An ecological pyramid is a graphical model that illustrates the flow of energy through different forms of life in an ecosystem. The bottom level illustrates species which act as producers, harnessing energy from abiotic sources. Each subsequent level illustrates a level of consumer, each of which receives energy by consuming the group below it.
Ecological pyramids are shaped as such to represent the decrease in energy that occurs at each increasing level of an ecosystem. For example, there is more energy contained in producers, which form the base of the pyramid, than in herbivores, which occupy the second widest part of the pyramid.
There are several different ways to present and interpret ecological pyramids. The most common is the type discussed above, in which the pyramid represents energy. A second type of ecological pyramid is used to represent biomass at each level of an ecosystem. Organisms at each level of the pyramid are collected and weighed, and the dry biomass is stated in the pyramid. A third type of pyramid focuses solely on the number of organisms present at each level of the pyramid. The pyramid shape represents the reduction in the number of organisms from the level of the producers to highest-level carnivores.