ECOSYSTEMS CHAPTER 13 CLASS XII BIOLOGY ECOSYSTEMS The interactin between the living rganism and the nn-living envirnment is called ecsystem. ECOSYSTEM STUCTURE AND FUNCTION: Interactin f bitic and abitic cmpnents results in a physical structure that is characteristic f each type f ecsystem. Identificatin and descriptin f plant and animal species f an ecsystem gives its species cmpsitin. Vertical distributin f different species ccupying different levels is called stratificatin. The cmpnents f the ecsystem are seen t functin as a unit: Prductivity. Decmpsitin. Energy flw and Nutrient cycle. Descriptin f pnd as an ecsystem: The abitic cmpnents include all disslved inrganic and rganic substances and the rich sil depsit at the bttm f the pnd. The slar input, cycle f temperature, day length, regulates the rater f functin f the entire pnd. The prducer (auttrphic) includes phytplanktn, sme algae and the flating, submerged and marginal plants fund in edge f pnd. The cnsumers are represented by zplanktn, free swimming and bttm dwelling animals. The decmpsers are the fungi, bacteria especially abundant at the bttm f the pnd. Basic events (in terms f functin) in an ecsystem: Cnversin f inrganic int rganic material (phtsynthesis) by prducers. Cnsumptin f the auttrphs by hetertrphs. Decmpsitin and mineralizatin f the dead rganic matter t release them back fr reuse by the auttrphs There is unidirectinal flw f energy twards the higher trphic levels and its dissipatin and lss as heat t the envirnment. PRODUCTIVITY: Primary prductivity: The amunt f bimass r rganic matter prduced per unit area ver a time perid by plants during phtsynthesis. It is expressed in terms f weight (g-2) r energy (kcal m-2) The rate f bimass prductin is called prductivity.
Grss primary prductivity: (GPP) is the rate f prductin f rganic matter during phtsynthesis. Net primary prductivity: A cnsiderable amunt f energy is utilized by plants in respiratin. Grss primary prductivity minus respiratin lsses (R) is the net primary prductivity. GPP R = NPP. Net primary prductivity is the available bimass fr the cnsumptin t hetertrphs (herbivre and decmpsers. Secndary prductivity: is defined as the rate f frmatin f new rganic matter by the cnsumer. DECOMPOSITION: Earthwrm is said t be friends f farmer: Breakdwn the cmplex rganic matter. Lsening f the sil helps in aeratin and entry f rt. The decmpsers break dwn cmplex rganic matter int inrganic substances like carbn dixide, water and nutrients, called decmpsitin. Dead plant remains such as leaves, bark, flwers and dead remains f animals, including fecal matter, cnstitute the detritus. The prcess f decmpsitin cmpleted in fllwing steps: Fragmentatin : Break dwn f detritus int smaller particles by detritivre (earthwrm). Leaching: Water sluble inrganic nutrients g dwn int the sil hrizn and get precipitated as unavailable salts. Catablism : Bacterial and fungal enzymes degrade detritus int simple inrganic substances. Humificatin: Accumulatin f dark clured amrphus substances called humus. Imprtance f humus: Highly resistance t micrbial actin. Underg decmpsitin at an extremely slw rate. Being cllidal in nature, it serves as reservir fr nutrients. Mineralizatin: The humus is further degraded by sme micrbes and release f inrganic nutrients ccur. Factr affects rate f decmpsitin: Decmpsitin is largely an xygen-requiring prcess. Detritus rich in chitin and lignin has slw rate f decmpsitin. Detritus rich in nitrgen and water-sluble substance like sugar has faster decmpsitin. Temperature and sil misture are mst imprtant climatic factr that regulate decmpsitin Warm and mist envirnment favr decmpsitin. Lw temperature, dryness and anerbisis inhibit decmpsitin.
ENERGY FLOW IN ECOSYSTEM: Except fr deep sea hydrthermal ecsystem, sun is the nly surce f energy fr all ecsystems n earth. Less than 50% f incident slar radiatin isphtsynthetically active radiatins. (PAR). Plants capture 2-10 % f PAR and used in phtsynthesis. All rganisms depend n the prducers, either directly r indirectly. Energy flw in the ecsystem is unidirectinal i.e. energy transferred frm prducer t cnsumers. Energy transfer is nt abslute, and spntaneus, unless energy is degraded it can nt be transfer. When energy transferred frm ne trphic level t anther, lt f energy lst in the frm f heat t the envirnment. Only 10% f energy transferred frm ne trphic level t ther. Fd chain: Grazing fd chain: it extends frm prducers thrugh herbivre t carnivre.
Detritus fd chain: Begins with dead rganic matter (detritus) and pass thrugh detritus feeding rganism in sil t rganisms feeding n detritus-feeders. In aquatic ecsystem GFC is the majr cnduit fr energy flw. In terrestrial ecsystems a much larger fractin f energy flws thrugh the detritus fd chain than thrugh GFC Different fd chains are naturally intercnnected e.g. a specific herbivre f ne fd chain may serve as fd f carnivres f ther fd chains. Such intercnnected matrix f fd chains is called fd web. Trphic level: A grup f rganism irrespective f their size having same surce f energy r similar fd habit cnstitute a trphic level. Standing crp: each trphic level has a certain mass f living material at a particular time called as the standing crp. The standing crp is measured as the mass f living rganisms (bimass) r the number in a unit area. The number f trphic levels in a fd chain is restricted by 10 % flw f energy, less amunt f energy available t the last trphic level. ECOLOGICAL PYRAMID: The base f the pyramid is brad and it narrws dwn at the apex. The similar shape is btained when fd r energy relatinship between rganisms at different trphic level. The relatinship can be expressed in terms f number, energy r bimass.
The base f the pyramid represented by prducer and apex is the tp cnsumer; ther trphic levels are in between. In mst ecsystems, all the pyramids, f number, f energy and bimass are upright. The pyramid f number in a tree ecsystem is inverted. The pyramid f bimass in sea als inverted because the bimass f fishes is far exceeds that f phytplanktn. Pyramid f energy is always upright, can never be inverted, because when energy flws frm a particular trphic level t the next, sme energy is always lst as heat at each step. Limitatins f eclgical pyramids: It des nt take int accunt the same species belnging t tw r mre trphic levels. It assumes a simple fd chain, it never exits in nature. It dse nt accmmdate fd web. Saprphytes are nt given place in eclgical pyramids. ECOLOGICAL SUCCESSION: The gradual and fairly predictable change in the species cmpsitin f a given area is called eclgical successin. Cmpsitin and structure f the cmmunity cnstantly change in respnse t changing envirnmental cnditin. This change is rderly and sequential, parallel with the changes in the physical envirnment.
All the changes lead finally t a cmmunity that is in near equilibrium with the envirnment and that is called climax cmmunity. During successin sme species clnize and area and their ppulatins becme mre numerus, whereas ppulatins f ther species decline and even disappear. The entire sequences f cmmunities that successively change in a given area are called sere. The individual transitinal cmmunities are termed as seral stages. In the successive seral stages there is a change in the diversity f species f rganisms, in crease in number f species and ttal bimass. Primary successin: successin that starts where n living rganisms are there- these culd be areas where n living rganism ever existed may be a bare rck r new water bdy. Secndary successin: successin that starts in areas that smehw, lst all the living rganisms that existed there. Primary successin ccurs in:- newly cled lava, bare rck, Newly created pnd r reservir. Secndary successin begins in areas where natural bitic cmmunities have been destryed such as In abandned farm lands. Burned r cut frest, land that have been flded Since sme sil r sediment is present, secndary successin is faster than primary successin. Successin in plants: Based n the nature f habitat whether it is water r it is n very dry areas- successin f plants is calledhydrarch r xerarch. Hydrarch successin takes place in water areas and the successinal series prgress frm hydric t mesiccnditin. Xerarch successin takes place in dry areas and the series prgress frm xeric t mesic cnditins. Bth hydrarch and xerarch successins lead t medium water cnditins (mesic) neither t dry (xeric) nr t wet (hydric) Xerarch successin: Successin in bare rck: The species that invades bare area are called pineer species. In primary successin n bare rck the pineer species is the lichen. Lichen secretes acid t disslve rck, helping in weathering and sil frmatin. The little sil, leads t grwth f bryphytes (msses). The msses speed up the prcess f sil accumulatin by trapping wind-blwn particles. Lichen mss carpet prvides suitable substratum fr the germinatin f seeds f herbaceus plants. Gradually mre sil is accumulated and herbaceus species make way fr the invasin f shrubs fllwed bytrees. The climax cmmunity is generally dminated by trees. Hydrarch (successin in aquatic envirnment) In primary successin in water, the pineer species arephytplanktn.
Zplanktns. Sub merged plant stage. (rted hydrphytes) Sub merged and free-flating plant stage. Reed-swamp stage. Marsh-meadw stage. Shrub stage Trees The climax again wuld be the frest All the successin whether taking place in water r n land, prceeds t a similar climax cmmunity the mesic. NUTRIENT CYCLING: Organism needs cnstant supply f nutrients t grw, reprduce, and regulate varius bdy functins. Standing state: the amunt nutrients such as carbn, nitrgen, phsphrus, calcium etc. present in sil at any given time. Nutrient cycling: The mvement f nutrient elements thrugh the varius cmpnent f an ecsystem is called nutrient cycling. Anther name f nutrient cycling is bigechemical cycle. Nutrient cycles are f tw types: Gaseus cycle Sedimentary cycle. The reservir fr gaseus type f nutrient cycle (nitrgen, carbn) exists in the atmsphere. The reservir fr sedimentary cycle (sulphur, phsphrus) is Earth s crust. Envirnmental factrs like sil, misture, ph temperature regulate the rate f release f nutrient int the atmsphere. The functin f the reservir is t meet the deficit which ccurs due t imbalance in the rate f influx and efflux. Ecsystem Carbn cycle: Carbn cnstitutes 49 percent f dry weight f rganism. Out f ttal glbal carbn: 71 percent carbn fund disslved in cean. Abut 1 percent in the atmsphere. 4 X 10 13 kg f carbn is fixed in the bisphere by phtsynthesis, annually. Large amunt f carbn returned t the atmsphere as CO2 thrugh respiratin f prducers and cnsumers. Decmpsers als return CO2 t reservir during decmpsitin prcess. Sme amunt f Carbn is lst t sediments and remved frm circulatin. Burning wd, frest fire, cmbustin f rganic matter, fssil fuel, vlcanic activities are additinal surces fr releasing CO2 t atmsphere. Influence f human activity n Carbn cycling.
Rapid defrestatin. Massive burning f fssil fuel fr energy and transprt Increased the rate f release f CO2 int the atmsphere. Ecsystem Phsphrus cycle: Phsphrus is a majr cnstituent f bilgical membranes, nucleic acids and cellular energy transfer system(atp) Animals need phsphrus t make shell, bnes and teeth. Reservir pl f phsphrus is the rck, which cntain phsphrus in the frm f phsphates. During weathering f rck small amunt f phsphates disslved in sil slutin and are absrbed by the rts f the plants. Herbivre and ther animals btain rganic frm f phsphrus frm plants.
The waste prduct and dead rganisms are decmpsed by phsphate-slubilising bacteria releasing phsphrus. Hw phsphrus cycle differs frm carbn cycle? There is n respiratry release f phsphrus int atmsphere. Atmspheric inputs f phsphrus thrugh rainfall are much smaller. Gaseus exchange f phsphrus between rganism and envirnment are negligible. ECOSYSTEM SERVICES: The prducts f ecsystem prcesses are named as ecsystem services. Healthy frest ecsystems purify air and water. Mitigate drughts and fld. Cycle nutrients. Generates fertile sil. Prvide wildlife habitat. Maintain bidiversity. Pllinate crps. Prvide strage site fr carbn Prvides aesthetic, cultural and spiritual values PAR: GAP: NPP: DFC: GFC: Phtsynthetically Active Radiatin Grss Primary Prductivity Net Primary Prductivity Detritus Fd Chain Grazing Fd chain **************************************