Ecosystem

1 An Ecosystem can be visualised as a functional unit ofnature, where living organisms interact among themselvesand also with the surrounding physical varies greatly in size from a small pond to alarge forest or a sea. Many ecologists regard the entirebiosphere as a global Ecosystem , as a composite of alllocal ecosystems on Earth. Since this system is too muchbig and complex to be studied at one time, it is convenientto divide it into two basic categories, namely theterrestrial and the aquatic . Forest, grassland and desertare some examples of terrestrial ecosystems ; pond, lake,wetland, river and estuary are some examples of aquaticecosystems. Crop fields and an aquarium may also beconsidered as man-made will first look at the structure of the Ecosystem , inorder to appreciate the input (productivity), transfer ofenergy (food chain/web, nutrient cycling) and the output(degradation and energy loss).

2 We will also look at therelationships cycles, chains, webs that are created asa result of these energy flows within the system and theirinter- Structureand Ecosystem STRUCTURE AND FUNCTIONIn chapter 13, you have looked at the various components of theenvironment- abiotic and biotic. You studied how the individual bioticand abiotic factors affected each other and their surrounding. Let us lookat these components in a more integrated manner and see how the flow ofenergy takes place within these components of the of biotic and abiotic components result in a physicalstructure that is characteristic for each type of Ecosystem . Identificationand enumeration of plant and animal species of an Ecosystem gives itsspecies composition.

3 Vertical distribution of different species occupyingdifferent levels is called stratification. For example, trees occupy topvertical strata or layer of a forest, shrubs the second and herbs and grassesoccupy the bottom components of the Ecosystem are seen to function as a unit whenyou consider the following aspects:(i)Productivity;(ii)Decompositio n;(iii)Energy flow; and(iv)Nutrient understand the ethos of an aquatic Ecosystem let us take a smallpond as an example. This is fairly a self-sustainable unit and rather simpleexample that explain even the complex interactions that exist in an aquaticecosystem. A pond is a shallow water body in which all the abovementioned four basic components of an Ecosystem are well abiotic component is the water with all the dissolved inorganic andorganic substances and the rich soil deposit at the bottom of the solar input, the cycle of temperature, day-length and other climaticconditions regulate the rate of function of the entire pond.

4 The autotrophiccomponents include the phytoplankton, some algae and the floating,submerged and marginal plants found at the edges. The consumers arerepresented by the zooplankton, the free swimming and bottom dwellingforms. The decomposers are the fungi, bacteria and flagellates especiallyabundant in the bottom of the pond. This system performs all the functionsof any Ecosystem and of the biosphere as a whole, , conversion ofinorganic into organic material with the help of the radiant energy of thesun by the autotrophs; consumption of the autotrophs by heterotrophs;decomposition and mineralisation of the dead matter to release them backfor reuse by the autotrophs, these event are repeated over and over is unidirectional movement of energy towards the higher trophiclevels and its dissipation and loss as heat to the PRODUCTIVITYA constant input of solar energy is the basic requirement for any ecosystemto function and sustain.

5 Primary production is defined as the amount of2022-23243 Ecosystem biomass or organic matter produced per unit area over a time period byplants during photosynthesis. It is expressed in terms of weight (gm 2) orenergy (kcal m 2). The rate of biomass production is called is expressed in terms of gm 2 yr 1 or (kcal m 2) yr 1 to compare theproductivity of different ecosystems . It can be divided into gross primaryproductivity (GPP) and net primary productivity (NPP). Gross primaryproductivity of an Ecosystem is the rate of production of organic matterduring photosynthesis. A considerable amount of GPP is utilised by plantsin respiration. Gross primary productivity minus respiration losses (R),is the net primary productivity (NPP).

6 GPP R = NPPNet primary productivity is the available biomass for the consumptionto heterotrophs (herbiviores and decomposers). Secondary productivityis defined as the rate of formation of new organic matter productivity depends on the plant species inhabiting aparticular area. It also depends on a variety of environmental factors,availability of nutrients and photosynthetic capacity of plants . Therefore,it varies in different types of ecosystems . The annual net primaryproductivity of the whole biosphere is approximately 170 billion tons(dry weight) of organic matter. Of this, despite occupying about 70 percent of the surface, the productivity of the oceans are only 55 billion of course, is on land.

7 Discuss the main reason for the lowproductivity of ocean with your DECOMPOSITIONYou may have heard of the earthworm being referred to as the farmer s friend . This is so because they help in the breakdown of complex organicmatter as well as in loosening of the soil. Similarly, decomposers breakdown complex organic matter into inorganic substances like carbondioxide, water and nutrients and the process is called plant remains such as leaves, bark, flowers and dead remains ofanimals, including fecal matter, constitute detritus, which is the rawmaterial for decomposition. The important steps in the process ofdecomposition are fragmentation, leaching, catabolism, humification ( , earthworm) break down detritus into smaller process is called fragmentation.

8 By the process of leaching, water-soluble inorganic nutrients go down into the soil horizon and get precipitatedas unavailable salts. Bacterial and fungal enzymes degrade detritus intosimpler inorganic substances. This process is called as is important to note that all the above steps in decomposition operatesimultaneously on the detritus (Figure ). Humification andmineralisation occur during decomposition in the soil. Humification leads2022-23244 BIOLOGYto accumulation of a dark coloured amorphous substance called humusthat is highly resistant to microbial action and undergoes decompositionat an extremely slow rate. Being colloidal in nature it serves as a reservoirof nutrients. The humus is further degraded by some microbes and releaseof inorganic nutrients occur by the process known as is largely an oxygen-requiring process.

9 The rate ofdecomposition is controlled by chemical composition of detritus andclimatic factors. In a particular climatic condition, decomposition rateis slower if detritus is rich in lignin and chitin, and quicker, if detritus isrich in nitrogen and water-soluble substances like sugars. Temperatureand soil moisture are the most important climatic factors that regulatedecomposition through their effects on the activities of soil and moist environment favour decomposition whereas lowtemperature and anaerobiosis inhibit decomposition resulting in buildup of organic Diagrammatic representation of decomposition cycle in a terrestrial ENERGY FLOWE xcept for the deep sea hydro-thermal Ecosystem , sun is the only sourceof energy for all ecosystems on Earth.

10 Of the incident solar radiation lessthan 50 per cent of it is photosynthetically active radiation (PAR). Weknow that plants and photosynthetic bacteria (autotrophs), fix Sun sradiant energy to make food from simple inorganic materials. Plantscapture only 2-10 per cent of the PAR and this small amount of energysustains the entire living world. So, it is very important to know how thesolar energy captured by plants flows through different organisms of anecosystem. All organisms are dependent for their food on producers, eitherdirectly or indirectly. So you find unidirectional flow of energy from thesun to producers and then to consumers. Is this in keeping with the firstlaw of thermodynamics?