Pyramids of Productivity
- Pyramids of productivity show the flow of energy through trophic levels, indicating the rate at which that energy is being generated
- Pyramids of productivity illustrate the amount of energy or biomass of organisms at each trophic level per unit area per unit time
- Productivity is measured in units of flow
- The units are mass or energy per metre squared per year (g/kg m-2 yr-1 or J/kJ m-2 yr-1)
- The length of each box, or bar, represents the quantity of energy present
- These pyramids are always widest at the base and decrease in size as they go up
- This is because pyramids of productivity for entire ecosystems over a year always show a decrease along the food chain, following the second law of thermodynamics
- The base is wide due to the large amount of energy contained within the biomass of producers
- As you move up the pyramid to higher trophic levels, the quantity of energy decreases as not all energy is transferred to the biomass of the next trophic level (roughly 10 % of the energy is passed on)
- Energy is lost at each trophic level due to:
- Incomplete consumption
- Incomplete digestion
- Loss of heat energy to the environment during respiration
- Excretion of the waste products of metabolism e.g. carbon dioxide, water, and urea
The energy stored in the biomass of organisms can be represented by a pyramid of productivity
