Phytoplanktons form the pioneer community and a variety of trees makes the climax community of a Hydrosere.

Ecosystem is damaged by disturbances from fire, flood, predation, infection and drought, etc., removing a great amount of biomass. However, ecosystem is endowed with the ability to resist the damage and recover quickly. This ability of ecosystem is called ecosystem resilience or ecosystem robustness.

A graphical representation of the amount of organic material (biomass) present at each successive trophic level in an ecosystem is called pyramid of biomass.

(a) The first link of grazing food chain is plants (Producers).
(b) The first link of detritus food chain is dead remains and excreta of plants and animals.

(a) Grazing food chain
(b) Detritus food chain

First law of thermodynamics states that energy can be transmitted from one system to another in various forms. Energy cannot be destroyed or created. But it can be transformed from one form to another. As a result, the quantity of energy present in the universe is constant.

The transfer of energy in an ecosystem between trophic levels can be termed as energy flow. It is the key function in an ecosystem. Energy flow is always unidirectional in an ecosystem.

(a) Productivity
b) Energy flow
(c) Decomposition
(d) Nutrient cycling

The rate of biomass production per unit area in a unit time is called productivity. It can be expressed in terms of gm /m² /year or KcaVm²/ year.

Grey carbon - carbon stored in fossil fuel (coal, oil and biogas deposits in the lithosphere).
Black carbon - carbon emitted from gas, diesel engine and coal fired power plants.

(a) Climatic factors: Light and Air.
(b) Edaphic factors: Soil and pH of soil.

If all producers are removed from ecosystem We tend to face the following hurdles.
(i) The Ecosystem cannot be balanced
(ii) The interlocking pattern of food chain is broken
(iii) The movement of energy transfer among the food chain cannot be established
(iv) As the green plants occupying the first trophic level (T₁) are producers - it affects majority of the food chain

There is a gradual decrease in energy transfer at successive tropic levels from producers to higher levels, hence the pyramid of energy is always upright.

Because there is no effective light penetration & predominance of heterotrophs.

Gross Primary Productivity (GPP) is the total amount of food energy or biomass produced in an ecosystem by autotrophs through the process of photosynthesis whereas Net Primary Productivity (NPP) is the proportion of energy which remains after respiration loss in the plant. When we compare GPP with NPP more energy is present in former than in latter.