Explore topic-wise InterviewSolutions in .

E.J. Kormondy .

There is an interaction between all organism and their physical environment that maintain a balance between the organisms & physical environment. exchange of the substance and flow of energy. It is called as Ecosystem or Ecological system.

Ecosystem is a functional unit of ecology.Term ecosystem was first used by British ecologist Arthur Tansley. Tensley defined ecosystem as the interaction between the biotic factors (plants, animals & other organisms) and abiotic factor (weather, soil.air & temperature).

Before Tansley, Karl Mobius (1877) called it as Biocoenosis, Forbes(1987) as Microcosm and Mishra as Ecocosm. But the ecosystem, is universally accepted.

Symbiotic bacteria — Azobactor & Rhizobium.
Blue green algae — Nostoc & Anabaena

Producers (Plants) are called as primary producers and the Quaternary producers are called as secondary producers.

Artificial ecosystem

The amount of abiotic substance (inorganic nutrients) in an ecosystem at a specific time is called as standing state. It tends to very form season to season and ecosystem to ecosystem.
The total amount or number of living thing (biotic) in a particular area at any given time is called as standing crop.

In an ecosystem, standing crop is the mass of living material in each trophic level at a particular time. Whereas standing state refers to the amount of nutrients in the soil at any given time.

The pioneer species invade a bare area and pave way for other species.

Dead plant and animal remains and their faecal matter. They obtain energy by decomposing the dead materials.

Primary succession occurs on newly cooled lava or bare rocks or newly created pond or reservoir.

i. Primary succession in water 

• The pioneer species are phytoplanktons. 

• The phytoplanktons are replaced by free-floating angiosperms.

• Then, rooted angiosperms invade sedges, grasses and finally the trees. 

• At last, a stable climax forest is formed. 

• An aquatic habitat is converted into mesic habitat. 

ii. Primary succession on rocks 

• Lichens are the pioneer species on a bare area. 

• The lichen secretes some acids to dissolve rock and help in weathering and soil formation. 

• Later, some small bryophytes invade and hold the small amount of soil.

• The bryophytes are succeeded by herbs, shrubs and ultimately big trees. 

• At last, a stable climax forest is formed. 

• The xerophytic habitat gets converted into a mesophytic one.

It is true that any change in the abiotic/biotic factor will arrest a particular seral stage leading to a pre-climax condition before the climax stage is achieved. This can happen in cases of forest fires, landslide, change in soil characteristics, increase in herbivore population leading to overgrazing.

Biotic (living) components includes all living organisms like plants, animals, fungi and bacteria. They form the trophic structures of any ecosystem.

There are three zones, littoral, limnetic and profundal. The littoral zone, which is closest to the shore with shallow water region, allows easy penetration of light. It is warm and occupied by rooted plant species. The limnetic zone refers the open water of the pond with an effective penetration of light and domination of planktons.

The deeper region of a pond below the limnetic zone is called profundal zone with no effective light penetration and predominance of heterotrophs. The bottom zone of a pond is termed benthic and is occupied by a community of organisms called benthos (usually decomposers).

A pond ecosystem consists of dissolved inorganic (CO₂ , O₂ , Ca, N and Phosphate) and organic substances (amino acids and humic acid) formed from the dead organic matter. The function of pond ecosystem is regulated by few factors like the amount of light, temperature, pH value of water and other climatic conditions.

Biotic components: They constitute the producers, variety of consumers and decomposers (microorganisms).

(a) Producers: A variety of phytoplanktons like Oscillatoria, Anabaena, Eudorina, Volvox and Diatoms. Filamentous algae such as Ulothrix, Spirogyra, Cladophora and Oedogonium; floating plants Azolla, Salvia, Pistia, Wolffia and Eichhornia; sub-merged plants Potamogeton and Phragmitis; rooted floating plants Nymphaea and Nelumbo; macrophytes like Typha and Ipomoea, constitute the major producers of a pond ecosystem.

(b) Consumers: The animals represent the consumers of a pond ecosystem include zooplanktons like Paramoecium and Daphnia (primary consumers); benthos (bottom living animals) like molluscs and annelids; secondary consumers like water beetles and frogs; and tertiary consumers (carnivores) like duck, crane and some top carnivores which include large fish, hawk and man, etc.

(c) Decomposers: They are also called as microconsumers. They help to recycle the nutrients in the ecosystem. These are present in mud water and bottom of the ponds. Example: Bacteria and Fungi. Decomposers perform the process of decomposition in order to enrich the nutrients in the pond ecosystem.

(c) Benthic zone

(d) Littoral, limnetic, profundal and benthic

Correct Answer is: (d) a and b