An ecological pyramid, also known as a trophic pyramid or energy pyramid, is a graphical representation designed to show the biomass or bioproductivity at each trophic level in a given ecosystem. Trophic levels refer to positions in the food chain or the successive stages of eating and being eaten. There are three main types of ecological pyramids:
1. Pyramid of Numbers: This represents the number of individual organisms at each trophic level. For example, a grassland ecosystem might have a large number of grasses as producers, fewer herbivores that feed on the grass, and even fewer predators that feed on the herbivores. However, in some cases, like parasitic food chains, the pyramid of numbers can be inverted.
2. Pyramid of Biomass: This represents the total mass of living matter at each trophic level. Generally, the biomass decreases as one moves up the pyramid because energy is lost at each trophic level due to respiration, waste, and other processes. This often forms a true pyramid shape in terrestrial ecosystems, but in aquatic ecosystems, it can sometimes be inverted. For instance, the biomass of phytoplankton (primary producers) in the ocean might be less than the biomass of zooplankton at certain times because the phytoplankton are rapidly consumed by the zooplankton, and their biomass turns over quickly.
3. Pyramid of Energy: This shows the total amount of energy available at each trophic level. Energy is typically measured in units of joules or calories. This pyramid is always upright since energy always decreases as it moves up the trophic levels. This is due to the fact that when organisms consume food, not all of the energy in the food is converted into body mass; much is lost as heat and in metabolic processes. The 10% rule is a general guideline which suggests that only about 10% of the energy from one trophic level is transferred and incorporated into the next level.
Ecological pyramids help ecologists and researchers understand the flow of energy and resources through ecosystems, and they highlight the foundational role of producers and the diminishing energy and biomass available at higher trophic levels.