Ecosystem
(1) The term ecosystem was coined by A.G. Tansley in 1935.
(2) Structure: The structure of any ecosystem is composed of two components:
(i) Abiotic factors. (ii) Biotic factors
(3) Abiotic factors: The abiotic factors of an ecosystem include the non-living substances
Of the environment. eg. water, soil, air, light, temperature, minerals, climate, pressure etc. The biotic factors of the ecosystem depend on the abiotic factors for their survival.
(4) Biotic factors: The biotic factor includes the living organisms of the environment. e.g.
Plants, animals, bacteria, viruses etc. The biotic factors of an ecosystem are classified into
three main groups, namely:
(i) Producers
(ii) Consumers
(iii) Reducers or Decomposers.
(i) Producer
(a) The organisms which carry out photosynthesis constitute the producers of an ecosystem. eg. Plants algae and bacteria.
(b) The producers depend on the abiotic factors of the ecosystem for producing energy. They are provided with chlorophyll.
(c) Chlorophyll is used in the synthesis of energy rich compounds with the utilization of abiotic factors like light, CO, water and Producers: minerals.
(d) A portion of the energy synthesized, is used by the producers for their growth and survival and the remaining energy is stored for future use.
(ii) Consumers:
(a)Consumers are organisms which eat or devour other organisms.
(b) The consumers can be categorized into three or more types.
(c) Primary consumers, secondary consumers, and tertiary consumers.
(iii) Reducers or Decomposers:
(a) Decomposers are heterotrophic organisms that break down dead organisms and their waste products.
(b) These organisms, which include fungi and bacteria, secrete enzymes that digest dead organisms and debris into smaller bits.
(c) These organisms also produce oxygen, which allows them to decompose .These molecules are absorbed by the reducers.
(d)The reducers release molecules to the environment after taking energy as chemicals, which the producers then use again.
Energy flow:
(1) The Grabbing of energy from one trophic level to another trophic level is called energy flow. (2) The flow of energy in an ecosystem is bidirectional. That is, it flows from the producer level to the consumer level and never in the reverse direction. Hence energy can be used only once in the ecosystem.
(3) But the minerals circulate and recirculate many times in the ecosystem.
(4) A large amount of energy is lost at each trophic level.
(5) It is estimated that 90% of the energy is lost when it is transferred from one trophic level to another..
(6) Only about 10% of the biomass is transferred from one trophic level to the next one is a food chain. And only about 10% of chemical energy is retained at each trophic level. This is called the 10% law of Lindeman (1942).
Ecological pyramids:
(1) The number, biomass and energy of organisms gradually decrease from the producer level to the consumer level. This can be represented in the form of a pyramid called ecological pyramid.
(2) Ecological pyramid is the graphic representation of the number, biomass, and energy of
(3) The use of the ecological pyramid was first described by Charles Elton in 1927.the successive trophic levels of an ecosystem.
(4) In the ecological pyramid, the producer forms the base and the final consumer occupies
(5) There are three types of ecological pyramids, namely:the apex.
(a) The pyramid of number:
Generally, the number of individuals at the trophic level decreases from the producer level to the consumer level, meaning in an ecosystem the number of producers is much higher. The number of herbivores is far less than the number of producers.Similarly, the number of carnivores is lesser than the
Herbivores.
(i) In a cropland ecosystem: In croplands the crops are more in numbers. The grasshoppers feeding on crop plants are lesser in number. The frogs feeding on grasshoppers are still lesser in number.
The snakes feeding on frogs are fewer in number.
Crop -> Grasshopper -> Frogs > Snakes →→ Hawks
(ii) In a grassland ecosystem: In grassland the grasses are there in large numbers.
The consumers decrease in the following order.
Grass> Grasshopper > Lizard Hawk Grass → Rabbit → Fox -> Lion
(iii) In a pond ecosystem: The number in a pond ecosystem decreases in the following order.
Phytoplankton-> Zooplankton-> Fishes > Snakes
(b) The pyramid of biomass:
Biomass refers to the total weight of living matter per unit area. In an ecosystem the biomass decreases from the producer level to the consumer level.
(c) Pyramid of energy:
The energy flows in an ecosystem from the producer level to the consumer level. At each trophic level 80 to 90% of energy is lost. Hence the amount of energy decreases from the producer level to the consumer level. This can be represented in a pyramid of energy level to the consumer level. This can be represented in a pyramid of energy. Succession
(1) Every community undergoes a series of changes until a group of organisms established
which can live and reproduce most successfully in the area. This is called biotic succession.
(2) The term succession was coined by Hult (1885).
(3) A biotic community normally undergoes continuous changes. Generally, definite and orderly sequences of communities gradually appear in an area over a period of time.
(4) A specific sequence of development of a community is related to particular set of physical
and chemical conditions. This is known as sere.
(5) The last succession in a series is called climax or a climatic climax.
(6) Types: Succession is of two types:
(i) Primary succession: It includes changes which occur when living things become established on a previously uninhabited area such as a newly exposed sea floor, lake sediments or sand dunes.
(ii) Secondary succession: It occurs where early communities have been damaged, leaving a
few organisms and considerable organic matter. These remnant species, along with some
new ones, regenerate a new community.
(iii) Life forms: Raunkiaer (1934) has distinguished plants into five forms on the basis of size,
shape, branching, crown, life span and perennation.
(a) Therophytes: Annual plants which perennate in the form of seeds.
(b) Cryptophytes: Buds occur very deep in the soil e.g. Bulbs, rhizomes, corm, tubers etc.
(c) Hemicryptophytes: Perennating structures occur at ground level. Aerial shoots die in the onset of winter, e.g. rosette plants.
(d) Chamaephytes: Small plants of cold areas where perennating buds or shoot apices lie at
or above the ground level.
(e) Phanerophytes: Perennial herbs, shrubs and trees, epiphytes, succulents, lianas, etc.,
where perennating buds occur at 10 cm or more height above ground level.
Nutrient Cycling
Carbon Cycle
(1) The cycling of carbon between biotic and abiotic systems is called the carbon cycle. It is a
gaseous cycle.
(2) The main source of carbon is carbon dioxide (CO₂).
(3) CO, is present in the air and water. Air is the main reservoir. CO, content of air is 0.03%. Its amount remains constant.
(4) Flow of Carbon into the biotic system: Carbon flows into the biotic system two ways:
(i) Photosynthesis:
6CO₂ + 6H₂O® C6H12O6+60
(ii) Formation of shell:
The CO₂, dissolved in seawater, is utilized by marine animals like protozoans, corals, molluscs, algae, etc., for the construction of shells. In these animals CO is converted into calcium carbonate (CaCO3) which is used for the construction of shells.
CO₂ + H₂O -> H₂CO3 (Carbonic acid)
H₂CO3 -> H + HCO3 (Bicarbonate)
HCO3 + Ca+ -> H+ + CaCO3 (Calcium carbonate)
(5) Flow of Carbon into the abiotic system: The carbon of the biotic system flows into the abiotic system in five ways:
(i) Respiration: Plants and animals release CO, by respiration (biological oxidation).
C6H12O6 = CO+ H₂O + Energy
(ii) Decomposition: When plants and animals die, the dead bodies are decomposed into CO, by decomposers like bacteria, algae, etc..
(iii) Shells: After the death of marine animals, CaCO, stored in the shells is either deposited as
sedimentary rocks or dissolved in water to release CO, by the reversion of the above said reactions..
(iv) Coal: A certain proportion of carbon from plants is deposited as coal. Carbon from coal returns to air in the form of CO, through combustion and weathering.
(v) Forest fire: Combustion of wood in the forest releases carbon from plants in the form of CO₂.