Pyramid of Productivity (DP IB Environmental Systems & Societies (ESS))

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