UNIT 3: Ecosystems 3.1 CONCEPT OF AN ECOSYSTEM 54 3.1.1 Understanding ecosystems 55 3.1.2 Ecosystem degradation 55 3.1.3 Resource utilisation 56 3.2 STRUCTURE AND FUNCTIONS OF AN ECOSYSTEM 56 3.3 PRODUCERS, CONSUMERS AND DECOMPOSERS 57 3.4 ENERGY FLOW IN THE ECOSYSTEM 58 3.4.1 The water cycle 58 3.4.2 The Carbon cycle 59 3.4.3 The Oxygen cycle 60 3.4.4 The Nitrogen cycle 60 3.4.5 The energy cycle 61 3.4.6 Integration of cycles in nature 62 3.5 ECOLOGICAL SUCCESSION 62 3.6 FOOD CHAINS, FOOD WEBS AND ECOLOGICAL PYRAMIDS 62 3.6.1 The food chains 62 3.6.2 The food webs 63 3.6.3 The ecological pyramids 63 3.7 INTRODUCTION, TYPES, CHARACTERISTIC FEATURES, STRUCTURE AND FUNCTIONS 63 3.7.1 Forest ecosystem 65 3.7.2 Grassland ecosystem 70 3.7.3 Desert ecosystem 74 3.7.4 Aquatic ecosystems (ponds, lakes, streams, rivers, estuaries, oceans) 75 Ecosystems 53 Chapter3.p65 53 4/9/2004, 5:08 PM 3.1 CONCEPT OF AN ECOSYSTEM the Western and Eastern Ghats, the semi-arid desert in the West, the Deccan Plateau, the An ‘Ecosystem’ is a region with a specific and Coastal Belts, and the Andaman and Nicobar recognizable landscape form such as forest, Islands. These geographically distinctive areas grassland, desert, wetland or coastal area. The have plants and animals that have been adapted nature of the ecosystem is based on its geo- to live in each of these regions. graphical features such as hills, mountains, plains, rivers, lakes, coastal areas or islands. It is At an even more local level, each area has sev- also controlled by climatic conditions such as the eral structurally and functionally identifiable eco- amount of sunlight, the temperature and the systems such as different types of forests, grass- rainfall in the region. The geographical, climatic lands, river catchments, mangrove swamps in and soil characteristics form its non-living (abi- deltas, seashores, islands, etc. to give only a few otic) component. These features create condi- examples. Here too each of these forms a habi- tions that support a community of plants and tat for specific plants and animals. animals that evolution has produced to live in these specific conditions. The living part of the Ecosystems have been formed on land and in ecosystem is referred to as its biotic component. the sea by evolution that has created species to live together in a specific region. Thus ecosys- Ecosystems are divided into terrestrial or land- tems have both non-living and living compo- based ecosystems, and aquatic ecosystems in nents that are typical to an area giving it its own water. These form the two major habitat condi- special characteristics that are easily observed. tions for the Earth’s living organisms. Definition: The living community of plants and All the living organisms in an area live in com- animals in any area together with the non-liv- munities of plants and animals. They interact ing components of the environment such as soil, with their non-living environment, and with each air and water, constitute the ecosystem. other at different points in time for a large num- ber of reasons. Life can exist only in a small pro- Some ecosystems are fairly robust and are less portion of the earth’s land, water and its atmo- affected by a certain level of human disturbance. sphere. At a global level the thin skin of the earth Others are highly fragile and are quickly de- on the land, the sea and the air, forms the bio- stroyed by human activities. Mountain ecosys- sphere. tems are extremely fragile as degradation of forest cover leads to severe erosion of soil and At a sub-global level, this is divided into bio- changes in river courses. Island ecosystems are geographical realms, eg. Eurasia called the easily affected by any form of human activity palaeartic realm; South and South-East Asia (of which can lead to the rapid extinction of sev- which India forms a major part) is the Oriental eral of their unique species of plants and ani- realm; North America is the Nearctic realm; mals. Evergreen forests and coral reefs are also South America forms the Neotropical realm; examples of species rich fragile ecosystems Africa the Ethiopian realm; and Australia the which must be protected against a variety of Australian realm. human activities that lead to their degradation. River and wetland ecosystems can be seriously At a national or state level, this forms biogeo- affected by pollution and changes in surround- graphic regions. There are several distinctive ing landuse. geographical regions in India- the Himalayas, the Gangetic Plains, the Highlands of Central India, 54 Environmental Studies for Undergraduate Courses Chapter3.p65 54 4/9/2004, 5:08 PM 3.1.1 Understanding ecosystems • ‘How does the ecosystem work’? The ecosystem functions through several Natural ecosystems include the forests, grass- biogeochemical cycles and energy transfer lands, deserts, and aquatic ecosystems such as mechanisms. Observe and document the ponds, rivers, lakes, and the sea. Man modified components of the ecosystem which con- ecosystems include agricultural land and urban sists of its non-living or abiotic features such or industrial land use patterns. as air, water, climate and soil. Its biotic com- ponents, the various plants and animals. Each ecosystem has a set of common features Both these aspects of the ecosystem inter- that can be observed in the field: act with each other through several func- tional aspects to form Nature’s ecosystems. • ‘What does the ecosystem look like?’ Plants, herbivores and carnivores can be One should be able to describe specific fea- seen to form food chains. All these chains tures of the different ecosystems in ones are joined together to form a ‘web of life’ own surroundings. Field observations must on which man depends. Each of these use be made in both urban and natural sur- energy that comes from the sun and pow- roundings. ers the ecosystem. • What is its structure? Is it a forest, a grassland, a water body, an 3.1.2 Ecosystem degradation agricultural area, a grazing area, an urban area, an industrial area, etc.? Ecosystems are the basis of life itself! The natu- ral ecosystems in the wilderness provide a vari- What you should see are its different char- ety of products and are regions in which a num- acteristics. A forest has layers from the ber of vital ecological processes are present, ground to the canopy. A pond has differ- without which human civilization would not be ent types of vegetation from the periphery able to exist. to its center. The vegetation on a mountain changes from its base to its summit. Ecosystems are however frequently disrupted by human actions which lead to the extinction of • What is the composition of its plant and species of plants and animals that can live only animal species? in the different natural ecosystems. Some spe- List the well-known plants and animals you cies if eliminated seriously affect the ecosystem. can see. Document their abundance and These are called ‘keystone’ species. Extinction numbers in nature: very common, common, occurs due to changes in land use. Forests are uncommon, rare. Wild mammals will not deforested for timber, wetlands are drained to be seen in large numbers, cattle would be create more agricultural land and semi arid common. Some birds are common – which grasslands that are used as pastures are changed are the most common species? Insect spe- into irrigated fields. Pollution from industry and cies are very common and most abundant. waste from urban settings can also lead to ex- In fact there are so many that they cannot tinction of several species. be easily counted. The reason for the depletion of natural resources is twofold – our rapidly exploding population that needs to sustain itself on resources, and the growth of affluent societies, which consume Ecosystems 55 Chapter3.p65 55 4/9/2004, 5:08 PM and waste a very large proportion of resources The key to this issue is the need for an ‘equi- and energy. Increasing extraction of resources table’ distribution of all types of natural re- is at the cost of natural ecosystems, leading to a sources. A more even sharing of resources within derangement of their important functions. Each the community can reduce these pressures on of us in our daily lives use a variety of resources. the natural ecosystems. If tracked back to their source, one finds that the resources were originally obtained from nature and natural ecosystems. Our insensitiv- 3.2 STRUCTURE AND FUNCTIONS OF AN ity to using resources carefully has produced ECOSYSTEM societies that nature can no longer sustain. If one thinks before wasting resources such as wa- Structural aspects ter, reusing and recycling paper, using less plas- tics that are non-degradable, culminatively this Components that make up the structural as- can have positive implications on the integrity pects of an ecosystem include: of our natural resource base and conserve the resources that nature provides. 1) Inorganic aspects – C, N, CO2, H2O. Ecosystems and man: Every region of our earth 2) Organic compounds – Protein, Carbo- has different ecosystems based on its climatic hydrates, Lipids – link abiotic to biotic conditions and geographical feature. There are aspects. terrestrial ecosystems on land and aquatic eco- systems in water. 3) Climatic regimes – Temperature, Mois- ture, Light & Topography. 3.1.3 Resource utilisation 4) Producers – Plants. Most traditional societies used their environment 5) Macro consumers – Phagotrophs – Large sustainably. Though inequality in resource utili- animals.