Environmental Engineering Reference
In-Depth Information
Ecological Pyramids
An
ecological pyramid,
also called an energy pyramid, is a diagram that shows the loss of available energy at
each trophic level. Some energy is transformed into heat, which enters the environment and cannot be used.
Losses may be caused by the incomplete digestion of food, incomplete capture of energy released during cellu-
lar respiration, or degradation of energy into heat energy.
An average energy loss of 90 percent occurs from one trophic level to the next, from the bottom of the pyramid
to the top. That means that of 100 percent of the energy captured in the producers, only 10 percent of it moves
to the primary consumer, and 90 percent is lost. Energy transfer from primary consumer to secondary con-
sumer accounts for another 90 percent loss; thus, the net energy gain to the secondary consumer from the sys-
tem is 1 percent. Transfer from secondary to tertiary consumer results in a 0.1 percent net gain to the tertiary
consumer. This energy is usually measured in kilocalories (kcals). The passing of only 10 percent of energy
from one trophic level to the next is sometimes referred to as the 10 percent rule.
The Pyramid of Energy diagram below shows the trophic levels of an arctic food pyramid which indicates an
organism's energy level of consumption. The numbers indicate the amount of energy available to consumers at
that level. The energy decreases moving up the pyramid due to energy lost. The Pyramid of Biomass represents
the biomass at each trophic level in both a grassland ecosystem and an aquatic saltwater ecosystem. In the
ocean pyramid, the mass of producers in the open ocean may be relatively small compared to consumers. This
is because they grow and reproduce rapidly and are able to produce enough energy to support the species in
higher trophic levels.
