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8.8. Ecological pyramids

Trophic or ecological pyramids

The trophic pyramids or ecological are a graphical representation of the trophic relationships in an ecosystem, which shows how different vary trophic levels according to the energy, the biomass or number of individuals.
In these pyramids, each trophic level is represented by a horizontal bar of the same height, but with a width proportional to the characteristic to be represented. At the base of the pyramid are the producers, in charge of synthesizing organic matter from inorganic matter and the energy of the Sun. Above these are the primary consumers, who feed on the producers, the secondary consumers, who feed on primary consumers, and lastly, tertiary consumers.
There are three types of ecological pyramids:

Pyramids of energy

The energy pyramids represent the energy stored in each trophic level at a certain time and that is available to the higher level. These pyramids are the ones that provide the greatest amount of information about the ecosystem.

They are usually expressed in units of energy per unit area or volume and per unit of time, such as g / m 2 .year, cal / m 2 .year, etc.).

The energy transfer from one level to another is approximately 10%. Much of the energy is used for metabolism .

These pyramids can never be inverted , since the energy of the lower trophic level always has to be greater than that of the upper level.

Pirámides de energía

By Roddelgado (Own work) [CC BY-SA 4.0], via Wikimedia Commons

Interactive activity: Pyramids of energy.

Biomass pyramids

The biomass pyramids represent the amount of biom handle ( organic matter alive or dead) of any trophic level .

It is measured in grams or kilograms of organic matter per unit area or volume. For example, g/m2, kg/ha, etc.

It is possible that some pyramids of biomass are inverted, as for example in an aquatic ecosystem in which the producers represent little biomass but reproduce at high speed.

Pirámides de biomasa

By Roddelgado (Own work) [CC BY-SA 4.0], via Wikimedia Commons

Pyramids of numbers

In number pyramids, each bar represents the number of individuals at each trophic level. Generally, the number of individuals decreases in the upper levels, but we can also find inverted pyramids, such as the numerous aphids that feed on a rose bush. Therefore, this information does not provide much information about the real importance of each organism in the ecosystem.

Pirámides de números

By Roddelgado (Own work) [CC BY-SA 4.0], via Wikimedia Commons