Aquarium and farm house, are artificial or man made ecosystem. In artificial ecosystem biotic and abiotic component are maintained artificially like cleaning, feeding and supply of oxygen to fishes in aquarium and irrigation in crop or farm house.

While abiotic and biotic component of natural ecosystem are maintained naturally like nutrient cycle, self sutainability, prevention of soil erosion, pollutant absorption and reduction of threat to global warming (ecological servicer), etc.

During ecological succession biodiversity increase or changes from pioneer to climax stages.

Following are the effects of ecological succession

(a) It leads to changes in vegetation that affects food and shelter for various types of animals.

(b) As succession proceeds, the numbers and types of plants, animals and decomposers also change.

(c) At any time during primary or secondary succession, natural or human induced disturbances (fire, deforestation, etc.) can convert a particular seral stage of succession to an earlier stage.

Also such disturbances can create new conditions that encourage some species and discourage or eliminate other species of producer, consumers and decomposers.

(d) Over the time, they are succeeded by bigger plants and, ultimately a stable climax forest community is attained.

(e) The climax community remains stable if the environment remains unchanged.

(f) With time, the xerophytic habitat may gets converted into a mesophytic one.

Biogeochemical Cycle

(i) The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling or biogeochemical cycles (Bio-living; geo-including air, water and rocks).

(ii) Nutrient cycles are of two types

(a) Gaseous

(b) Sedimentary

(iii) Atmosphere is the reservoir for gaseous type of nutrient cycle (e.g., nitrogen and carbon cycle).

(iv) Earth's crust is the reservoir of sedimentary cycle (e.g., sulphur and phosphorus cycle).

(v) The function of the reservoir is to meet with the deficit, which occurs due to imbalance in the rate of influx and efflux.

(vi) Environmental factors, e.g., soil, moisture, pH , temperature, etc., regulate the rate of release of nutrients into the atmosphere.

Phosphorus Cycle

Phosphorus cycle is an example of sedimentary nutrient cycle since, it moves from land and sedimented at the bottom of the seas, then back to land again.

The natural reservoir of phosphorus is earth's crust. Rock contains phosphorus in the form of phosphates. By weathering and soil erosion, phosphates enter streams, rivers and then to oceans.

With great movements of the crustal plates, sea floor is uplifted and phosphates become exposed on the drained land surfaces. From here, weathering over long periods of time releases phosphates.

From rocks, minute amount of these phosphates dissolve in soil and are absorbed by the roots of the plants.

Herbivores and other animals obtain this element from plants when they consume plants as their food.

The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria thus releasing phosphorus.

A simplified model of phosiphorus cycling in a terrestrial ecosystem

Production/Respiration ratio ( $\mathrm{P} / \mathrm{R}$ ) ratio It shows the relationship between gross production and total community respiration where $\mathrm{P} / \mathrm{R}=1$ a steady state community result.

This result may be instantaneously daily one or over a longer period. If $P / R$ is persistantly greater or less than/then organic matter either accumulates or is depleted respectively.

Pioneer Community	Climax Community
The species that invade a base area are called pioneer species on base rockes these are generally lichens.	It is a final biotic community that develops in an area.
In aquatic ecosystem there are phytoplanktons.	It occurs over an area previously occupied by several communities.
In pioneer community the $P / R$ ratio will be more than one.	In climax community the P/R ratio will be 1 .