Understanding the Environment 2024 PDF

Environmental Science & Education Unit 1: Understanding the Environment 1.1 Environment: concept, importance and components 1.2. Ecosystem: Concept, structure and function (food chain, food web, ecological pyramids and energy flow) 1.3. Ecosystem services: (Provisioning, regulating and cultural)...

Environmental Science & Education Unit 1: Understanding the Environment 1.1 Environment: concept, importance and components 1.2. Ecosystem: Concept, structure and function (food chain, food web, ecological pyramids and energy flow) 1.3. Ecosystem services: (Provisioning, regulating and cultural) 1.4. Biodiversity: levels, values and threats and conservation 1.5. Concept and objectives of environmental education, environmental ethics  Environmental Science & Education Unit 2: Natural resources and Environmental pollution 2.1. Natural resources: Renewable and non-renewable (Global status, distribution and production) 2.2. Management of natural resources: Individual, community and government managed 2.3. Air, water and soil pollution: Causes, consequences and control 2.4. Solid waste management: Collection, segregation, transportation and disposal; 3R's 2.5. Climate change: Causes and consequences Suggested Reading: Asthana, D. K. Text Book of Environmental Studies. S. Chand Publishing. Basu, M., Xavier, S. Fundamentals of Environmental Studies, Cambridge University Press, India. Basu, R. |1., (Ed.) Environment. University of Calcutta, Kolkata. Bharucha, E. Textbook of Environmental Studies for Undergraduate Courses. Universities Press. Miller T. Cr. Jr., Environmental Science, Wadsworth Publishing Co. Wagner K.D. Environmental Management. W.B. Saunders Co. Philadelphia, USA 499p. Mckinncv, M.L. & Schoch. R.M. Environmental Science systems & Solutions. Web enhanced edttion' 639p. Environment: concept, importance and components The word ‘Environment’ is derived from the French word ‘Environner’ which means to encircle, around or surround. The biologist Jacob Van Uerkal (1864-1944) introduced the term ‘environment’ in Ecology. Environment is defined as, “the sum total of living and non-living components; influences and events surrounding an organism”. As given by Environment Protection Act 1986, Environment is the sum total of land, water, air, interrelationships among themselves and also with the human beings and other living organisms. Environment: concept, importance and components Ecology is the study of the interactions of organisms with each other and their environment. Environmental Science is interdisciplinary field and requires the study of the interactions among the physical, chemical and biological components of the environment with a focus on environmental pollution and degradation. This means that it requires the knowledge of various other subjects including biology, chemistry, physics, statistics, microbiology, biochemistry, geology, economics, law, sociology, etc. The narrow definition of environmental science is the study of the human impact on the physical and biological environment of an organism. Types of environment based on the human interference: Natural Environment: is inherent, unaltered and not manipulated by man. Life processes and evolution processes are unhindered in such an environment. However, one does not often find such places in the present day. Core areas of biosphere reserve are examples of such environment. Other examples, Oceans, lakes/ponds, rivers, forest, grasslands, deserts etc. Human-modified Environment: A natural environment that is modified partially by human intervention. For examples, Orchards, plantations, sanctuaries, parks, etc. Human-made Environment: When natural environment is deliberately controlled and converted by man kind. For examples, Industries, cities, towns, crop fields, artificial lakes, dams, etc. COMPONENTS OF ENVIRONMENT The environment is composed of the following three main components. Abiotic components: light, humidity and water, temperature, atmospheric gases, altitude, latitude, and seasonal changes. Biotic components: plants (flora), animals (fauna) (including human beings), parasites, and microorganisms. Energy components: solar energy, geothermal energy, water energy, and nuclear energy. SEGMENTS OF THE ENVIRONMENT The four basic segments of environment are (1) atmosphere, (2) hydrosphere, (3) lithosphere, and (4) biosphere. Structure of the atmosphere The cover of air that envelops the earth is known as the atmosphere. The atmosphere is normally composed of 79 percent nitrogen, 20 percent oxygen and one percent as a mixture of carbon dioxide, water vapour and trace amounts of several other gases such as neon, helium, methane, krypton, hydrogen and xenon. The general structure of the atmosphere has several important features that have relevance to environmental problems. The atmosphere is divided into several layers: troposphere, stratosphere, mesosphere, thermosphere and exosphere Structure of the atmosphere-Troposphere The innermost layer The troposphere extends 17 kilometers above sea level at the equator and about 8 kilometers over the poles. It contains about 75 percent of the mass of the earth’s air. Temperature declines with altitude in the troposphere. All weather occurs in this layer. At the top of the troposphere temperatures abruptly begin to rise. The boundary where this temperature reversal occurs is called the tropopause. Tropopause is the boundary between the stratosphere and troposphere. Structure of the atmosphere-Stratosphere The stratosphere extends from 17 to 48 kilometers above the earth’s surface. While the composition of the stratosphere is similar to that of the troposphere it has two major differences. The volume of water vapour here is about 1000 times less while the volume of ozone is about 1000 times greater. This layer does not have clouds and hence airplanes fly in this layer as it creates less turbulence. Temperature rises with altitude in the stratosphere until there is another reversal. This point is called the stratopause and it marks the end of the stratosphere and the beginning of the atmosphere’s next layer, the mesosphere. Structure of the atmosphere-Mesosphere It extends from about 50 to 85 km above our planet. In the mesosphere the temperature decreases with altitude falling up to –110oC at the top. The boundary between the mesosphere and the thermosphere above is called the mesopause. Structure of the atmosphere-Thermosphere: It extends from about 90 km to between 500 and 1,000 km above our planet. In this layer, ionization of the gases is a major phenomenon, thus increasing the temperature. The temperatures can rise to 1,500 degrees Celsius, but it would not feel warm because of the low air pressure in this layer. The International Space Station orbits Earth in this layer. The boundary between the thermosphere and the exosphere above it is called the thermopause. Structure of the atmosphere-Exosphere: It is the outermost layer of Earth’s atmosphere. This layer separates the rest of the atmosphere from outer space. It starts at an altitude of about 500 km and goes out to about 10,000 km. Only the lower troposphere is routinely involved in our weather and hence air pollution. The other layers are not significant in determining the level of air pollution. The vital roles played by atmosphere in the survival of life in this planet. The atmosphere is the protective blanket of gases which is surrounding the earth. It protects the earth from the hostile environment of outer space. It absorbs IR radiations emitted by the sun and reemitted from the earth and thus controls the temperature of the earth. It allows transmission of significant amounts of radiation only in the regions of 300 – 2500 nm (near UV, Visible, and near IR) and 0.01 – 40 meters (radio waves). i.e it filters tissue damaging UV radiation below 300 nm. It acts as a source for CO2 for plant photosynthesis and O2 for respiration It acts as a source for nitrogen for nitrogen-fixing bacteria and ammonia producing plants. It creates the pressure without which liquid water couldn’t exist on our planet’s surface. The atmosphere transports water from ocean to land. Hydrosphere A hydrosphere is the total amount of water on a planet. The hydrosphere includes water that is on the surface of the planet, underground, and in the air. Water is the essential element that makes life on earth possible. Without water there would be no life. Hydrosphere Although 71% of the earth’s surface is covered by water only a tiny fraction of this water is available to us as fresh water. About 97% of the total water available on earth is found in oceans and is too salty for drinking or irrigation. The remaining 3% is fresh water. Slightly more than 2% is locked in ice caps or glaciers. Less than 0.03% of the earth’ total volume of water is available in lakes, streams, rivers and wetlands. The groundwater and soil water make up about 0.63% and 0.005% of fresh water respectively. This makes water a very precious resource. The future wars in our world may well be fought over water. Lithosphere The lithosphere began as a hot ball of matter which formed the earth about 4.6 billion years ago. About 3.2 billion years ago, the earth cooled down considerably and a very special event took place - life began on our planet. Lithosphere is the rigid, rocky outer layer of the Earth, consisting of the crust and the solid outermost layer of the upper mantle. It extends to a depth of about 60 miles (100 km). The Earth's Crust is very thin in comparison to the other three layers. The crust is only about 3-5 miles (8 kilometers) thick under the oceans (oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust). Lithosphere There are two types of lithosphere: Oceanic lithosphere- which is associated with oceanic crust and exists in the ocean basins. Continental lithosphere- which is associated with continental crust. The lithosphere includes a various number of different landforms such as mountains, valleys, rocks, minerals and soil. The lithosphere is constantly changing due to forces and pressures such as the sun, wind, ice, water and chemical changes. Biosphere The part of the earth’s surface and the atmosphere in which plants and animals live is called biosphere. It comprises lithosphere, hydrosphere, and atmosphere. Biosphere is relatively thin life-supporting stratum of Earth’s surface, extending from a few kilometers into the atmosphere to the deep-sea vents of the ocean. The main components of the environment are interconnected by two factors – a) the one-way flow of energy from the sun, through the living organisms in their feeding interactions, into the environment, and eventually to outer space as heat. As the solar energy interacts with carbon dioxide and other gases in the troposphere, it warms the earth surface and lower atmosphere by the process of greenhouse effect. The later makes the earth’s temperature sustainable for living organisms which would otherwise be too cold to support the life on earth. b) the cycling of the nutrients through parts of biosphere. The nutrients that cycle through the major biogeochemical cycles are carbon, oxygen, hydrogen, nitrogen, phosphorous and sulphur – all of which are essential for life. These biogeochemical cycles operate at global scale and involve all of the main components of environment, thus materials are transferred continually between the lithosphere, atmosphere, hydrosphere and biosphere. 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. Ecosystem: Concept, structure and function (food chain, food web, ecological pyramids and energy flow) Ecosystem services: (Provisioning, regulating and cultural) Ecology and Ecosystem Ecology is the study of the interactions of organisms with each other and their environment. The term Ecology was coined by Earnst Haeckel in 1869. It is derived from the Greek words Oikos- home + logos- study. Population: all of the organisms of the same species in the same place at the same time. Community: all populations in the same place at the same time (all living things). Ecosystem (ecological system)-The interactions of a community with the abiotic elements of a specific area. Ecosystem (ecological system)-is a region in which living organisms interact with their environment. Sir Arthur Tansley (1935): First time used the term “Ecosystem” Modern ecology is now defined as “the study of structure and functions of ecosystems.” CONCEPT OF AN ECOSYSTEM An ‘Ecosystem’ is a region with a specific and recognizable landscape form such as 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 such as the amount of sunlight, the temperature and the rainfall in the region. The geographical, climatic and soil characteristics form its non-living (abiotic) component. These features create conditions that support a community of plants and animals that evolution has produced to live in these specific conditions. The living part of the ecosystem is referred to as its biotic component. All the living organisms in an area live in communities of plants and animals. They interact with their non-living environment, and with each other at different points in time for a large number of reasons. CONCEPT OF AN ECOSYSTEM Life can exist only in a small proportion of the earth’s land, water and its atmosphere. At a global level the thin skin of the earth on the land, the sea and the air, forms the biosphere. At a sub-global level, this is divided into biogeographical realms, eg. Eurasia called the palaeartic realm; South and South-East Asia (of which India forms a major part) is the Oriental realm; North America is the Nearctic realm; South America forms the Neotropical realm; Africa the Ethiopian realm; and Australia the Australian realm. CONCEPT OF AN ECOSYSTEM At a national or state level, this forms biogeographic regions. There are several distinctive geographical regions in India- the Himalayas, the Gangetic Plains, the Highlands of Central India, the Western and Eastern Ghats, the semi-arid desert in the West, the Deccan Plateau, the Coastal Belts, and the Andaman and Nicobar Islands. These geographically distinctive areas have plants and animals that have been adapted to live in each of these regions. CONCEPT OF AN ECOSYSTEM At an even more local level, each area has several structurally and functionally identifiable ecosystems such as different types of forests, grasslands, river catchments, mangrove swamps in deltas, seashores, islands, etc. to give only a few examples. Here too each of these forms a habitat for specific plants and animals. Thus, the size of ecosystems varies tremendously. An ecosystem could be an entire rain forest, covering a large geographical area, or it could be a single tree inhabiting a large no. of birds and/or microorganisms in its leaf litter. It could be a termite’s gut, a lake or the biosphere as a whole with an entire intertwined environment of earth. The number of ecosystems on earth is countless and each ecosystem is distinct. Thus, ecosystems have both non-living and living components that are typical to an area giving it its own special characteristics that are easily observed. CONCEPT OF AN ECOSYSTEM Ecosystems have been formed on land and in the sea by evolution that has created species to live together in a specific region. Ecosystems are divided into terrestrial or land-based ecosystems, and aquatic ecosystems in water. These form the two major habitat conditions for the Earth’s living organisms. Ecosystems can be: Natural ecosystems include the forests, grasslands, deserts, and aquatic ecosystems such as ponds, rivers, lakes, and the sea. Man modified ecosystems include agricultural land and urban or industrial land use patterns. STRUCTURE AND FUNCTIONS OF AN ECOSYSTEM Structural aspects: This refers to all the elements that make up an ecosystem-the individuals and communities of plants and animals (biotic) as well as the non- living natural resources (abiotic) present in the ecosystems. Ecosystem structure is created due to interaction between abiotic and biotic components, varying over space and time. 1. Abiotic Components: The abiotic components of an ecosystem refer to the physical environment or the non-living factors. The organisms cannot live or survive without their abiotic components. They mainly include, inorganic substances, organic compounds, climatic factors, edaphic and other factors. 2. Biotic Components: The biotic components of the ecosystems are the living organisms including plants, animals and microorganisms. Based on their nutritional requirement, i.e. how they get their food, they are categorized into three groups, producers, consumers and decomposers. STRUCTURE AND FUNCTIONS OF AN ECOSYSTEM Structural aspects: Abiotic Components: They mainly include i) inorganic substances required by organisms such as carbon dioxide, water, nitrogen, calcium, phosphorus, etc. that are involved in material cycles. The amount of these inorganic substances present at any given time in ecosystem is called as standing state or standing quality of ecosystem. ii) organic compounds like proteins, carbohydrates, amino acids, lipids, humic substances and others are synthesized by the biotic counterpart of an ecosystem. They make biochemical structure of ecosystem. iii) climatic factors including mainly rain, light, temperature, humidity, wind and air and iv) Edaphic and other factors such as minerals, soil, topography, pH, etc. greatly determine the functions, distribution, structure, behavior and inter- relationship of organisms in a habitat. STRUCTURE AND FUNCTIONS OF AN ECOSYSTEM Structural aspects: 2. Biotic Components: Based on their nutritional requirement, i.e. how they get their food, they are categorized into three groups – i) Producers are mainly the green plants with chlorophyll which gives them the ability to use solar energy to manufacture their own food using simple inorganic abiotic substances, through the process of photosynthesis. They are also called as photoautotrophs (photo-light, auto-self, troph- nutrition). This group is mainly constituted by green plants, herbs, shrubs, trees, phytoplanktons, algae, mosses, etc. There are some chemosynthetic bacteria (sulphur bacteria) deep beneath in the ocean which can synthesize their food in absence of sunlight, thus known as chemoautotrophs (chemo-chemical, auto-self, troph-nutrition). STRUCTURE AND FUNCTIONS OF AN ECOSYSTEM Structural aspects: 2. Biotic Components: Based on their nutritional requirement, i.e. how they get their food, they are categorized into three groups – i) Consumers lack chlorophyll, so they depend on producers for food. They are also known as heterotrophs. They mainly include herbivorous (feed on plants), carnivorous (feed on other animals), omnivorous (feed on both plants and animals) and detritivores organisms (feed on dead parts, waste, remains, etc. of plants and animals,). ii) Decomposers (saprotrophs) are the microorganisms, bacteria and fungi, which break down complex dead organic matter into simple inorganic forms, absorb some of the decomposition products, and release inorganic nutrients that are reused by the producers. All ecosystems have their own set of producers, consumers and decomposers which are specific to that ecosystem. STRUCTURE AND FUNCTIONS OF AN ECOSYSTEM Functional aspects: Ecosystems exhibit a natural tendency to persist which has been made possible by a variety of functions performed by the structural components. ‘Functions’ refer to the biological, geochemical and physical processes that take place within an ecosystem. Ecosystems are thermodynamically open, which exhibit the exchange matter and energy with their environment. The key functional aspects of ecosystems are- 1) Energy flow. 2) Food chains and food webs 3) Nutrient cycles-biogeochemical cycles 4) Ecosystem development 5) Ecosystem regulation and stability ENERGY FLOW IN THE ECOSYSTEM Everything that organisms do in ecosystems (breathing, running, burrowing, growing) all require energy. So, how do they get it? In an ecosystem, there is a continuous interaction between plants, animals, and their environment to produce and exchange materials. The energy needed for this material cycling comes from the Sun. Sun is the ultimate source of energy, directly or indirectly, for all other forms. The green plants capture the solar energy and convert it through the process of photosynthesis into chemical energy of food (organic matter) and store it into their body. This process is called as primary production. The rate of total organic matter production by green plants (primary producers) is known as gross primary productivity. The green plants use some of the energy in the process of respiration. The rest amount of energy is called as net primary production, the amount of energy left for the heterotrophic organisms. In this stored form, other organisms take the energy and pass it on further to other organisms. During this process, a reasonable proportion of energy is lost out of the living system. At the consumer level, the rate of assimilation of energy is called secondary productivity. The whole process is called as flow of energy. ENERGY FLOW IN THE ECOSYSTEM Primary productivity of an ecosystem depends upon the solar radiations, availability of water, nutrients and upon the plants and their chlorophyll content. Productivity of tropical rainforest and estuaries is highest. The greater productivity of tropical rainforests to a large extent is due to the favorable combination of high incident solar radiation, warm temperatures, abundant rainfall, and rich diversity of species. These factors result into longer, almost year-round growing season. In estuaries, the natural wave currents bring lots of nutrients with them congenial for growth. On the other hand, desert ecosystems have limitations of adequate water supply while tundra ecosystems have low water temperature as limiting factor and hence show low primary production. The most important feature of the energy flow is one-way or unidirectional or non-cyclic flow. It flows from producer to herbivores to carnivores organisms; it is never reused back in the food chain unlike the nutrients which move in a cycle. As the flow of energy takes place, there is a gradual loss of energy at each level. Schematic diagram showing unidirectional flow of energy and nutrients cycling in an ecosystem. Ten percent (10%) Law of energy flow in an ecosystem: At each step up the food chain, only 10 percent of the energy is passed on to the next level, while approximately 90 percent of the energy is lost as heat. FOOD CHAINS, FOOD WEBS AND ECOLOGICAL PYRAMIDS The flow of energy in an Ecosystem is mediated through a series of feeding relationships in a definite sequence or pattern i.e. from producers to primary consumers to secondary consumers and to tertiary consumers. Nutrients too move in along this food chain. The sequence of eating and being eaten in an ecosystem is known as food chain. Grass → Grasshopper → Frog → Snake → Hawk (Grassland ecosystem) Plants → Deer → Lion (Forest ecosystem) Phytoplanktons → Zooplanktons → Small fish → Large fish (Pond ecosystem) FOOD CHAINS, FOOD WEBS AND ECOLOGICAL PYRAMIDS The food chains can be of two types – 1. Grazing food chain: The food chain that starts from green plants and ends in a consumer. Some examples are: Grass → Insect → Sparrow → Eagle Tree → Bird → Snake → Hawk Plants → Deer → Tiger Phytoplankton → Zooplankton → Small fish → Big fish → Human beings 2. Detritus food chain: In many cases, the principal energy input is not green plants but dead organic matter. These are called detritus food chains. The detritus food chains are commonly found in forest floors, salt marshes and the ocean floors in very deep areas. Example of detritus food chain is as follows: Leaf litter → Bacteria → Protozoa → Small fish → Large fish FOOD CHAINS, FOOD WEBS AND ECOLOGICAL PYRAMIDS These food chains are not isolated sequences, but are interconnected with each other. In an ecosystem there are a very large number of interlinked chains. This interlocking pattern is known as the food web. A food web consists of all the food chains in a single ecosystem. Each step of the food web is called a trophic level. These trophic levels together form the ecological pyramid. If the linkages in the chains that make up the web of life are disrupted due to human activities that lead to the loss or extinction of species, the web breaks down. https://www2.nau.edu/lrm22/lessons/food_chain/food_chain.html (Figure) FOOD CHAINS, FOOD WEBS AND ECOLOGICAL PYRAMIDS Each organism in the ecosystem is assigned a feeding level or trophic level depending on its nutritional status. Grass → Grasshopper → Frog → Snake → Hawk (Grassland ecosystem) Thus, in grassland food chain, Plants (Primary Producers) grass occupies 1st trophic Trophic Level (T 1) level, grasshopper the 2nd, frog Grass, plants, trees, shrubs, phytoplankton the 3rd, snake the 4th and hawk Herbivores (Primary Consumers) 5th trophic level. Trophic Level (T 2) In a food chain only around 10 Insects, Grasshopper, Deer, Giraffe percent of the energy is passed First order Carnivores (Secondary Consumers) on to the next trophic level. Trophic Level (T 3) Therefore, the number of Frog, Lizard, Crabs, Snake trophic levels in a food chain is Second order Carnivores (Tertiary Consumers) limited. Trophic Level (T 4) Eagle, Tigers, Sea otters, Crocodiles FOOD CHAINS, FOOD WEBS AND ECOLOGICAL PYRAMIDS Food webs give greater stability to an ecosystem due to their complexity. In a linear food chain, if one species become extinct or one species suffers, then the species in the subsequent trophic levels are also affected. In a food web, on the other hand, there are a number of options available at each trophic level. So if one species is affected, it does not affect other trophic levels so seriously. Keystone Species: In some food webs, there is one critical "keystone species" upon which the entire system depends. In the same way that an arch collapses when the keystone is removed, an entire food chain can collapse if there is a decline in a keystone species. Often, the keystone species is a predator that keeps the herbivores in check, and prevents them from overconsuming the plants, leading to a massive die off. When we remove top predators like grizzly bears, orca whales, or wolves, for example, there is evidence that it affects not just the prey species, but even the physical environment. Apex Predators: These species are at the top of the food chain and the healthy adults have no natural predators. ECOLOGICAL PYRAMIDS Ecological pyramids are the way to show the structure of ecosystems, the term was first described by Charles Elton in 1920s. They can also be called as trophic pyramids or energy pyramids. Ecological pyramids are graphical representations that show the relative amounts of various parameters (such as number of organisms, energy, and biomass) across trophic levels. Three types of ecological pyramids are generally described: 1) Pyramid of Numbers, in which individuals at each successive trophic level are counted per unit area and their numbers are plotted in the form of pyramids. 2) Pyramid of Biomass, in which the total biomass existing at each of the successive trophic levels is measured in terms of dry weight or caloric value, per unit area and plotted. 3) Pyramid of Energy, in which energy flow per unit time at each of the successive trophic levels is measured and plotted. It is also called as pyramids of productivity. ECOLOGICAL PYRAMIDS: Pyramid of Numbers: Pyramid of numbers may be defined as graphical representation of number of individual organisms per unit area at each trophic level arranged stepwise with producers at the base and top carnivores at the top. The shape of pyramid of numbers may vary from one ecosystem to another ecosystem.  In grassland and aquatic ecosystems, pyramid of number is upright. The producers in the grassland are the grasses and in aquatic ecosystems are phytoplanktons (algae etc.) which are small in size and large in number per unit area. So the producers form a broad base in the pyramid. The herbivores in the grassland are the insects; carnivores are frogs, birds, etc. and top carnivores are hawk, eagle, foxes etc. which are gradually less and less in number and so the pyramid apex becomes gradually narrower forming an upright and erect pyramid. Similar is the case with herbivores (zooplanktons, etc.), carnivores (small fishes, etc.) and top carnivores (large fishes, crocodile, etc.) in aquatic ecosystems (pond, lake or marine ecosystem) which decreases in number at higher Pyramid of Numbers in Grassland Ecosystem trophic levels, thus forming an upright pyramid of numbers. (Upright) ECOLOGICAL PYRAMIDS: Pyramid of Numbers: In a forest ecosystem, large sized trees are the producers, which are less in number and so form a narrow base. The trees support large number of herbivores like insects, birds, frogs, etc. including several species of animals that feed upon leaves, fruits, flowers, bark, etc. of the trees. They are large in number than trees and hence form a middle broad level. The secondary consumers like predatory birds (hawks, eagle, etc.), foxes, snakes, lizards, etc. are less in number than herbivores while top carnivores like lion, tiger, etc. are still smaller in number making the pyramid gradually narrow towards apex. So the pyramid assumes a spindle shape with narrow on both sides and broader in the middle. Pyramid of Numbers in Forest Ecosystem (Spindle shaped) ECOLOGICAL PYRAMIDS: Pyramid of Numbers: In a parasitic food chain, for example, the producers like a few big trees offers food to quite a lot of frugivorous birds which are the herbivores and more in number than trees. The birds harbor and sustain a good number of ecto-parasites like lice, bugs, etc., while a greater number of hyperparasites like bugs, fleas, microbes, etc. feed upon them. This when graphically represented form an inverted pyramid. Pyramid of Numbers in a Parasitic Food chain (Inverted) ECOLOGICAL PYRAMIDS: Pyramid of Biomass: A pyramid of biomass shows the relationship between biomass and trophic level by quantifying the biomass present at each trophic level at a particular time. It is a graphical representation of biomass (total amount of living organic matter in an ecosystem) present in unit area at a particular time in different tropic levels. The pyramid of biomass may be upright or inverted. For example, in a forest ecosystem, the plants and trees (primary producers) make up a large percentage of the biomass, with gradually lessening of biomass present at herbivores, carnivores and top carnivores level respectively per unit area at a particular time. Therefore, the pyramid of biomass in a forest ecosystem is upright with producers forming the broad base and consumers forming narrow top. ECOLOGICAL PYRAMIDS: Pyramid of Biomass: In contrast, in a pond ecosystem, the pyramid of biomass is inverted as the standing crop of phytoplanktons, the major producers, at any given time make up less biomass than the consumers, such as fishes and insects. As with inverted pyramids of numbers, the inverted biomass pyramid is not due to a lack of productivity from the primary producers, but results from the high turnover rate of the phytoplankton. The phytoplanktons are consumed rapidly by the primary consumers, which minimizes their biomass at any particular point in time. However, since phytoplanktons reproduce quickly, they are able to support the rest of the ecosystem. One problem with pyramids of biomass is that they can make a trophic level appear to contain more energy than it actually does. For example, all birds have beaks and skeletons, which despite having mass are not typically digested by the next trophic level. ECOLOGICAL PYRAMIDS: Pyramid of Energy: The pyramid of energy is by far the most practical of all the three ecological pyramids as it depicts the actual functional relationships between trophic levels. It represents the amount of energy present at each trophic level. Likewise it starts with the producers and ends with consumers at higher trophic levels. It is also called as pyramid of productivity. Since the productivity or energy flow is expressed per unit time basis, the pyramid is always and for all the ecosystems is an upright position. For ecosystem to be self sustaining, lower trophic levels should have more amount of energy than the higher trophic levels. This helps the organisms at lower levels to maintain a stable population, but also to transfer energy up the pyramid. ECOLOGICAL PYRAMIDS: Pyramid of Energy: As per the second law of thermodynamics, energy flow declines from producer level to successive trophic levels. When energy is transferred to next trophic levels, only about 10% of it is utilized to assemble body mass and become stored energy. Remaining 90% is lost in metabolic activities. This decline in energy at subsequent level is referred to as Lindeman’s data or 10% law. Therefore, pyramid of energy is always upright. ECOLOGICAL PYRAMIDS: Pyramid of Energy: The advantages of pyramid of energy are as follows: 1. It takes account of the rate of production over a period of time. 2. The shape of the pyramid of energy is not affected by size or rate of metabolism of organisms, while the other two pyramids (number and biomass) are affected by them. Animals may have larger biomass per unit area than plants, but their production per unit time per unit area would be smaller than the plants. 3. The energy content of two species bearing same mass or weight may be different; in such case biomass may be a misleading factor whereas energy is truly comparable. 4. In energy pyramids, the relative energy flow within an ecosystem can be compared and so also different ecosystem can be compared using energy pyramids. ECOLOGICAL PYRAMIDS: Pyramid of Energy: However, there are some disadvantages of pyramid of energy. Firstly, the rate of biomass production of an organism is required, which involves measuring growth and reproduction through time. Further, one organism can exist at two or more trophic level. So there is a difficulty while assigning the organisms to a specific trophic level. Also problem exists for assigning the decomposers or detritivores to a particular trophic level. In the nutshell, pyramids of energy are the most consistent and representative models of ecosystem structure in the study of energy flow through the ecosystem. CONCEPT OF AN ECOSYSTEM All ecosystems have the following common characteristics as given by Smith (1966): 1. The ecosystem is the major structural and functional unit of ecology. 2. The structure of an ecosystem is related to its species diversity; the more complex ecosystems have high species diversity. 3. The function of the ecosystem is related to energy flow and material cycling through and within the system. 4. The relative amount of energy needed to maintain an ecosystem depends on its structure. The more complex the structure, the lesser the energy it needs to maintain itself. 5. Ecosystems mature by passing from less complex to more complex stages. Early stages of such succession have an excess of potential energy and a relatively high energy flow per unit biomass. Later (mature) stages have less energy accumulation and its flow through more diverse components. 6. Both the environment and energy fixation in any given ecosystem are limited and cannot be exceeded without causing serious undesirable effects. 7. Alterations in the environment represent selective pressures upon the population to which it must adjust. Organisms which are unable to adjust to the changed environment disappear ultimately. Ecosystem services The specific ecosystem functions that are directly or indirectly beneficial to human beings are called ecosystem services. These functions provide life support services to humans and other species. According to Millennium Ecosystem Assessment (MEA), a major UN- sponsored effort to analyze the impact of human actions on ecosystems and human well-being, identified four major categories of ecosystem services: provisioning, regulating, cultural and supporting services. Ecosystem services 1. Provisioning services: are the material benefits people get from ecosystems for e.g. supply of food, water, fibers, wood and fuels. 2. Regulating services: are the benefits obtained from the regulation of ecosystem processes e.g. the regulation of air quality and soil fertility, climate regulation, control of floods or crop pollination. 3. Cultural services: These are the non-material benefits that people obtain from ecosystems such as spiritual enrichment, intellectual development, recreation and aesthetic values, tourism. 4. Supporting services: are necessary for the production of all other ecosystem services, for e.g. by providing plants and animals with living spaces, photosynthesis, nutrient cycling, the creation of soils, the water cycle, allowing for diversity of species, and maintaining genetic diversity. https://www.fao.org/ecosystem-services-biodiversity/en/ Ecosystem services Despite the ecological and economic importance of these services, ecosystems and the biodiversity are being degraded and lost at an unprecedented scale. One major reason for this is the value of ecosystems to human welfare are poorly understood and not fully recognized in every day planning and decision-making. In simplistic economic terms, the value of ecosystem services is larger than the global economy. Ecosystem services go beyond the direct economic benefits derived from exploitation of very specific ecosystem functions such as timber from forests. It is ecosystems ongoing capacities to provide a stream of life supporting and life enhancing services that are vital to human well being. Many of these services are non-market services by virtue of their inherent characteristics eg. both the atmospheric ozone layer, and the climate stability provided by the global carbon cycle, cannot be owned by anyone who can control their use by others. Furthermore, the costs of externalities of economic development (e.g. pollution, deforestation) are usually not accounted for, while inappropriate tax and subsidy (incentive) systems encourage the over-exploitation and unsustainable use of natural resources and other ecosystem services at the expense of the poor and future generations. Provisioning Services: These are the products obtained from ecosystems, including: Food and fiber. This includes the vast range of food products derived from plants, animals, and microbes, as well as materials such as wood, jute, hemp, silk, and many other products derived from ecosystems. Fuel. Wood, dung, and other biological materials serve as sources of energy. Genetic resources. This includes the genes and genetic information used for animal and plant breeding and biotechnology. Biochemicals, natural medicines, and pharmaceuticals. Many medicines, biocides, food additives such as alginates, and biological materials are derived from ecosystems. Ornamental resources. Animal products, such as skins and shells, and flowers are used as ornaments, although the value of these resources is often culturally determined. This is an example of linkages between the categories of ecosystem services. Fresh water. Fresh water is another example of linkages between categories—in this case, between provisioning and regulating services. Regulating Services: These are the benefits obtained from the regulation of ecosystem processes, including: Air quality maintenance. Ecosystems both contribute chemicals to and extract chemicals from the atmosphere, influencing many aspects of air quality. Climate regulation. Ecosystems influence climate both locally and globally. For example, at a local scale, changes in land cover can affect both temperature and precipitation. At the global scale, ecosystems play an important role in climate by either sequestering or emitting greenhouse gases. Water regulation. The timing and magnitude of runoff, flooding, and aquifer recharge can be strongly influenced by changes in land cover, including, in particular, alterations that change the water storage potential of the system, such as the conversion of wetlands or the replacement of forests with croplands or croplands with urban areas. Pollination. Ecosystem changes affect the distribution, abundance, and effectiveness of pollinators. Regulating Services: Water purification and waste treatment. Ecosystems can be a source of impurities in fresh water but also can help to filter out and decompose organic wastes introduced into inland waters and coastal and marine ecosystems. Regulation of human diseases. Changes in ecosystems can directly change the abundance of human pathogens, such as cholera, and can alter the abundance of disease vectors, such as mosquitoes. Biological control. Ecosystem changes affect the prevalence of crop and livestock pests and diseases. Erosion control. Vegetative cover plays an important role in soil retention and the prevention of landslides. Storm protection. The presence of coastal ecosystems such as mangroves and coral reefs can dramatically reduce the damage caused by hurricanes or large waves. Cultural Services: These are the nonmaterial benefits people obtain from ecosystems through spiritual enrichment, cognitive development, reflection, recreation, and aesthetic experiences, including: Cultural diversity. The diversity of ecosystems is one factor influencing the diversity of cultures. Spiritual and religious values. Many religions attach spiritual and religious values to ecosystems or their components. Knowledge systems (traditional and formal). Ecosystems influence the types of knowledge systems developed by different cultures. Educational values. Ecosystems and their components and processes provide the basis for both formal and informal education in many societies. Aesthetic values. Many people find beauty or aesthetic value in various aspects of ecosystems, as reflected in the support for parks, “scenic drives,” and the selection of housing locations. Cultural Services: Inspiration. Ecosystems provide a rich source of inspiration for art, folklore, national symbols, architecture, and advertising. Social relations. Ecosystems influence the types of social relations that are established in particular cultures. Fishing societies, for example, differ in many respects in their social relations from nomadic herding or agricultural societies. Sense of place. Many people value the “sense of place” that is associated with recognized features of their environment, including aspects of the ecosystem. Cultural heritage values. Many societies place high value on the maintenance of either historically important landscapes (“cultural landscapes”) or culturally significant species. Recreation and ecotourism. People often choose where to spend their leisure time based in part on the characteristics of the natural or cultivated landscapes in a particular area. Supporting Services Supporting services are those that are necessary for the production of all other ecosystem services. They differ from provisioning, regulating, and cultural services in that their impacts on people are either indirect or occur over a very long time, whereas changes in the other categories have relatively direct and short-term impacts on people. (Some services, like erosion control, can be categorized as both a supporting and a regulating service, depending on the time scale and immediacy of their impact on people.) For example, humans do not directly use soil formation services, although changes in this would indirectly affect people through the impact on the provisioning service of food production. Supporting Services Similarly, climate regulation is categorized as a regulating service since ecosystem changes can have an impact on local or global climate over time scales relevant to human decision-making (decades or centuries), whereas the production of oxygen gas (through photosynthesis) is categorized as a supporting service since any impacts on the concentration of oxygen in the atmosphere would only occur over an extremely long time. Some other examples of supporting services are primary production, production of atmospheric oxygen, soil formation and retention, nutrient cycling, water cycling, and provisioning of habitat.