(Productivity = rate of production)
There are two types of productivity:
Commonly used productivity unit:
- Primary Productivity: Producer organisms, including both photosynthetic & chemosynthetic, convert radiant energy to organic substances and the rate at which they convert is termed primary productivity i.e. Rate of conversion of radiant energy to organic substances by producers is termed primary productivity.
- Secondary Productivity: Rate of energy storage/production of own biomass by consumers. It is driven by organic substances transferred from lower trophic level.
Primary productivity is divided further into Gross & Net amounts but secondary productivity is not as consumers use food energy already produced with respiratory losses counted and it is directly converted to various tissues by one process.
Primary Productivity is divided into –
- Gross Primary Productivity (GPP) (Total Photosynthesis): Rate at which chemical energy is created by producer. It includes the energy used up in respiration i.e. total rate of photosynthesis along with the organic matter used for respiration.
- Net Primary Productivity (NPP) (Net Assimilation): Rate of storage of chemical energy in producer, which exceeds the respiratory use. NPP is directly available for growth & development of the producer.
For an entire ecosystem
Other important points:
- Difference between Biological ‘Productivity’ & Industrial ‘Yield’
- In Industry, a reaction ends up with production of a given amount of substance (yield).
- In Biological Community, production process is continuous in time (Productivity). Therefore, a time unit must be mentioned for productivity.
- Biomass or Standing Crop should not be confused with productivity.
- By simply counting/censusing/weighing organism at a unit time, usually one cannot primary productivity of the system or production of a population. Though Net Primary Productivity can be estimated from standing crop when living material accumulates over time without being consumed (e.g. in cultivated crops).
- Human increase in food production does not necessarily involves increase in gross productivity.
- Percentage of Gross Primary Productivity:
- Highest at: Cold Latitudes
- Lowest at: Hot Latitudes
- Reason: More respiration required to maintain biomass in hot latitudes.
Energy Flow Models
To be continued…