Aquatic ecology and Biodiversity

Unit 2- Ecosystem ecology

2.3.4. Types of ecological pyramids
• Pyramid of Biomass (g /m²/ day)
• Pyramid of Energy (calories)
• Pyramid of Number (No /m²/day)

Pyramid of number
A pyramid of numbers shows the number of organisms at each trophic (relating to nutrition) level. In pyramids of numbers, the number of individuals at the trophic level decreases from the producer level to the consumer level. In an ecosystem, the number of producers is far high and the number of consumers in the subsequent trophic levels are lesser than that of the producers.
Example: In a pond ecosystem, the number decreases in the following order
Phytoplankton → Zooplankton → Small fishes → Large predatory fishes

Pyramid of biomass
Biomass refers to the total weight of living organisms in a unit area. An ecological pyramid of biomass shows the relationship between biomass and trophic level by quantifying the amount of biomass present at each trophic level. In the pyramid of biomass, there will be a clear cut decrease in the biomass from the lower to the higher trophic levels. Generally, the pyramid of biomass is an upright one (the apex is pointed upwards) in all terrestrial ecosystems. In certain ecosystems like pond ecosystem, the pyramid of biomass is an inverted type of pyramid (apex is pointed downwards). In this type of ecosystem, which contain less amount of biomass of producers and more amount of biomass of consumers (fishes).


Example: An Ocean Food Pyramid: It takes about 2500 pounds (1136 kg) of phytoplankton to support 0.5 pound (0.227 kg) of tuna. The decrease from 2500 to 500 is 80 percent. The other trophic levels in this pyramid are decreased by 90 percent. It is an upright pyramid of biomass.

Pyramid of energy
At each trophic level in the food chain, energy that was originally stored by the autotrophic plants is dissipated along the food chain. When the trophic links or levels in the food chain are more, the dissipated or unusable energy loss will also be more. There is generally a 90 percent loss at each level of the food chain, creating a pyramid-shaped diagram that is wider at the bottom and narrow at the top. Example: In a pond, maximum energy is stored by the phytoplankton. Then, the energy decreases when it is transferred to the subsequent consumer levels.