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Note On Ecosystem

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Published in: Botany
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Types of ecosystems described include grassland , aquatic , primary succession , secondary succession, biogeochemical cycle and ecological services .

Dhanalakshmi L / Madurai

12 years of teaching experience

Qualification: M.Sc (University Of Madras , Chennai - 2006)

Teaches: Bio Technology, Biology, Botany, Home Science, Zoology, Bio Chemistry, Food Inspector Exam, Forest Department Exam

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  1. ECOSYSTEM 16 June 2022 17:29 British ecologist Arthur Tansley first defined the term Ecosystem. ECOSYSTEM :- the functional unit of nature, where living organisms interact among themselves and with the surrounding physical environment. Types of Ecosystems: Flow hart ofclassifica tion of ecos»tem Ecose"em ecosvsttm Forest Grassland tem ecossstem Desert 'Stem resh wat ecos stem Artificial ecosystem Aquatic Marine ecos stem New Species Discovered in Different Ecosystems: Pinocchio: long nosed frog found in Indonesia Bald headed parrot in Amazon Yeti Crab (Kiwa hirsuta) near Easter islands. Structure of Ecosystems An Ecosystem has two components: Biotic components and Abiotic components New Section I Page I
  2. Stratification: This is the Vertical Distribution of Different Species occupying Different Levels. The levels are called STRATA. For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers. Emergents canopy Shrub 't Major functional components of an ecosystem are: (a) Productivity (b) Decomposition (c) Energy flow (d) Nutrient cycling Aspects Affecting the Functioning of an Ecosystem are: 1. PRODUCTIVITY The rate of synthesis of organic matter (biomass) during a given period of time. It is measured as weight (g-2) or as energy (kcal m-2). It is used to compare productivity of different ecosystems. • Primary productivity: It is the amount of biomass produced per unit area in a given time period by Plants during Photosynthesis. New Section I Page 2
  3. GPP-R= NPP *GPP-Gross Primary Productivity • Secondary productivity *NPP-Net Primary Productivity It is the amount of biomass produced at any of the Consumer levels in a given period of time. 2. DECOMPOSITION It is the process of breaking down of dead organic matter into smaller organic molecules and inorganic molecules by Decomposers (bacteria, fungi) DETRITUS: Dead remains of plants and animals is called detritus. DETRITIVORES: Animals that feed on decaying organic matter (detritus). Examples: earthworms, termites, snails etc New Section I Page 3
  4. A tree grows in the soil Some are eaten by insects and other animals. Nutrients and enerOr enter food web. A green leaf falls to the ground Leaves partially consumed by decomposers such as fungi and bacteria. They begin to lose form and become litter. Further decomposition by earthworms , bacteria, soil,mites,fun ,etc. Organic rich soil Mechanism of Decomposition: Some nutrients leach into soil by chemical action 1. Fragmentation of Detritus: Detritivores feed on detritus ---breakdown -- increases the surface area of detritus particles for microbial action. 2. Leaching: Soluble inorganic nutrients dissolve in water -— percolate through the soil ---removed due to leaching action. 3. Catabolism: Decomposers (bacteria, fungi) release enzymes --- decompose detritus --- simpler inorganic compounds. 4. Humification: Simplified detritus--- converted to HUMUS - Humus is a Dark, Amorphous substance. - Highly resistant to Microbial Action - Undergoes Decomposition very Slowly. - Reservoir of nutrients (due to colloidal nature) 5. Mineralisation: Humus is degraded — releases inorganic substances ( C02, H20 etc) and nutrients (Ca2+, Mg2+,K+ etc) New Section I Page 4
  5. Factors affecting rate of Decomposition: Chemical composition - decomposition rate will be slow when detritus is rich in lignin and chitin and rate increases when detritus is rich in nitrogen and water soluble substances like sugars. • Climatic conditions — warm and moist environment favour decomposition and low temperature and anaerobiosis inhibit decomposition. ENERGY FLOW SUN- Main Source of energy of incident light is PHOTOSYNTHETICALLY ACTIVE RADIATION (PAR) 2- 10 % of PAR is captured by plants. Only a small fraction of this (stored as organic compounds) is transferred to consumers; the rest is used up in respiration and other life- supporting activities of the plants. As energy is transferred as food, most part is lost as heat at each stage (10% LAW) Sun Heat Producers inorganic Nutrient Pool Heat Consumers Decomposers Heat Unidirectional flow of Energy: Sun -> Producers -> Consumers Transfer of energy / food from the producer through a series of organisms is known as FOOD CHAINS. New Section I Page 5
  6. FOOD CHAINS Food chains represent energy flow through ecosystems. • Different steps in a food chain are TROPHIC LEVELS • Basic terms: Producers, Herbivores, Carnivores, Omnivores. I.GRAZING FOOD CHAIN (GFC) • Primary source of energy - Solar radiations. First trophic level includes - All Herbivores. -GFCs are Long-sized chains 2) DETRITUS FOOD CHAIN (DFC) Primary source of energy is Detritus. First trophic level includes Detritivores. Detritus Food Chains are small-sized chains. SAPROPHYTES: These include decomposers (fungi, bacteria) which feed on detritus. FOOD WEBS • The Natural Interconnection of Several Food Chains forms a FOOD WEB. Provides alternate pathways for food availability. Unlike food chains, food webs are never straight. Help in ecosystem development and stability. States that : during transfer of energy from one trophic level to another, only about 10% is stored at higher levels; remaining 90% is lost in respiration (heat) 4. ECOLOGICAL PYRAMIDS New Section I Page 6
  7. Developed by Charles Elton in 1927. • Pyramids are an expression of the relationship between organisms at different trophic levels in terms of their number, biomass or energy. • Three types of pyramids: Pyramid of Number 1. Pyramid of Biomass 2. Pyramid of energy 3. Pyramid of Number: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of number called pyramid of number. Pyramid of Biomass: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of biomass called pyramid of biomass. It can be of two types: a) Upright (in case of grassland ecosystem) b) Inverted (in case of pond ecosystem) Pyramid of energy: 3. The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of flow of energy called pyramid of energy. It is always upright. Limitations of Ecological Pyramids: • It does NOT consider the same species belonging to two or more trophic levels. • It is based on simple food chains, which hardly exist. It does NOT accommodate food webs. New Section I Page 7
  8. Saprophytes (decomposers) are NOT given any place in the ecosystem. Climax Community: Changes that lead finally to a community that is in near equilibrium with the environment. • It remains stable as long as the environment remains unchanged. The Rainforest is an example of climax community ecosystem. Ecological Succession: • Refers to predictable and orderly change in the composition or structure of a community. • May be initiated either by formation of new, unoccupied habitat or by some form of disturbance of an existing community. Sere — entire sequence of community that successively change in a given area. Seral stages — individual transitional communities. Seral Communities: Hydrosere - Community in freshwater Lithosere - Community on rock Pssamosere - Community on sand Halosere - Community in saline body Xerosere - Community in dry area Primary Succession If the development begins on an area that has not been previously occupied by a community. ' Pioneer species — lichens, phytoplankton, etc. Examples: - newly exposed rock or sand surface - a lava flow - glacial tills - newly formed lake, New Section I Page 8
  9. Secondary Succession If the community development is proceeding in an area from which a community was removed. • Pioneer species — grasses, wildflowers, algae. • Examples: an abandoned crop field cut-over forest natural forces such as wind storms and floods Succession in Plants: Hydarch succession • It takes place in wetter areas and the successional series progress from hydric to the mesic conditions. Phytoplankton in pond -> Submerged plant stage-> Submerged free floating plant stage -> Reed — swamp stage -> Marsh — meadow stage — scrub stage -> Forest Xerarch succession • It takes place in dry areas and the series progress from xeric to mesic condition. Bare rock -> Lichens and mosses -> Annual grasses -> Perennial grasses -> Shrubs -> Tall Trees The Nutrient Cycle • Also known as biogeochemical cycle. Environmental factors like soil, moisture, temperature, etc. regulate the rate of release of nutrients into the atmosphere. Standing state — amount of nutrients, such as C, N, P, Ca, etc. present in the soil at any given time. • Nutrients are never lost from the ecosystem; they are recycled time an New Section I Page 9
  10. again indefinitely. • There are two types: -Gaseous cycle - Sedimentary cycle CARBON CYCLE carbon constitutes 49 per cent of dry weight of organisms and is next only to water and 71 per cent carbon is found dissolved in oceans. This oceanic reservoir regulates the amount of carbon dioxide in the atmosphere . Fossil fuel also represent a reservoir of carbon. Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. According to one estimate 4x 1013 kg of carbon is fixed annually in the biosphere through photosynthesis. Carbon Cycle 1 Sunlight Photosynthesis Carbon dioxide (C02) Animal respiration Organic carbon Auto and factory emissions Plant respiration Root Å't respiration Decaying organisms Dead organisms and waste products Fossils and fossil fuels New Section I Page 10
  11. A considerable amount of carbon returns to the atmosphere as C02 through respiratory activities of the producers and consumers. Decomposers also contribute substantially to C02 pool by their processing of waste materials and dead organic matter of land or oceans. Some amount of the fixed carbon is lost to sediments and removed from circulation. Burning of wood, forest fire and combustion of organic matter, fossil fuel, volcanic activity are additional sources for releasing C02 in the atmosphere. Human activities have significantly influenced the carbon cycle. Rapid deforestation and massive burning of fossil fuel for energy and transport have significantly increased the rate of release of carbon dioxide into the atmosphere. - Sedimentary cycle Phosphorus is a major constituent of biological membranes, nucleic acids and cellular energy transfer systems. Many animals also need large quantities of this element to make shells, bones and teeth. The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates. When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants. New Section I Page I I
  12. Rock Phosphates Run-off to water bodies Soil Plants Phosphates Micro-organisms Dead plants and organisms Phosphorus Cycle Animals Living organisms Herbivores and other animals obtain this element from plants. The waste products and the dead organisms are decomposed by phosphate- solubilising bacteria releasing phosphorus. Unlike carbon cycle, there is no respiratory release of phosphorus into atmosphere. Ecosystem Services Humankind benefits from a multitude of resources and processes that are supplied by natural ecosystems. Collectively, these benefits are known as ecosystem services. Purify air and water 1. Decomposition of waste materials 2. 3. Cycle nutrients Pollinate crops 4. Maintain biodiversity 5. Robert Constanza and his colleagues have very recently tried to put price tags on nature's life-support services. Researchers have put an average price tag of US $33 trillion a year on these fundamental ecosystems services, which is largely taken for granted because they are free. New Section I Page 12

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