Environment and Ecology

ENVIRONMENT AND ECOLOGY SYLLABUS Prelims: General issues on Environmental Ecology, Bio-diversity and Climate Change – that do not require subject specialization. Mains: GS Paper 3: Conservation, environmental pollution and degradation, environmental impact assessment TOPICS BASED ON PREVIOUS QUESTIONS Basic Concepts of Ecology Endangered Fauna National Parks, Sanctuaries, Reserves etc. International Conventions Legislation associated with conservation Conservation organisations Reports BIOSPHERE AND WORKING OF ECOSYSTEMS Biosphere Biosphere is that part of lithosphere, hydrosphere and atmosphere where plants and animals live. Biosphere contains all life forms on earth. The biosphere consists of - 1. all the living organisms (the biotic component), 2. energy and physical environment (the abiotic component) There are continuous interactions between living organisms and physical environment and among the living organisms themselves. BIOSPHERE BIOSPHERE The biosphere consists of two major systems viz. (i) terrestrial biomes systems (ii) aquatic biomes systems. The terrestrial biomes systems are further comprised of three subsystems viz., (i) plant system, (ii) animal system and (iii) soil system. These subsystems are intimately interrelated among themselves through the cyclic pathways of movements and transfer of energy and materials. BIOSPHERE The aquatic biomes systems are also composed of three sub-systems viz. : (i) Plant system, (ii) Animal system, (iii) Nutrients. These three sub-systems of aquatic biomes system of the biosphere are also intimately interrelated through cyclic pathways of movements of energy and matter among themselves. ECOLOGY Ecology can be defined as a scientific study of the interactions of organisms with their physical environment and with each other. The term ecology is derived from the Greek word ‘oikos’ meaning ‘house’, combined with the word ‘logy’ meaning the ‘science of’ or ‘the study of ’. Literally, ecology is the study of the earth as a ‘household’, of plants, human beings, animals and micro-organisms. A German zoologist Ernst Haeckel, who used the term as ‘oekologie’ in 1869, became the first person to use the term ‘ecology’. The study of interactions between life forms (biotic) and the physical environment (abiotic) is the science of ecology. ECOSYSTEM An ecosystem is a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment. COMPONENTS OF ECOSYSTEM There are four basic components of an ecosystem – 1. The abiotic part, which is the non-living environment. 2. The producers or autotrophs, the green plants capable of producing their own food by using the energy of sunlight to make carbohydrates from water and carbon dioxide; this process is called photosynthesis. 3. There are the consumers or heterotrophs. These are animals which obtain their food by eating plants or other animals. The heterotrophs in any ecosystem can be divided into groups by their feeding habits: COMPONENTS OF ECOSYSTEM i. Herbivores eat only living plant material; ii. Detritivores feed on dead plant and animal material; (millipedes, earthworms, sea cucumbers.) i. Carnivores eat other animals; ii. Omnivores eat both plant and animal material. 4. Decomposers, such as the bacteria and fungi that promote decay. Note: Detritivores are somewhat a branch of decomposers. The decomposers can either be classified into two groups: bacteria & fungi and detritivores. Scavengers are typically not thought to be detritivores, as they generally eat large quantities of dead organic matter TYPES OF ECOSYSTEM Terrestrial Ecosystem The ecosystem which is found only on landforms. The main factor which differentiates the terrestrial ecosystems from the aquatic ecosystems is the relative shortage of water in the terrestrial ecosystems and as a result the importance that water attains in these ecosystems due to its limited availability. Another factor is the better availability of light in these ecosystems as the environment is a lot cleaner in land than it is in water. The main types of terrestrial ecosystems are the forest ecosystems, the desert ecosystems, the grassland ecosystems and the mountain ecosystems. Aquatic Ecosystem An ecosystem which exists in a body of water. The aquatic ecosystems are mainly of two types, the freshwater ecosystems and the marine ecosystems. ENERGY FLOW IN ECOSYSTEM Sun is the primary source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR). PAR refers to the solar radiation that photosynthetic organisms are able to use in the process of photosynthesis. Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world. The energy of sunlight fixed in food production by green plants is passed through the ecosystem by food chains and webs from one trophic level to the next. In this way, energy flows through the ecosystem. THE TROPHIC STRUCTURE OF ECOSYSTEMS The organisation and pattern of feeding in an ecosystem is known as the trophic structure. The levels through which food energy passes from one group of organism to the other group are called trophic levels. FOOD CHAIN The chain of transformation and transfer of food energy in the ecosystem from one group of organism to another group through a series of steps or levels is called food chain. Two types of food-chains are recognised: 1. Grazing food-chain 2. Detritus food chain GRAZING FOOD-CHAIN In a grazing food-chain, the first level starts with plants as producers and ends with carnivores as consumers at the last level, with the herbivores being at the intermediate level. There is a loss of energy at each level which may be through respiration, excretion or decomposition. The trophic levels involved in a food chain range from 3 to 5 and energy is lost at each level. DETRITUS FOOD CHAIN This type of food chain goes from dead organic matter into microorganisms and then to organisms feeding on detritus (detrivores) and their predators. Such ecosystems are thus less dependent on direct solar energy. These depend chiefly on the influx of organic matter produced in another system. DETRITUS FOOD CHAIN FOOD WEB When the feeding relationship in a natural ecosystem become more complicated, the food chain does not remain simple and linear rather it is also complicated by several inter-connected overlapping food chains. This happens when greater number of species feed on many kinds of prey. Such complicated food chain is called food web. ENERGY FLOW IN ECOSYSTEM Energy is passed through the system in food chains and webs. The flow of energy in ecosystems is unidirectional. The important point to note is that the amount of energy decreases at successive trophic levels. The number of trophic levels in the grazing food chain is restricted as the transfer of energy follows 10 per cent law – only 10 per cent of the energy is transferred to each trophic level from the lower trophic level. Storage of energy in the system is shown by the amount of living material in both the plants and animals present. ENERGY FLOW IN ECOSYSTEM The amount of living material present is called the standing crop. This can be expressed in several ways but is usually shown as biomass (living material) per unit area, measured as dry weight, ash weight or calorific value. Usually the amount of standing crop in each trophic level decreases with each step on the food chain away from the plants. This can be shown diagrammatically by Ecological pyramids. ECOLOGICAL PYRAMID It is a graphical representation designed to show the biomass, bio productivity or the number of organisms at each trophic level in a given ecosystem. The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer. The three ecological pyramids that are usually studied are: 1. pyramid of numbers 2. pyramid of biomass 3. pyramid of energy. PYRAMID OF NUMBERS Pyramid of Numbers is the pyramid formed by the number of species present from one trophic level to higher trophic levels. The population of each organism in a food chain can be shown in a sort of bar chart called as pyramid of numbers. The more organisms there are, the wider the bar. The producer in the food chain always goes at the bottom of the pyramid of numbers. PYRAMID OF NUMBERS PYRAMID OF BIOMASS Biomass pyramid includes the total weight of the organic matter (total biomass) of each trophic level. Biomass is the mass of living material in each organism multiplied by the total number of organisms in that trophic level. Pyramids of biomass usually are a true pyramid shape (each level is smaller than the one below it). The biomass in each trophic level is always less than the trophic level below. PYRAMID OF BIOMASS PYRAMID OF ENERGY Energy Pyramid is the pyramid representing total amount of energy present at each trophic level of food chain in a natural ecosystem per unit area per unit time. The energy is expressed in kilocalories per square meter per day or per year. (Kcal/m2/day or year) An energy pyramid’s shape shows how the amount of useful energy that enters each level — chemical energy in the form of food — decreases as it is used by the organisms in that level. The energy that enters a community is ultimately lost to the living world as heat. PYRAMID OF ENERGY INFERENCES A given organism may occupy more than one trophic level simultaneously. For example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms. In most ecosystems, all the pyramids of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than at a higher level.

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