Organisms interact with each other and also with physical conditions that are present in their habitats. The organisms and the physical features of the habitat form an ecological complex i.e. Ecosystem. The term ecosystem was coined by A.G. Tansley in 1935. The function of ecosystem is related to the flow of energy and cycling of materials through structural components of the ecosystem. All ecosystems of the earth are connected to one another, e.g., river ecosystem is connected with ecosystem of oceans.

Components of Ecosystem

Ecosystem has biotic and abiotic component.

Abiotic Components: Abiotic components are basic inorganic and organic compounds such as soil, water, calcium, oxygen, carbonates, and phosphates. It also includes climatic components such as moisture, wind currents and solar radiation etc.

Biotic Components: It includes living elements of the ecosystem and includes producers, consumers decomposers and transformers.

(a)  Producers: The producers are autotrophic like chemosynthetic and photosynthetic bacteria, blue green algae and all other green plants. They use radiant energy of sun in photosynthetic process in which CO2 is assimilated and the light energy is converted into chemical energy and O2 is evolved as a by-product.

(b)  Consumers: They are heterotrophic living members of ecosystem, which consume the food synthesized by producers. They are of three types.

(i)   Primary consumers: Those are purely herbivorous animals that are dependent for their food and producers or green plants. The herbivores of ecosystem are known as “key industry animals”.

(ii)  Secondary consumers: These are carnivores and omnivores, which eat primary consumers and producers.

(iii) Tertiary consumers: These top carnivores, which feed upon other carnivores, omnivores and herbivores.

(c)  Decomposers and transformers: They are living components of the ecosystem and are fungi and bacteria. Decomposers attack the dead remains of producers and consumers and degrade the complex organic substances into simpler compounds. These simple organic matters are attacked by another kind of bacteria, transformers which finally change these organic compounds into the inorganic form that are suitable for reuse by producers or green plants.

 (d) Detritivore: These are those organisms which eats detritus, which consist of organic litter, debris and dung. Examples of detritivore are flies, cockroach, crabs, earthworms, wood beetles and carpenter ants.

Food Chain

Organisms of an ecosystem are linked together in food chains. Green plants alone are able to trap in solar energy and convert it into chemical energy. The plants are eaten by consumers, which are being eaten by their predators. Thus, food from one trophic level reaches the other trophic level and in this way a chain is established. This is known as food chain. A food chain many be defined as the transfer of energy and nutrients through succession of organisms through repeated process of eating and being eaten.

Food Web

In ecosystem, one organism does not depend wholly on another. The resources are shared specially at the beginning of the chain. The marsh plants are eaten by variety of insects, birds, mammals and fishes and some of the animals are eaten by several predators. Similarly, in the food chain, grass-mouse-snakes-owls, sometimes mice are not eaten by snakes but directly by owls. This type of inter relationship inter links the individuals of the whole community. In this way, food chains become interlinked. A complex of interrelated food chains makes up food web.

Phenomenon in Food chain or Web

Biomagnification, also known as bioamplification or biological magnification, occurs when the concentration of a substance, such as DDT or mercury, in an organism exceeds the background concentration of the substance in its diet.[1] This increase can occur as a result of: Persistence – where the substance can't be broken down by environmental processes

Food chain energetic – where the substance concentration increases progressively as it moves up a food chain

Low or non-existent rate of internal degradation or excretion of the substance – often due to water-insolubility

Bioaccumulation occurs within a trophic level, and is the increase in concentration of a substance in certain tissues of organisms' bodies due to absorption from food and the environment.

Bio concentration is defined as occurring when uptake from the water is greater than excretion.Thus, bioconcentration and bioaccumulation occur within an organism, and biomagnification occurs across trophic (food chain) levels.

Biodilution is also a process that occurs to all trophic levels in an aquatic environment; it is the opposite of biomagnification, thus a pollutant gets smaller in concentration as it progresses up a food web.

Ecological Pyramid

At each step in the food chain a considerable portion of the potential energy is lost as heat. As a result, organisms in each trophic level pass on lesser energy to the next trophic level than they actually received. Longer the food chain the lesser energy is available for final members. Because of this tapering off of available energy in the food chain, a pyramid is formed that is known as ecological pyramid. The ecological pyramids are of three types:

(i)   Pyramid of number shows the number of organisms of each trophic level. In grassland and pond ecosystem pyramid is upright while in forest ecosystem it may be of different shapes. For example it can be inverted in a case where a single tree can support number of birds and microorganism.

(ii)  Pyramid of biomass: shows the total dry weight and other suitable measures of total amount of living matter. The biomass is least of producers and upright in case of grassland and forest ecosystem.

(iii) Pyramid of energy: Show the rate of energy flow and or productivity at successive trophic levels. The pyramid of energy is always upright.