- In ecology, productivity refers to the rate at which energy is converted into biomass in a given area over a given time period.
- It measures how efficiently energy from the sun (or chemical sources in some ecosystems) is captured and stored as organic matter.
Gross Productivity (GP)
Gross productivity
Gross Productivity (GP) refers to the total amount of biomass produced by an organism or a trophic level over a given period of time.
- Gross productivity (GP) is the total energy or biomass gained by an organism, population, or ecosystem in a given time period.
- It includes all energy captured, whether used for growth, reproduction, or lost later as respiration.
- In producers, GP represents the total energy captured from sunlight via photosynthesis.
- In consumers, GP represents the total energy assimilated from food intake (food eaten minus energy lost in feces).
$$\text{Gross Productivity (GP)} = \text{Total energy captured or assimilated}$$
ExampleIf aquatic plants in a pond capture 1000 kJ of solar energy through photosynthesis, that is their gross productivity.
AnalogyGP is like your gross salary - the full amount you earn before taxes and expenses.
Net Productivity (NP)
Net productivity
Net Productivity (NP) is the amount of biomass remaining after the losses due to cellular respiration have been subtracted from the gross productivity.
- Net Productivity (NP) is the remaining energy after respiration losses (R) are subtracted from gross productivity.
- It represents the energy available for growth, reproduction, and storage in biomass, and ultimately, the energy available to the next trophic level.
$$\text{NP} = \text{GP} - \text{R}$$
AnalogyNet productivity is like your “take-home pay” - what remains after you’ve paid all your living expenses (respiration).
Net Productivity and Sustainable Yield
Sustainlable yield
The sustainable yield is the maximum amount of water that can be withdrawn from the system without reducing its capacity to regenerate.
- Net productivity of a population or ecosystem determines its maximum sustainable yield (MSY).
