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:
(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 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.