Ecological Pyramids

Ecological pyramids show the relative amounts of a specific component at the different trophic levels of an ecosystem

  • The three main types of ecological pyramids measure species numbers, biomass and energy

Pyramid of Numbers

A pyramid of numbers shows the relative number of organisms at each stage of a food chain

  • These are usually shaped like pyramids, as higher trophic levels cannot be sustained if there are more predators than prey
  • However, the shape may be distorted if a food source is disproportionately large in size / biomass compared to the feeder
    • For example, a large number of caterpillars may feed on a single oak tree and many fleas may feed off a single dog host

Pyramid of Biomass

A pyramid of biomass shows the total mass of organisms at each stage of a food chain

  • These pyramids are almost always upright in shape, as biomass diminishes along food chains as CO2 and waste is released
  • An exception to this rule is found in marine ecosystems, where zooplankton have a large total biomass than phytoplankton
    • This is because phytoplankton replace their biomass at such a rapid rate and so can support a larger biomass of zooplankton

Pyramid of Energy

A pyramid of energy shows the amount of energy trapped per area in a given time period at each stage of a food chain

  • These pyramids are always upright in shape, as energy is lost along food chains (either used in respiration or lost as heat)
  • Each level in the pyramid will be roughly one tenth the size of the preceding level as energy transformations are ~10% efficient

Examples of Ecological Pyramids for a Specific Food Chain

ecological pyramids