4.1.9 Skills: Pyramids of Energy

• Pyramids of energy illustrate the amount of energy contained within the biomass of organisms at each trophic level
• The length of each box, or bar, represents the quantity of energy present
  • Pyramids of energy should be drawn to scale so that each bar is proportional in size to the amount of energy that it represents
  • In some situations, however, a pyramid of energy may be an approximate sketch where each bar is a rough representation of the energy contained

• These pyramids are always widest at the base and decrease in size as they go up
  • The base is wide due to the large amount of energy contained within the biomass of producers
• Pyramids of energy show a stepped decrease in the energy contained at each level of the food chain rather than appearing as pyramid with smooth sides
• The levels of a pyramid of energy should be labelled producer, first consumer, second consumer, and so on
• The units used should be the amount of energy, per unit area, per year e.g. kJ m^-2 year^-1
• 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
• As a result of this, the biomass at each trophic level will also decrease as energy availability decreases

The energy stored in the biomass of organisms can be represented by a pyramid of energy