An ecological pyramid shows a quantity at each trophic level of a food chain as a horizontal bar. Producers are always at the bottom, with each consumer level stacked above. The width of each bar is drawn to scale, proportional to the quantity it represents.
- Pyramid of numbers: the number of individual organisms at each level.
- Pyramid of biomass: the mass of living material at each level, usually dry mass per unit area (g m−2) at one moment.
- Pyramid of energy: the energy passing through each level per unit area per unit time (kJ m−2 year−1).Pyramids are usually pyramid-shaped because energy is lost at each transfer between trophic levels, so less energy is available to support the level above.Each type gives a different kind of information:
- Numbers are easy to collect but ignore size, so a pyramid of numbers can be inverted.
- Biomass takes size into account but is a snapshot, so it can also be inverted in some ecosystems.
- A pyramid of energy is always upright, because energy is always lost between levels, and it covers a period of time. It is the most accurate type but the hardest to obtain, because the energy content of samples must be found by burning them in a calorimeter.All pyramids simplify ecosystems: they treat each trophic level separately, while many real organisms feed at several levels.
- Pyramid of numbers: the number of individual organisms at each level.
- Pyramid of biomass: the mass of living material at each level, usually dry mass per unit area (g m−2) at one moment.
- Pyramid of energy: the energy passing through each level per unit area per unit time (kJ m−2 year−1).Pyramids are usually pyramid-shaped because energy is lost at each transfer between trophic levels, so less energy is available to support the level above.Each type gives a different kind of information:
- Numbers are easy to collect but ignore size, so a pyramid of numbers can be inverted.
- Biomass takes size into account but is a snapshot, so it can also be inverted in some ecosystems.
- A pyramid of energy is always upright, because energy is always lost between levels, and it covers a period of time. It is the most accurate type but the hardest to obtain, because the energy content of samples must be found by burning them in a calorimeter.All pyramids simplify ecosystems: they treat each trophic level separately, while many real organisms feed at several levels.