Unit 2 Ecosystem PDF

## 3.1 Concept of An Ecosystem * An ecosystem is a region with a specific landscape like forest, grassland, desert, wetland, or coastal area. * The nature of the ecosystem is based on its geographical features, such as hills, mountains, plains, rivers, lakes, coastal areas, or islands. * It is al...

## 3.1 Concept of An Ecosystem * An ecosystem is a region with a specific landscape like forest, grassland, desert, wetland, or coastal area. * The nature of the ecosystem is based on its geographical features, such as hills, mountains, plains, rivers, lakes, coastal areas, or islands. * It is also controlled by climatic conditions like the amount of sunlight, temperature, and rainfall. * The geographical, climatic, and characteristics form the non-living or abiotic component. * These features create conditions that support a community of plants and animals that have evolved to live in these specific conditions. The living component of the ecosystem is referred to as the biotic component. * Ecosystems are divided into terrestrial or land-based ecosystems and aquatic ecosystems in water. * These form the two major habitat conditions for Earth's living organisms. ### 3.1.1 Understanding Ecosystems * **Natural ecosystems** include forests, grasslands, deserts, and aquatic ecosystems like ponds, rivers, lakes, and the sea. * **Man-modified ecosystems** include agricultural land and urban or industrial land use patterns. **Common features of an ecosystem:** * **What does the ecosystem look like?** - Describe specific features of the different ecosystems in one's surroundings. * **What is its structure?** - Is it a forest, grassland, water body, agricultural area, grazing area, urban area, industrial area, etc.? * **What is the composition of its plant and animal species?** - List the well-known plants and animals you can see and document their abundance and numbers in nature. * **How does the ecosystem work?** - Observe and document the components of the ecosystem, which consist of its non-living or abiotic features such as air, water, climate, and soil. Its biotic components, the various plants and animals. Both these aspects of the ecosystem interact with each other. Plants, herbivores, and carnivores can be seen to form food chains. These chains are joined together to form a web of life on which man depends. ### 3.1.2 Ecosystem Degradation * Ecosystems are the basis of life itself! * The natural ecosystems in the wilderness provide a variety of products and are regions in which a number of vital ecological processes are present, without which human civilization would not be able to exist. * Ecosystems are frequently disrupted by human actions, which lead to the extinction of species of plants and animals that can live only in the different natural ecosystems. * Some species, if eliminated, seriously affect the ecosystem; these are called 'keystone' species. Exctinction occurs due to changes in land use. - Forests are deforested for timber, wetlands are drained to create more agricultural land, semi-arid grasslands that are used as pastures are changed into irrigated fields. * Pollution from industry and waste from urban settings can also lead to extinction of several species. * 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 and waste a very large proportion of resources and energy. * Increasing extraction of resources is at the cost of natural ecosystems, leading to a derangement of their important functions. ### 3.1.3 Resource Utilisation * Most traditional societies used their environment sustainably. * Though inequality in resource utilization has existed in every society, the number of individuals that used a large proportion of resources was extremely limited. In recent times, the proportion of 'rich' people in affluent societies grew rapidly. * Inequality thus became a serious problem. * Whereas in the past, many resources such as timber and fuel wood from the forest were extracted sustainably, this pattern has drastically changed during the last century. * The economically better-off sections began to use greater amounts of forest products, while those people who lived in the forest became increasingly poor. * Similarly, the building of large irrigation projects led to wealth in those areas that had canals, while those who had to remain dependent on a constant supply of water from the river itself, found it difficult to survive. * The key to this issue is the need for an 'equitable' distribution of all types of natural resources. A more even sharing of resources within the community can reduce these pressures on the natural ecosystems. ## 3.2 Structure and Functions of an Ecosystem **Structural aspects:** 1. **Inorganic aspects** - C, N, CO₂, H₂O 2. **Organic compounds** - Protein, Carbohydrates, Lipids - link abiotic to biotic aspects. 3. **Climatic regimes** - Temperature, Moisture, Light & Topography 4. **Producers** - Plants 5. **Macro consumers** - Phagotrophs - Large animals. 6. **Micro consumers** - Saprotrophs, absorbers - fungi. **Functional aspects:** 1. **Energy cycles** 2. **Food chains** 3. **Diversity - interlinkages between organisms.** 4. **Nutrient cycles - biogeochemical cycles.** 5. **Evolution** * Since each ecosystem has a non-living and a living part that are linked to each other, one needs to look around us and observe this closely. This is an important aspect that is a vital part of our lives. * The non-living components of an ecosystem are the amount of water, the various inorganic substances and organic compounds and climatic conditions such as rainfall and temperature, which depend on geographical conditions and location, which is also related to the amount of sunlight. The living organisms in an ecosystem are inseparable from their habitat. ### 3.3 Producers, Consumers, and Decomposers * **Producers** - Plants are the 'producers' in the ecosystem as they manufacture their food by using energy from the sun. * **Herbivores** - The herbivorous animals are primary consumers, as they live on the producers. * **Carnivores** - At a higher trophic level, there are carnivorous animals, or secondary consumers, which live on herbivorous animals. * **Decomposers** - Decomposers or detrivores are a group of organisms consisting of small animals like worms, insects, bacteria and fungi, which break down dead organic material into smaller particles and finally into simpler substances that are used by plants as nutrition. Decomposition thus is a vital function in nature, as without this, all the nutrients would be tied up in dead matter and no new life could be produced. * Most ecosystems are highly complex and consist of an extremely large number of individuals of a wide variety of species. * In the species-rich tropical ecosystems (such as in our country), only a few species are very common, while most species have relatively few individuals. Some species of plants and animals are extremely rare and may occur only at a few locations. These are said to be 'endemic' to these areas. * When human activities alter the balance in these ecosystems, the "perturbation" leads to the disappearance of these uncommon species. When this happens to an endemic species that is not widely distributed, it becomes extinct for all time. ### 3.4 Energy Flow In the Ecosystem * Every ecosystem has several interrelated mechanisms that affect human life. These are the water cycle, the carbon cycle, the oxygen cycle, the nitrogen cycle and the energy cycle. * While every ecosystem is controlled by these cycles, in each ecosystem its abiotic and biotic features are distinct from each other. * All the functions of the ecosystem are in some way related to the growth and regeneration of its plant and animal species. **Cycles:** * **Water Cycle:** The water cycle depends on the rainfall, which is necessary for plants and animals to live. * **Carbon Cycle:** Carbon is essential for the growth and development of plants and animals. Plants release oxygen into the atmosphere on which animals depend for their respiration. Plants therefore help in regulating and monitoring the percentage of Oxygen and Carbon dioxide in the earth's atmosphere. All of mankind thus depends on the oxygen generated through this cycle. It also keeps the CO₂ at acceptable levels. * **Oxygen Cycle:** Oxygen is taken up by plants and animals from the air during respiration. The plants return oxygen to the atmosphere during photosynthesis. This links the Oxygen Cycle to the Carbon Cycle. Deforestation is likely to gradually reduce the oxygen levels in our atmosphere. * **Nitrogen Cycle:** Nitrogen fixing bacteria and fungi in soil gives this important element to plants which absorb it as nitrates. The nitrates are a part of the plant's metabolism, which help in forming new plant proteins. * **Energy Cycle:** The energy cycle is based on the flow of energy through the ecosystem. Energy from sunlight is converted by plants themselves into growing new plant material which includes leaves, flowers, fruit, branches, trunks and roots of plants ### 3.6 Food Chains, Food Webs, and Ecological Pyramids * The transfer of energy from the source in plants through a series of organisms by eating and being eaten constitutes food chains. * At each transfer, a large proportion of energy is lost in the form of heat. * These food chains are not isolated sequences, but are interconnected with each other. This interlocking pattern is known as the food web. * Each step of the food web is called a trophic level. Hence green plants occupy the first level, herbivores the second level, carnivores the third level and secondary carnivores the fourth level. These trophic levels together form the ecological pyramid. **Food Chains and Webs:** * The most obvious aspect of nature is that energy must pass from one living organism to another. When herbivorous animals feed on plants, energy is transferred from plants to animals. In an ecosystem, some of the animals feed on other living organisms, while some feed on dead organic matter. * The latter form the 'detritus' food chain. At each linkage in the chain, a major part of the energy from the food is lost for daily activities. * Each chain usually has only four to five such links. However a single species may be linked to a large number of species. **Ecological Pyramids:** * In an ecosystem, green plants - the producers, utilize energy directly from sunlight and convert it into matter. A large number of these organisms form the most basic, or first 'trophic level' of the food pyramid. * The herbivorous animals that eat plants are at the second trophic level and are called primary consumers. * The predators that feed on them form the third trophic level and are known as secondary consumers. * Only a few animals form the third trophic level consisting of carnivores at the apex of the food pyramid. This is how energy is used by living creatures and flows through the ecosystem from its base to the apex. Much of the energy is used up in activities of each living organism.