Types of Ecosystem productivity Explained

 

             Defination 

The productivity of an ecosystem refers to the rate of conversion of energy in an ecosystem into organic matter.

It is often measured in tons, grammes or kilocalories of energy per unit area on an annual basis (per year).

The higher the productivity of an ecosystem, the greater would be the biomass of an ecosystem and vice versa. However, productivity which is a "rate" should not be confused with biomass which is the total mass of living organisms by dry weight in an area.

             Types of productivity 

Energy can be converted into living matter primarily by plants (producers) and secondarily by animals (consumers). 

On this basis, two main types of production have been distinguished. These are primary and secondary productivity.

1. Primary productivity.

It is the rate of creation of organic matter by producers or green plants per unit area and time. This is achieved through photosynthesis. For this reason, it can also be defined as the rate photosynthesis  in a given area or the rate of energy fixation by plants in a given community.

There are 2 sub types of primary productivity:

Gross primary productivity (DPP) and Net primary productivity (NPP).

-Gross primary productivity: 

It is the total amount of organic matter or energy made by plants, that's the total amount of photosynthesis per unit  area and time. 

Usually, some of the organic matter  created is used as energy by plants for their life processes  and the waste is lost through respiration. The total energy produced minus the one used by plants is called net primary.

-Net primary productivity: 

It can be defined as the amount of energy that is left after losses through respiration of plants. It is the net accumulation or increase of energy. It appears also as an increase in the living weight of plants and by extension can be considered as an increase in the biomass in an ecosystem.

NPP is the energy or matter in plants which is available for primary consumers. It is measured by subtracting used energy (respiration) from GPP.

             GPP- Respiration= NPP (kcl/m2/year)

2. Secondary productivity.

It is the energy converted into living matter by animal's.

This is the second major type of productivity which is carried out by consumers or heterotrophic organisms. 

Variations in Ecosystem productivity

Productivity varies from one place to another. This is largely due to differences in the availability and supply of the elements necessary for the production of organic matter. These include differences in the supply of nutrients, moisture, temperature  and light energy over the earth's surface. At a global scale, contrast can be made between aquatic and terrestrial ecosystems. Generally, terrestrial ecosystems have higher productivity because of the availability of nutrients stored in soil, more plants or photosynthesis than aquatic ecosystems.
The latter has little or no soil to store nutrients, little photosynthetic surfaces and most are saline. However, differences also exist within each of the aquatic and terrestrial ecosystems.
For aquatic ecosystems and within the ocean, the production of the ecosystem tends to vary depending on

• Water depth
• Water freshness 
• Proximity to land from where nutrients are washed to the adjacent waters.

There is a general decline in productivity from the coast towards the open ocean. Estuaries, which are swampy  low lying areas at the mouths of rivers into the sea, have high productivity because of the availability of nutrients washed from surrounding lands and constant input of fresh water which help to reduce salinity. Moreover,sunlight needed for photosynthesis easily penetrates the shallow waters. Together, these account  for the great biodiversity of estuaries with many species of animals and birds. 

The continental shelves also have fairly high productivity because of similar reasons above but not as good as estuaries because of limited supply of fresh water while the open oceans are the least productive because of limited or absence of nutrients, high salinity and very deep waters. 

However, exceptions exist where where certain portions of the open oceans record production. This occurs where there is upwelling of cold bottom waters that bring up nutrients from the sea or ocean bed which together with the available sunlight result in active plankton growth. 

With regard to terrestrial ecosystems, there is a general decline in productivity with some exceptions from the equator towards the poles. The rain forest has the highest productivity (2200g/m2/year) while deserts have the least (90g/m2/year). This explains why there are more kinds of life forms in the tropical rainforest region than in any other terrestrial ecosystem in the world.


To read about the Factors influencing Ecosystem productivity to click READ MORE

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