After completing the study of this unit you should be able to:  explain the importance of environment in our life and surroundings;  recognise the importance of the concept of sustainability and sustainable development;  analyse the multidisciplinary nature of environmental studies; and 7  appreciate the importance and scope of environmental studies. Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... 1.2 CONCEPT OF ENVIRONMENT Each and every living organism has a specific surrounding or medium with which it continuously interacts, derives its sustenance and to which it is fully adapted. This surrounding is the ‘natural environment’. The word ‘natural environment’ brings to mind broad aspects of landscape, such as soil, water, desert or mountains which can be more exactly described in terms of physical or abiotic influences such as differences in moisture, temperature, texture of soil, and air quality. It also includes the biological or biotic influences in the form of microbes and animals. Thus, environment is defined as, “the sum total of living and non-living components; influences and events surrounding an organism”. Let us begin by asking what is environment? Environment is derived from French word environ which means to encircle or surround while ment means auctioning, i.e., environment is the interaction between organism and the nature. For humans, there are several kinds of environment such as home environment, business environment, political environment and so on. But we are going to discuss only about natural environment: air, water, land, plants, animals and other organisms. Any individual in nature interacts with its environment, influences it and in turn is influenced by it. Thus environment is the sum total of air, water and land interrelationship among themselves and also with the human beings, plants, animals and other organisms. The most significant attribute of the effect of environment on life of an organism is the interaction of environmental elements. These abiotic and biotic factors are dynamic in nature and interact with each other in every moment of life. No organism can live alone without interacting with other organisms, so each organism has other organisms as a part of its environment. You must be aware that all animals are directly or indirectly dependent upon plants, basically the green plants that manufacture their own food. Plants also depend on animals for a few things such as pollination of flowers and dispersal of fruits and seeds. Let us try to understand the concept of environment with an example (Refer Fig.1.1.). Can you identify the environment of a carp fish in the pond? Its environment consists of abiotic components such as light, temperature, and water in which nutrients, oxygen, other gases and organic matter are dissolved. The biotic environment consists of microscopic organisms called planktons as well as aquatic plants and animals and decomposers. The plants are of different kinds such as floating, submerged and partly submerged plants, and trees growing around the edge of the pond. The animals consist of insects, worms, molluscs, tadpoles, frogs, birds and various kinds of fishes.The decomposers are the saprotrophs like bacteria and fungi. 8 Unit 1 Our Environment.......................................................................................................................................................................... Fig. 1.1: Environment of a Carp in a Pond. Till now, you might have realised that the environment is not static. The biotic and abiotic factors are in a flux and keep changing continuously. The organisms can tolerate changes in environment within a certain range called ‘range of tolerance’. 1.3 COMPONENTS AND TYPES OF ENVIRONMENT After discussing about the concept of environment. In this section, we will discuss about components, types and significance of environment. 1.3.1 Components of Environment Broadly the environment comprises of abiotic (non-living) and biotic (living) components. Some examples of abiotic and biotic components of environment are listed below in Table 1.1 Table 1.1: Components of Environment Abiotic Components Biotic components Light Plants Precipitation Animals including humans, parasites and micro Humidity and Water organisms Temperature Decomposers Atmospheric gases Seasonal changes Topography The physical components set the condition for the survival of the biotic components, which in turn take care of the maintenance of the environment. Linkages among components of the environment are pathways for the flow of energy and cycling of materials. For example, green plants obtain essential resources from the physical realm – water and minerals from the soil, carbon dioxide from the atmosphere and light energy from the sun, and manufacture their food. Animals depend on plants and other animals for their source of 9 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... food. We, the human being, in turn harvest the land and the seas for our food; and obtain minerals and fuel from the Earth’s crust. We will learn more about these later in this course. 1.3.2 Types of Environment Recall the definition of the environment, and consider a fish living in a natural pond which we have already discussed in the previous section. Its external environment will be the water in the pond which it primarily inhabits. The water would contain nutrients, oxygen and other organisms that the fish requires to sustain its life. As opposed to the external environment, the body cavity within the fish provides an internal environment quite separate from the outside environment. The body surface act as an exchange barrier between the internal and the external environment of the fish. The internal environment is relatively stable as compared to the external environment. However, illness and injury or even environment stress can upset it. But when the cause of the disturbance is removed, the internal environment comes back to its original condition. The pond which the fish inhabits is its natural environment. The abiotic factors of the pond, like light, temperature, depth, nutrients, and dissolved gases will provide the life supporting chemical and physical factors for the fish. The other living organisms inhabiting the pond, like bacteria, insects, worms, molluscs, tadpoles, frogs and aquatic vegetation could be food for the fish. Examples of such natural environments on land include forests, grasslands, savannah and deserts. So far we have discussed only the natural environment but there are several components of environment which are created by humans, like crop fields, cities and industrial spaces (Fig. 1.2). These are places made artificially by humans through planned manipulation. For Natural Environment Oceans, lakes/ponds, rivers, forest, grasslands, deserts etc. Human-modified Environment Orchards, plantations, sanctuaries, parks, etc. Human-made Environment Industries, cities, towns, crop fields, artificial lakes, dams, etc. Fig. 1.2: Examples of Different Types of Environment. 10 Unit 1 Our Environment.......................................................................................................................................................................... example, let us consider a city. The city environment is totally created by human beings. One of the most important components – water is not taken from streams directly but is first filtered, purified and then used for drinking and other municipal purposes. The metabolic waste and garbage are not disposed off locally but are carried for treatment or dumping to a remote place, away from the city. Food for the people in cities often comes from rural areas. An environment made by humans results in the consumption of excessive amounts of materials and energy, necessitating care, supervision and management. 1.3.3 Significance of the Environment for Life Whatever type of environment organisms inhabit, they all need life supporting elements for their survival. These include air that they breathe, food and water they take in, and shelter either as natural (like caves and tree holes) or as artificial dwellings (like houses). Environment is the only source that provides these life supporting elements. We make use of the land for cultivating crops. Soil provides nutrients needed for the growth of plants. The landform determines the soil types found in any one area and soil itself varies from place to place. Some soils are rich in nutrients and other are lacking in them. The soils lacking nutrients need the addition of fertilizers.Climate and short term weather changes are characterized mainly by wind, temperature, pressure and rainfall and are determined by the properties of the atmosphere. Air in the atmosphere provides living organisms with oxygen, without which survival of the most of the living organisms will be threatened. SAQ 1 Answer the below given question within 30 words. i) Describe the significance of physical components in an environment. ii) Explain in brief the significance of the environment for life. 1.4 HUMAN - ENVIRONMENT RELATIONSHIP As we know from the previous section that all living beings are dependent upon their immediate surroundings for their sustenance and survival. There are two distinct situations observed if we trace the history of human civilization. The first situation is that human being adjusted or adapted to the prevailing environmental conditions. Those who could not adapt or adjust perished. Similar situations can be observed amongst plants and animals also. As human civilization progress, people developed knowledge, skill and technology to subjugate nature. This happened faster after renaissance and Industrial revolution. It has improved standard of living as well as made human life comfortable. However, this has leads to irreparable damage of environment and threat to the human society as well as survival of the planet earth. Therefore, it has been realized that there should be a balance between 11 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... development and protection of environment. This approach is best expressed as ‘sustainable development’ which we will discuss in detail in the next section. But now, let us consider the various approaches to human-environment relationship i.e. determinism, possibilism and environmentalism. Determinism: This concept was developed by German Geographer Friedrich Ratzel, which was further expanded by Ellsworth Huntington. This approach is based on the concept of ‘nature controls human’ or ‘earth made human’. This is also known as environmental determinism. According to this approach, human being is largely influenced by nature. In fact, the determinism states that human being is subordinate to natural environment because all aspects of human life such as physical (health and well-being), social, economic, political, ethical and aesthetic not only depend on but are dominantly controlled by the physical environment. Possibilism: This term was coined by the French historian, Lucien Febvre. Possibilism approach in the study of human-environment relationship is an offshoot of the criticism of environmental determinism. The evolution of such human-environment relationship was influenced by the advancement of science and technology. Possibilism indicates that the physical environment is passive and human being is the active agent at liberty to choose between wide ranges of environmental possibilities. According to this apporach, the pattern of human activity is the result of the initiative and mobility of human being operating within the natural framework. However, it was agreed upon by the possibilists that humans lack the abilities to fully tame the nature and is not always victorious over it. As a result of the above, some scientists and academics vouched for ‘cooperation with nature’ or ‘mutual interaction’ between human being and environment. Environmentalism or Ecological Approach: This approach is based upon the basic principle of ecology, which is the study of mutual interaction between organisms and physical environment on the one hand, and the interaction among the organisms on the other in a given ecosystem. This approach describes human being as an integral part of nature or environment. Human being as the most skilled and intelligent has a unique role to play in maintaining a natural environment as healthy and productive as it should be. This approach emphasizes on wise and restrained use of natural resources and application of appropriate environmental management programmes, policies and strategies keeping in view certain basic principles of ecology so that already depleted natural resources are replenished, and health and productivity of the nature is restored. The ecological approach is best reflected in the concept of sustainable development which we will discuss in the following section. SAQ 2 Fill in the blanks with suitable words: i) The approach of determinism is based on the concept of..................... 12............... or............................. Unit 1 Our Environment.......................................................................................................................................................................... ii) Possibilism indicates that the physical environment is............................... and human being is the.................................. agent at liberty to choose between wide ranges of environmental possibilities. iii) Environmentalism emphasizes on........................................ and........................................... use of natural resources. 1.5 CONCEPT OF SUSTAINABILITY AND SUSTAINABLE DEVELOPMENT The concept of Sustainable Development was formally defined in the report titled “Our Common Future”. This report was an outcome of deliberation of a group constituted by World Commission on Environment and Development (WCED) and chaired by the then Norwegian Prime Minister Gro Harlem Brundtlandt. Brundtlandt Commission defined sustainable development as the development that involves “…meeting the need of present generation without compromising the ability of future generations to meet their own needs.” This definition of sustainable development initiated a lot of debate. The scientists were of the opinion that the term ‘need’ and ‘development’ has not been defined properly in the report. Need can not be generalized universally. It varies from place to place and person to person. Similarly, development was also not properly defined. The report explains development as something people do to improve their lives. Therefore, it becomes amenable to varied interpretations. A more precise definition with clearly spelt-out goals remains elusive. Herman Daly, an ecological economist, referred to sustainable development as an “oxymoron”. Do you know what an Oxymoron is? Oxymoron is a figure of speech that combines two usually contradictory terms into a compressed paradox (e.g. bitter sweet, pretty ugly). The definition of ‘development’ is not precise enough to make it more in favour of nature conservation than on building roads, factories, infrastructure etc. The Oxford dictionary meaning of development is “a stage or advancement”. On the other hand, “sustainability” is the capacity to endure. The word “sustainability” is derived from the latin “sustinere” (tenere = to hold; sus= up). Dictionaries provide more than ten meanings for sustain, the main ones being to “maintain”, “support”, or “endure”. Further more, as has been pointed out by Michael Redclift the sustainability discussion has gradually, over the years, moved almost imperceptibly away from “human needs” to “human rights”. Therefore, Sustainability refers to a process which can be continued indefinitely without depleting the resource base on which it depends. Therefore, it is the practical goal towards which our interaction with the natural world should be directed. The guiding principles of sustainability cut across ecological, economic, social and cultural dimensions. The concept of sustainable development is now well accepted at international, national and local levels. This has been emerging as a strong alternative model of development after a long debate and discussion since Rio Summit in 13 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... 1992. Sustainable development means different things to different people. There are three important disciplines traditionally concerned with the processes involved in conceptualizing sustainable development. The discipline of economics is mainly concerned with growth, efficiency and the optimum use of resources. On the other hand, sociologists mainly focus on human needs and on concepts like equity, empowerment and social cohesion. Ecologists show their greatest concern for preserving natural systems, for living within the carrying capacity of the environment, and for dealing efficiently with pollution. Today this sectarian approach to development adopted by the above mentioned disciplines have been rejected. Now, it has been argued that sustainable development will be achieved where the concerns of these three groups are addressed in a holistic manner, as shown in Fig. 1.3. Fig. 1.3: Three Pillars of Sustainable Development. It has been said that sustainable development is an ideal which no societies today have achieved anything resembling it. Nevertheless, as with justice, equality, and freedom, it is important to uphold sustainable development as an ideal - a goal toward which all human societies need to be moving. For example, policies and actions that reduce infant mortality, increase the availability of family planning, improve the air quality, provide more abundant and pure water, preserve and protect natural ecosystems, reduce soil erosion and reduce the release of toxic chemicals to the environment, all movea society in the right direction – toward a sustainable future. To achieve this desired goal, societies have to make certain transitions which are very much essential. There is a broad consensus on the following transition to make future societies:  A demographic transition: from a continually growing population to one that is stable.  A resource transition to an economy that is not solely obsessed with growth, rather relies more on nature’s income and protects ecosystem 14 capital from depletion. Unit 1 Our Environment..........................................................................................................................................................................  A technological transition from pollution-intensive economic production to environment friendly processes.  A political/sociological transition  A community transition Priority Areas for Achieving Sustainable Development 1. Slow Down Population Growth: This is essential for addressing all the other priority areas. 2. Reduce Poverty, Inequality and Third World Debt: Improving health, longevity and literacy, increasing employment etc. This is important for curbing the loss of species, the extent of land degradation and water pollution. 3. Make Agriculture Sustainable: This includes reducing soil erosion and decreasing the use of harmful agricultural practices. This is important for curbing the loss of biodiversity, land degradation and pollution. 4. Protect Forests and other Habitats: This includes reforestation and afforestation of wastelands, protection of other living resources, control greenhouse gases and ozone layer depletion. This is important for reducing air pollution, land degradation, depletion of energy and minerals 5. Make Water and Energy Use Sustainable: This includes improved energy efficiency, conserving energy and developing renewable energy resources. This is important for reducing air pollution, land degradation, depletion of energy and minerals. 6. Make Water Use Sustainable: This includes improving the efficiency of water use and protecting water quality. This is important for curbing water pollution and depletion and land degradation. 7. Reduce Waste Generation: This includes improving production processes, waste treatment and recycling processes. This is important for reducing air and water pollution and energy, mineral and water depletion. SAQ 3 i) Define the term ‘‘Sustainability’’. ii) Why is it important to uphold sustainable development as an ideal? 1.6 MULTIDISCIPLINARY NATURE OF THE ENVIRONMENTAL STUDIES Till now, you must have realised that the environment affects us in several ways, for example, the water we consume, the air we breathe, the climatic conditions in which we live, and surrounding where we live all have effects on us. In natural conditions usually living organisms keep a balance with their environment. Humans in many ways have personalized the environment 15 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... according to their need with the help of skill and science, but in doing so we have disrupted the fragile intricately woven web of life and life supporting systems. All these interactions with environment as a whole are subjects of environmental studies.Therefore,environmental studies contribute a branch of study of inherent or induced changes in the environment, and their effect on living beings. Environmental studies cover a large domain of knowledge which deals with every concern that affects an organism. From human angle, this means it is an applied science which seeks all possible answers to make human civilization sustainable on the earth with all its limited resources. It includes not only the study of physical and biological characters of the environment but also economic, social, cultural and even political and legal aspects of the environment. Various issues such as clean and safe drinking water, clean and fresh air, clean living conditions, productive land, good quality foodstuff and sustainable development are dealt with in environmental studies. The importance of environmental studies cannot be disputed. The need for sustainable development is a key to the future of humankind. Continuing problems of pollution, loss of forest and bio-diversity, solid waste disposal, degradation of environment, issues like global warming and climate change, the depletion of ozone layer and loss of biodiversity have made everyone aware of environmental issues. The United Nations Conference on Environment and Development held in Rio de Janerio in 1992 and World Summit on Sustainable Development at Johannesburg in 2002 have drawn the attention of people around the globe to the deteriorating condition of our environment. This has been again reaffirmed by United Nations by adopting seventeen Sustainable Development Goals in the year 2015. It has been decided that these seventeen goals would be achieved in the next fifteen years i.e. 2016-2030. Box 1.1: Sustainable Development Goals 1. No Poverty 2. Zero Hunger 3. Good Health and Wellbeing 4. Quality Education 5. Gender Equality 6. Clean Water and Sanitation 7. Affordable and Clean Energy 8. Decent Work and Economic Growth 9. Industry, Innovation and Infrastructure 10. Reduced Inequalities 11. Sustainable Cities and Communities 12. Responsible Consumption and Production 13 Climate Action 14. Life Below Water 15. Life on Land 16. Peace, Justice and Strong Institution 17. Partnership for the Goals. 16 Unit 1 Our Environment.......................................................................................................................................................................... India is rich in biodiversity which provides various resources for people. Only about 1.7 million living organisms have been described and named globally. Still many more remain to be identified and described. Attempts are made to conserve them in ex-situ(outside their natural habitat) and in-situ(in their natural habitat situations). You will learn about in-situand ex-situ conservation in Unit 8.Destruction of habitats, over-use of energy resources and environmental pollution has been found to be responsible for the loss of a large number of life-forms. It is feared that a large proportion of life on earth may get wiped out in the near future. These issues are extensively addressed in the next thirteen units of this course both at global as well as national level. 1.7 IMPORTANCE OF ENVIRONMENTAL STUDIES The environment studies enlighten us, about the importance of protection and conservation of environment. At present, due to our aggressive consumerist lifestyle and carbon intensive industrial development we have created a large number of environment issues both in terms of magnitude, intensity and complexity at local, regional and global level. We shall study about these issues and suggestive measures for mitigation in the Environment Studies. Let us discuss major environmental as issues in the following paragraphs: 1. Environmental issues are of international importance: It has now been well recognised that environment issues like global warming, climate change, ozone layer depletion, acid rain, marine pollution and loss of biodiversity are not merely national issues but are global issues and hence must be tackled with international efforts and cooperation. 2. Emergence of problems in the wake of modernisation and development: Development in the modern period has given birth to industrialisation, urbanization, modern transportationsystems, Agriculture, Housing etc. When the West developed, it did so perhaps in ignorance of the environmental impact of its activities. Evidently such a path is neither practicable nor desirable. The developing world now faces the challenge of developing without environmental degradation. 3. Explosive increase in population: World census reflects that one in every seven persons in this planet lives in India.Evidently with 16 per cent of the world’s population and only 2.4 per cent of its land area,there is a heavy pressure on the natural resources including land. This emphasizes on the need for efficient management of natural resources for the benefits of all. 4. Need for an alternative solution: It is essential, especially for developing countries to find alternative paths to developmental goal. Such a goal would need to be distinct from the developed world in the manner that would conserve natural resources and avoid wasteful consumption. 5. Need for wise planning of development: Resources withdrawal, processing and use of theproducts have all to be synchronised with the 17 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... ecological cycles in any plan of development. Our actions should be planned for the sustenance of the environment and development. SAQ 4 i) Differentiate between in-situ and ex-situ conservation. ii) What should be kept in mind while planning for alternative solution in developing countries for the sustenance of environment and development? 1.8 SUMMARY  Environment is defined as”the sum total of living and non-living components; influences and events surrounding an organism”. Broadly the environment comprises of abiotic (non-living) and biotic (living) components.  Brundtlandt Commission define sustainable development as the development that provides for “…meeting the need of present generation without compromising the ability of future generation to meet their own needs.”  It has been said that sustainable development is an ideal which no societies have been able to achieve. Nevertheless, as with justice, equality, and freedom, it is important to uphold sustainable development as an ideal- a goal toward which all human societies need to be moving.  Sustainability refers to a process which can be continued indefinitely without depleting the resource base on which it depends. Therefore, it is the practical goal towards which our interaction with the natural world should be working. The guiding principles of sustainability cut across ecological, economic, social and cultural dimensions and there are obvious trade-offs.  The environment studies enlighten us about the importance of protection and conservation of environment. At present, due to our aggressive consumerist lifestyle and carbon intensive industrial development, we have created a large number of environment issues both in terms of magnitude, intensity and complexity at local, regional and global level. As a result, the quality of life and even survival of humankind on earth are threatened. We study about these issues and suggestive measures for mitigation in the Environment Studies. 1.9 TERMINAL QUESTIONS 1. What is environment? Explain various components of environment with 18 suitable examples. Unit 1 Our Environment.......................................................................................................................................................................... 2. Analyse human-environment relationship over time and space. 3. Describe in detail priority areas required for achieving sustainable development. 4. Explain in detail the importance of environmental studies. 1.10 ANSWERS Self-Assessment Questions 1. i) The physical components set the condition for the survival of the biotic components. ii) Environment provides all life supporting elements which include air to breathe, food we eat and water we drink, and shelter either as natural like caves and tree holes or material for the construction of as artificial dwellings. 2 i) nature controls human, earth made human ii) Passive, active iii) wise, restrained 3. i) Sustainability refers to a process which can be continued indefinitely without depleting the resource base on which it depends. ii) A goal toward which all human societies need to be moving. 4. i) In-situ refers to conservation in their natural habitat situations. whereas ex-situ refers to conservation outside their natural habitat. ii) While planning for alternative solution in developing countries for the sustenance of environment and development need to be distinct from the developed world in the manner that would conserve natural resources and avoid wasteful consumption. Terminal Questions 1. Environment is defined as the sum total of living and non-living components; influences and events surrounding an organism. It has two components i.e. biotic and abiotic. Biotic components include all living organisms whereas abiotic component includes non-living things. Examples of abiotic components are topography, light, precipitation, humidity & water, temperature, atmospheric gases, seasonal changes whereas biotic components include plant, animals including humans, parasites and micro-organisms and decomposers. 2. Human-environment relationship can be grouped under three categories i.e. determinism, possibilism and environmentalism. Determinism states that human being is subordinate to natural environment because all aspects of human life are dominantly controlled by the physical 19 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... environment. Possibilism indicates that the physical environment is passive and human being is the active agent at liberty to choose between wide ranges of environmental possibilities.Ecological his approach emphasizes on wise and restrained use of natural resources and application of appropriate environmental management programmes, policies and strategies keeping in view certain basic principles of ecology so that already depleted natural resources are replenished, and health and productivity of the nature is restored. 3. Priority areas required for achieving sustainable development are slow down population growth;reduce poverty, inequalityand Third World debt;make agriculture sustainable;protect forest and other habitats;make water and energy use sustainable;reduce waste generation. 4. Importance of environmental studies are as follows: (i) Environment issues are of international importance; (ii) Emergence of problems in the wake of modernisation and development; (iii) explosive increase in population; (iv) need for an alternative solution; and (v) need for wise planning of development Any four) 1.11 FURTHER READING 1. Bharucha, E. (2005) Textbook of Environmental Studies for Undergraduate Courses, Hyderabad: Universities Press (India) Private Limited. 2. Botkin, D. B. & Keler, E. A. 8th Ed. (2011) Environmental Science: Earth as a Living Planet, New Delhi: Wiley India Pvt. Ltd. 3. Kaushik, A. 2nd Ed. (2004) Environmental Studies, New Delhi: New Age International (P) Limited. 4. Rajagopalan, R. 3rd Ed. (2015) Environmental Studies, New Delhi: Oxford University Press. 5. Redy, M. A. (2007) Text Book of Environmental Science and Technology, Hyderabad: BS Publications. 6. Wright, R. T. (2008) Environmental Science: Towards a Sustainable Future, New Delhi: PHL Learning Private Ltd. 20 Unit 2 Ecosystems 2.......................................................................................................................................................................... UNIT ECOSYSTEMS Structure 2.1 Introduction 2.6 Nutrient Cycles Expected Learning Outcomes Gaseous Cycles 2.2 What is an Ecosystem? Sedimentary Cycles Definition of Ecosystem 2.7 Ecological Succession Ecosystem Features Types of Ecological Succession Size of an Ecosystem Primary Succession Largest Ecosystem: Biosphere Secondary Succession 2.3 Components of the Ecosystem 2.8 Ecosystem and Human Intervention Abiotic Components 2.9 Summary Biotic Components 2.10 Terminal Questions 2.4 Trophic Levels 2.11 Answers Food Chain 2.12 Further Reading Types of Food Chain 2.5 Ecosystem Functioning 2.1 INTRODUCTION Earth is the only planet, revolving around the sun, which is known to support life. Despite the vastness of earth, life exists only in a very thin layer enveloping the earth called biosphere. Sun is the only source of energy which enables continuous interaction among various life forms. In the previous unit you have already learnt about the word ‘environment’ and its definition. You have also been familiarised with the external and internal environment of organisms that also include us. Both the external and the internal environment of an organism have an impact on its existence and survival. The components of the external environment of an organism include physical as well as living components. The action and interaction of the physical and living components of an organism make a system of relationship called ecosystem. This unit deals with the structure and properties of ecosystem, basic concepts of ecosystem functioning, and the factors controlling it. It also deals with the development of ecosystem. The unit will familiarise you with interactions like competition, parasitism and mutualism that exist between living beings. This unit will also focus on how we as living beings interact with other living and nonliving components of the ecosystem. You will also 21 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... become aware that ecosystems are able to maintain homeostasis by active effort, resisting the tendencies toward disorder. For centuries humans have considered the earth and the environment as a virtually unlimited resource but subtle and gradual changes have altered our environment in many different ways. We wish that this unit enables you to use your intelligence and skills to the best of your advantage for managing our environment and keeping it healthy for future generations. Expected Learning Outcomes After completing the study of this unit you should be able to:  define and explain the basic concept of ecosystem, its structure, function, and properties;  explain the terms biosphere, biome, aquatic zone, landscape and population;  describe the development, control and stability of the ecosystem in order to act positively towards the environment;  discuss that the flow of energy and cycling of material are central to ecosystem functioning and indiscriminate intervention would lead to damage and disruption of the environment; and  explain your duties and obligations towards the environment. 2.2 WHAT IS AN ECOSYSTEM? You and I, as you know, live in a defined area of the earth where plants and animals, including ourselves, develop relationships with each other for life, food, water, shelter and mates. This discrete unit has both living and non-living environmental components, which are interdependent and interrelated in terms of their structure, components and functioning. Such a discrete unit is called an ecosystem. 2.2.1 Definition of Ecosystem The word ecosystem, An ecosystem is defined as, “any unit (a biosystem) that includes all the was coined by Prof. organisms that function together (the biotic community) in a given area, Arthur Tamsley in interacting with the physical environment (abiotic component) so that the flow 1935. The prefix ‘eco’ of energy clearly leads to defined biotic structures and cycling of materials means environment. between living and nonliving parts”. The ecosystem is thus, a dynamic system which involves the interactions between living and non-living components of an ecosystem and includes the input, transfer, storage and output of energy as well as cycling of essential materials through the ecosystem. All the processes that occur in the ecosystem are energy dependent. Fig. 2.1 illustrates this beautifully. Ecosystems differ greatly in composition, in the number and kinds of species, in the kinds and relative proportions of non-biological constituents and in the degree of variation in time and space.The study of an ecosystem is based on 22 its structure and function. Unit 2 Ecosystems.......................................................................................................................................................................... Fig. 2.1: Schematic representation of an ecosystem. The dotted lines represent the boundary of the system. The three major components are the producers, the consumers, and the abiotic elements. The arrows indicate interactions within the system and with the enviroment. Energy does not cycle because all the energy of the ecosystem is derived from the sun and it dissipates as heat. 2.2.2 Ecosystem Features Ecosystems have both structural and functional features some of which you have studied in Unit 1, and others which you will study in this unit. You will learn about some other aspects in the forthcoming units. The ecosystem features are as follows: I. Structural Features The Structural aspect of the ecosystem refers to all the elements that make up an ecosystem – the individuals and communities of plants and animals and the non-living factors present in the ecosystem. The structural components include: A. Abiotic components (Non-living Components): i) Inorganic compounds – carbon, nitrogen, carbon dioxide, water. ii) Organic compounds – proteins, carbohydrates, lipids, which link the abiotic to biotic components. iii) Climatic regimes – temperature, moisture, light and topography B. Biotic Components (Living Components): i) Producers – plants ii) Consumers – primary, secondary, tertiary. iii) Decomposers – saprotrophs II. Functional Features Functional aspects refer to all the processes and interactions performed by the organisms in an ecosystem and include: i) Energy cycles ii) Food chains iii) Diversity – interlinks between organisms iv) Nutrient cycles – biogeochemical cycles v) Succession 23 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... 2.2.3 Size of an Ecosystem Ecosystems may vary in size from the smallest puddle of water or a terrestrial habitat, to a landscape or large forest, a biome, or even the entire global biosphere or ecosphere (Fig 2.2). Fig. 2.2 : Size of ecosystem in decreasing order: Biosphere, biome, landscape, ecosystem, community, population, individual. 2.2.4 Largest Ecosystem: Biosphere Before we explain the functioning of the components of the ecosystem, let us first discuss the largest ecosystem, namely, “the biosphere”. Biosphere is that part Biosphere, also called ecosphere, is that part, of the earth, water and of the earth where life atmosphere in which many smaller ecosystems exist and operate. The three can exist. It is a main subdivisions of the biosphere are: (1) lithosphere (land); narrow layer around the surface of the earth. If (2) hydrosphere (water); (3) atmosphere (air) or the gaseous envelope of you visualise the earth the earth which extends up to a height of 22.5 km. Fig. 2.3 shows the idealised to be the size of an apple the biosphere scheme of biosphere in relation to hydrosphere, atmosphere and lithosphere. would be as thick as The area of contact and interaction between these three components is really its skin. important for life, as it is here that the entire life is confined and the basic processes of life, like photosynthesis and respiration occur. Fig 2.3: Idealised scheme of a biosphere in relation to hydrosphere, 24 atmosphere and lithosphere. Unit 2 Ecosystems.......................................................................................................................................................................... The biosphere extends from the floor of the ocean some 11,000 metres below the surface of the earth to the top of the highest mountains, or about 9,000 metres above the mean sea level. Its most densely populated region is just above and below the sea level. Life in the biosphere is abundant between 200 Biosphere is absent at extremes of the North metres (660 feet) below the surface of the ocean and about 6,000 metres and South poles, the (20,000 feet) above sea level. highest mountains and the deepest oceans, Living organisms are not uniformly distributed throughout the biosphere. Only since existing conditions there do not a few organisms live in the polar regions, while the tropical rain forests support life. possess an exceedingly rich diversity of plants and animals. The nutrients Occasionally spores of necessary for living organisms come from air, water and soil and not from fungi and bacteria do occur at great height outside. The same nutrients that are present in the biosphere are recycled beyond 9,000 metres, over and over again for life to continue. The energy required for the life within but they are not the biosphere comes from the sun without which the biosphere will collapse. metabolically active, and hence represent The terrestrial part of the biosphere is divisible into enormous regions called only dormant life. biomes, which form vast ecosystems and are characterized, by climate, vegetation, animal life and general soil type. The dozen or more biomes of the earth are spread over millions of square kilometres and span entire continents. 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 that determine the boundaries of the biomes are temperature and precipitation (rain or snow). Aquatic systems are also divided into distinct aquatic life zones, which however are not called biomes but are very similar. The aquatic life zone are regions of relatively distinct plant and animal life. The major difference between the various aquatic zones is due to salinity, levels of dissolved nutrients, water temperature and depth of sunlight penetration. You will learn about the different types of terrestrial ecosystems namely biomes and aquatic life zones on our earth in Unit 3. SAQ 1 1. a) In the following statements, put a tick ( ) mark on the correct ones and a cross ( x ) on the wrong ones in the given boxes. i) An ecosystem is a natural unit of study, consisting of a community of organisms (biotic components) and the non-living environmental factors (abiotic components). ( ) ii) All ecosystem have well-defined boundaries. ( ) iii) Ecosystems represent enormous contrast in size and complexity. ( ) iv) An ecosystem having autotrophs and heterotrophs but no decomposers could be self-contained. ( ) v) Ecosystems are self-sustaining because they are well insulated from outside influences. ( ) 25 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... b) Arrange the following sub-components of an ecosystem: energy, consumers, environment, inorganic elements, decomposers, primary producers and soil.................................. Biotic components ?................................. ?................................. Ecosystem................................. ?................................. Abiotic components ?................................. 2.3 COMPONENTS OF THE ECOSYSTEM Each biome or aquatic zone can be subdivided into smaller units called “ecosystem”. An ecosystem is thus, a subdivision of biome and can also be called an ecological system. Recall the definition of an ecosystem from subsection 2.2.1. Any complete definition of an ecosystem includes the biotic as well as the abiotic components and the interaction between the two. For example the desert biome of Rajasthan contains the Thar Desert ecosystem which is characterised by arid conditions, sandy terrain, and succulent plants. Animals found there are lizards and snakes. Similarly, a pond is also an ecosystem of the freshwater aquatic zone and would be characterized by a lentic (standing) fresh water body containing aquatic organisms and plants. The various kinds of organisms that inhabit an ecosystem form its populations. In ecology, ‘a population is a group of potentially interbreeding individuals that occur together in space and time’. The individual comprising a population are members of the same species. If you look around yourself, you will notice that populations 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. A population of squirrels would require fruits and nuts for food and trees for shelter. Even plants cannot exist by themselves; for example, they require animals for seed dispersal and pollination, and soil microorganism to facilitate nutrient supply to them through decomposition. In nature ‘an aggregation of populations of different species (plant and/or animals) in an area, living together with mutual tolerance and beneficial interactions amongst themselves and with their environment, form a biotic community. Communities in most instances are named after the dominant plant form species. A grassland, for example, is dominated by grasses, though it may contain herbs, shrubs, and trees, along with associated animals of different species. Communities may be large or small. 26 Unit 2 Ecosystems.......................................................................................................................................................................... 2.3.1 Abiotic Components You will recall, having read earlier that the physical or abiotic components are the inorganic and non-living parts of the ecosystem. Each of these abiotic factors may be studied individually, however, each of these factor is influenced by and in turn influences all the other factors. 2.3.2 Biotic Components The biological or biotic components of an ecosystem interact in an abiotic background (Fig. 2.4) and include: Food refers to complex organic compounds 1. Producers/Autotrophs such as carbohydrates, Chlorophyll bearing green plants, green and purple bacteria and blue proteins and fats. Green plants first green algae are the main biological or biotic members in nature which produce simple manufacture their own food from simple inorganic substances by the carbohydrates like process of photosynthesis. In this process the chlorophyll bearing glucose and later various complex organisms in the presence of sunlight take up atmospheric carbon carbohydrates. dioxide through their leaves and combine with water to produce organic substances or food. Chemosynthetic bacteria also synthesise their own food but instead of the sun energy they use simple chemicals released from the interior of the earth to prepare food by the process of chemosynthesis. Organisms that are able to manufacture their own food are called autotrophs or producers. 2. Consumers/ Heterotrophs All other organisms that are unable to make their own food but depend on other organisms for food to meet their energy needs for survival are called heterotrophs or phagotrophs or consumers. Among consumers, animals such as goat, cow, deer, rabbit and insects like grasshoppers which eat green plants are called primary consumers or herbivores. Organisms which eat a herbivore, like a bird that eats grasshoppers are carnivores as they eat other animals. These carnivores are also called secondary consumers. Carnivorous organisms like cats which eat secondary consumers like birds are called tertiary consumers. Thus, while the primary consumers are herbivores, the secondary and tertiary consumers are carnivores. Animals like tigers, lions, and vultures which are not killed or eaten by other animals are top carnivores. 3. Decomposers or Saprotrophs or Reducers Both the consumers and producers complete their life cycles and die and new generation of their population develop. You must be wondering what happens to the dead organisms. In the ecosystem there is a continuous breaking up or decomposition of the organic matter of the dead organisms and there is a continuous cycling of materials. Certain Fragments of bacteria which are micro organisms and some fungi are responsible for decomposing organic matter are called the decomposition and recycling of material. The organisms are called detritus decomposers or saprotrophs or reducers. Most of the saprotrophs are microscopic and all are heterotrophic in nature. The role of decomposers is very essential and important. 27 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... Fig. 2.4: Biotic factors are dependent on abiotic factors. Light and heat energy from the sun are the main key components that biota depend on. Biomass of producers is used by consumers who obtain energy by ingesting food. The assimilated energy is used for various functions of the body like respiration and movements. When the organism dies the energy stored in tissues is used by the decomposers. 2.4 TROPHIC LEVELS You are now aware that an ecosystem is considered as a discrete unit, where complex natural community obtains food directly or indirectly from plants through one, two, three or four steps and accordingly these steps are known as the first, second, third and fourth trophic (trophe = nourishment) levels or food levels (Fig. 2.5). A trophic level refers to a position or a level in a food chain or ecological pyramid. It is occupied by a group of organisms that have a similar feeding mode. Trophic levels are numbered according to the number of steps or levels an organism is away from the source of food or energy that is the producer. A food chain would start at trophic level 1. Similarly the base of an ecological pyramid is also at trophic level I. The trophic level 1 is occupied by the primary producers that are referred to as autotrophs. The next trophic level in Humans, being omnivores, may a food chain or ecological pyramid is trophic level II which consists of belong to more than organisms that feed on the primary producers and are referred to as primary one trophic level. consumers, or heterotrophs or herbivores.Trophic levels III,IV and V would be occupied be occupied by carnivores. Given below are the probable numbers of trophic levels that can exist in an ecosystem and the types of organism groups that occupy the various trophic levels: Green plants (producers); trophic level I – Autotrophs  Herbivores (primary consumers); trophic level II – Heterotrophs  Carnivores (secondary consumers); trophic level III – Heterotrophs  Carnivores (tertiary consumers); trophic level IV – Heterotrophs 28  Top carnivores (quarternary consumers); trophic level V – Heterotrophs Unit 2 Ecosystems.......................................................................................................................................................................... Energy derived from food thus, also flows through the trophic levels: from producers to subsequent trophic levels (Fig. 2.5). This energy always flows from lower (producer) to higher (herbivore, carnivore etc.) trophic levels. It never flows in the reverse direction. Furthermore there is a loss of some energy in the form of unusable heat at each trophic level so that the energy level decreases from the first trophic level upwards. As a result there are usually four or five trophic levels and seldom more than six as beyond that very little energy is left to support any organism. Fig. 2.5: Trophic levels in a food chain in: i) a terrestrial and an ii) aquatic environment. SAQ 2 a) Give two examples each of organisms that occupy the first, second and third trophic levels. b) Pick an animal of your choice and show how it can occupy several different trophic levels? 2.4.1 Food Chain You now know from the previous section that organisms in the ecosystem are Each link in the food related through feeding or trophic levels, that is one organism becomes food chain can also be called a trophic level. for the other. The transfer of food energy from one trophic level to another trophic level in an ecosystem by the repeated process of eating and being eaten is known as food chain. The food chain can thus be defined as a linear sequence of links of organisms in which an organism becomes food for the next organism (Fig. 2.6, 2.7and 2.8). The arrows in these three figures denote the direction and movement of nutrients and energy from producer to consumer. Similar to the trophic levels and for the same reasons the links or steps in a food chain are usually upto four or five. 2.4.2 Types of Food Chains In nature, three main types of food chains have been distinguished: 29 Block 1 An Introduction to Environment and Environmental Studies.......................................................................................................................................................................... i) Grazing Food Chain: In this type of food chain the primary consumers, are herbivores and use the plant or plant part as their food. This food chain begins from green plants. An example of such a food chain is given below (Fig. 2.6): Fig. 2.6: A grazing food chain designated as follows: Grass grasshopper frog snake eagle. In a community of ii) Detritus Food Chain: This type of food chain starts from dead organic organisms in a shallow matter of decaying and metabolic wastes of animals and plant bodies area of the sea, about called detritus to the micro-organisms which are primary detritus feeding 30% of the total energy flows via detritus organism called detrivores or decomposer then to secondary detritus chains. In a forest with