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Sep 12, 2020
Best Gk:

Ecosystem is a large community of living organisms like plants, animals and microbes in a particular area. 

Terrestrial and the aquatic

  • Examples of terrestrial ecosystems are grassland,Forest, and desert.
  • Examples of aquatic ecosystems are lake,wetland,pond, river.
  • Crop fields and an aquarium may also be considered as man-made ecosystems.
  • Vertical distribution of different species occupying different levels is called stratification.

Ecosystem of different components are:

(i) Productivity; 

(ii) Decomposition; 

(iii) Energy flow; and 

(iv) Nutrient cycling.  

∙ The consumers are represented by the zooplankton, the free swimming and bottom  dwelling forms. 

∙ The decomposers are the fungi, bacteria and flagellates especially abundant in the  bottom of the pond. 

∙ This type of system performs all functions of any ecosystem and of the biosphere as a  whole, i.e., conversion of inorganic into organic material with the help of the  radiant energy of the sun.

Primary type production:

It is called as the amount of organic matter  produced per unit area over a time period by plants during photosynthesis. ∙

∙ It can be divided into gross primary productivity (GPP) and net primary  productivity (NPP). 

∙ Gross primary productivity of an ecosystem is the rate of production of organic  matter during photosynthesis. 

∙ A considerable amount of GPP is utilised by plants in respiration. ∙ Gross primary productivity minus respiration losses (R), is the net primary  productivity (NPP). 

∙ Net primary productivity is the available biomass for the consumption to  heterotrophs (herbiviores and decomposers). 

∙ Secondary productivity is defined as the rate of formation of new organic matter  by consumers. 

∙ Primary productivity depends on the plant species inhabiting a particular area. ∙ It also depends on a variety of environmental factors, availability of nutrients and  photosynthetic capacity of plants.  

∙ Of this, despite occupying about 70 per cent of the surface, the productivity of the  oceans are only 55 billion tons. 

∙ The important steps in the process of decomposition are fragmentation, leaching,  catabolism, humification and mineralisation. 

∙ Detritivores (e.g., earthworm) break down detritus into smaller particles. This  process is called fragmentation. 

∙ The process of leaching, water soluble inorganic nutrients go down into the soil  horizon and get precipitated as unavailable salts. 

The catabolism is called Bacterial and fungal enzymes degrade detritus into simpler inorganic substances.  

∙ Being colloidal in nature it serves as a reservoir of nutrients. 

∙ Decomposition is largely an oxygen-requiring process. 

∙ Moist and Warm environment favour decomposition whereas low temperature and  anaerobiosis inhibit decomposition resulting in build up of organic materials. ∙ The detritus food chain (DFC) begins with dead organic matter.

∙ It is made up of decomposers which are heterotrophic organisms, mainly fungi and  bacteria. 

∙ They meet their energy and nutrient requirements by degrading dead organic  matter or detritus. 

∙ These are also known as Saprotrophs (sapro:to decompose). 

∙ As against this, in a terrestrial ecosystem, a much larger fraction of energy flows  through the detritus food chain than through the GRAZING FOOD CHAIN. ∙ Detritus food chain may be connected with the grazing food chain at some levels:  some of the organisms of DFC are prey to the GFC animals, and in a natural  ecosystem, some animals like cockroaches, crows, etc., are omnivores. ∙ These natural interconnection of food chains make it a food web. ∙ The consumers that feed on these herbivores are carnivores, or more correctly  primary carnivores (though secondary consumers). 

∙ Those animals that depend on the primary carnivores for food are labeled  secondary carnivores. 

∙ Organisms occupy a place in the natural surroundings or in a community  according to their feeding relationship with other organisms. 

∙ Based on the source of their nutrition or food, organisms occupy a specific place  in the food chain that is known as their trophic level.  

∙ When any organism dies it is converted to detritus or dead biomass that serves as  an energy source for decomposers. 

∙ Organisms at each trophic level depend on those at the lower trophic level for their  energy demands. 

∙ Each trophic level has a certain mass of living material at a particular time called  as the standing crop. 

∙ The standing crop is measured as the mass of living organisms (biomass) or the  number in a unit area. 

∙ The biomass of a species is expressed in terms of fresh or dry weight.

∙ Biomass measurement of dry weight is more accurate.

∙ Each bar in the energy pyramid indicates the amount of energy present at each  trophic level in a given time or annually per unit area. 

∙ These changes lead finally to a community that is in near equilibrium with the  environment and that is called a climax community. 

∙ The individual transitional communities are termed seral stages or seral  communities. 

∙ Succession is hence a process that starts where no living organisms are there – these could be areas where no living organisms ever existed, say bare rock; or in  areas that somehow, lost all the living organisms that existed there. 

∙ The former is called primary succession, while the latter is termed secondary  succession. 

∙ Examples of areas where primary succession occurs are newly cooled lava, bare  rock, newly created pond or reservoir. 

∙ The establishment of a new biotic community is generally slow. ∙ Before a biotic community of diverse organisms can become established, there  must be soil. 

∙ Depending mostly on the climate, it takes natural processes several hundred to  several thousand years to produce fertile soil on bare rock.  

∙ Since some soil or sediment is present, succession is faster than primary  succession. 

∙ Based on the nature of the habitat – whether it is water (or very wet areas) or it is  on very dry areas – succession of plants is called hydrach or xerarch, respectively.

∙ Hydrarch succession takes place in wetter areas and the successional series  progress from hydric to the mesic conditions. 

∙ As against this, xerarch successiontakes place in dry areas and the series progress  from xeric to mesic conditions.

∙ In primary succession on rocks these are usually lichens which are able to secrete  acids to dissolve rock, helping in weathering and soil formation. 

∙ These later pave way to some very small plants like bryophytes, which are able to  take hold in the small amount of soil. 

∙ They are, with time, succeeded by bigger plants, and after several more stages,  ultimately a stable climax forest community is formed. 

∙ The climax community remains stable as long as the environment remains  unchanged. 

∙ With time the xerophytic habitat gets converted into a mesophytic one. succession,  particularly primary succession, is a very slow process, taking maybe thousands of  years for the climax to be reached. 

∙ Another important fact is to understand that all succession whether taking place in  water or on land, proceeds to a similar climax community – the mesic. ∙ The movement of nutrient elements through the various components of an  ecosystem is called nutrient cycling. 

∙ Another name of nutrient cycling is biogeochemical cycles (bio: living organism,  geo: rocks, air, water). 

∙ Nutrient cycles are of two types: (a) gaseous and (b) sedimentary. 

Phosphorus Cycle

Phosphorus is a important 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. 

∙ Herbivores and other animals obtain this element from plants. 

∙ The waste products and the dead organisms are decomposed by phosphate solubilizing bacteria releasing phosphorus. 

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