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ECOSYSTEM-structure and function Biotic and abiotic components. Vertical distribution of different species occupying different levels is called stratification. The components of the ecosystem are seen to function as a unit when we consider (1) productivity (2) decomposition (3) energy flow (4) nutrient cycling. Productivity:- The rate of biomass production is called productivity. It is expressed in terms of g yr . -2 -1 PRIMARY PRODUCTIVITY • P P is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is measured in terms of weight g-2 or energy kcal m-2. • Productivity is divided into- Gross p p :- is the rate of production of organic matter during photosynthesis. Net p p:-GPP minus respiration losses is the NPP. GPP-R=NPP. • Secondary productivity:- The rate of formation of new organic matter by consumers. • Annual NPP of biosphere is 170 billion tons, productivity of oceans is only 55 billion tons. DECOMPOSITION • The process of break down of complex organic matter into inorganic substances like CO2 , H2O and nutrients is called decomposition. • Detritus:- dead plant remains such as leaves, bark, flowers, dead remains of animals including fecal matter. Various steps of decomposition are; • Fragmentation: Process of break down of detritus into smaller particles by detritivores (earthworm). • Leaching: water soluble inorganic nutrients go down into the soil horizon and get precipated as unavailable salts. Catabolism: • Process of degradation of detritus into simpler inorganic substances by bacterial and fungal enzymes. • Humification: leads to accumulation of a dark coloured amorphous substance called humus. • Humus is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. • Mineralisation: Humus is further degraded by some microbes and release of inorganic nutrients occur. Decomposition • It is an oxygen requiring process. The rate of decomposition is controlled by chemical composition of detritus and climatic factors. • Decomposition rate is slower if the detritus is rich in lignin and chitin, and quicker if detritus is rich in nitrogen and water-soluble substances like sugars. • Temperature and moisture are the climatic factors that regulate decomposition. Warm and moist environment favour decomposition. Low temperature and anaerobiosis inhibit decomposition. ENERGY FLOW • Of the incident solar radiation less than 50 per cent is photosynthetically active radiation (PAR). Plants capture only 2-10 per cent of the PAR. Energy flow is unidirectional from sun to producers to consumers. • Producers: • Consumers: primary consumer or herbivores, secondary consumer or primary carnivores, tertiary consumer or secondary carnivore. • Grazing food chain: Grass Goat Man. Detritus food chain • It begins with dead organic matter. It is made up of decomposers mainly fungi and bacteria (saprotrophs). Decomposers secrete digestive enzymes that breakdown dead and waste materials into simple inorganic materials which are absorbed by them. • In aquatic ecosystem GFC is the major conduit of energy flow. • In terrestrial ecosystem larger fraction of energy flows through DFC than GFC. • FOOD WEB: Trophic level • Specific place in the food chain. First , seond, third trophic level. The amount of energy decreases at each trophic level. • Standing crop: each trophic level has a certain mass of living material at a particular time. The standing crop is measured as the mass of living organisms (biomass), or the number in a unit area. • 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. Ecological pyramids • Pyramid of number, biomass, energy.- always upright. • Inverted pyramid: small standing crop of phytoplankton supports large standing crop of zooplankton.(biomass) • Limitations: it does not take into account the same species belonging to two or more trophic levels. It does not accommodate a food web . Saprophytes are not given any place in ecological pyramids. Ecological succession • The gradual and fairly predictable change in the species composition of a given area is E S. • These changes lead finally to a community that is in near equilibrium with the environment and is called a climax community. • The entire sequence of communities that successively change in a given area are called sere. • The individual transitional communities are termed seral stages or seral communities. • Primary succession: that starts where no living organisms are there. Eg:- bare rock, newly cooled lava, newly created pond or reservoir. Secondary succession • It begins in areas where natural biotic communities have been destroyed such as in abandoned farm lands, burned or cut forests, lands that have been flooded. • Hydrarch succession takes place in wetter areas and the successional series progress from hydric to the mesic conditions. • Xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions. • The species that invade a bare area are called pioneer species. In pri. Succ. On rocks- lichens bryophytes, bigger plants, climax forest. In pri. Succ. In waterphytoplankton's, free floating angiosperms, rooted hydrophytes, sedges, grasses, trees, climax forest. Nutrient cycling • The movement of nutrient elements through various components of an ecosystem is called nutrient cycling or biogeochemical cycle. • The amount of nutrients such as nitrogen, carbon, phosphorus, calcium, etc; present in the soil at any given time is referred to as the standing state. • Two types- gaseous (nitrogen, carbon), sedimentary (sulphur, phosphorus). Ecosystem services • The products of ecosystem processes are named as ecosystem services. Eg:-healthy forest ecosystem purify air and water, cycle nutrients, generate fertile soil provide wildlife habitat, pollinate crops, maintain biodiversity provide aesthetic, cultural, spiritual values. • Robert Constanza tried to put price tag on nature’s life support services.