An ecological pyramid is a graphical representation designed to show the number, biomass and energy at each trophic levels of an ecosystem.
- It represents the trophic structure and function of ecosystem
- First Described by Charles Elton in 1927
- Also called as Eltonian pyramid, trophic pyramid, energy pyramid or food pyramid
- In ecological pyramid, producers form the base and top consumers at the apex
Three types of ecological pyramids are
1. The Pyramid of numbers
2. The pyramid of biomass
3. The pyramid of energy
1. The Pyramid of numbers
The pyramid of number is a graphical representation to show the number of organisms at each trophic levels of an ecosystem.
a) Upright pyramid: In majority of ecosystems, the pyramid is an upright pyramid
The number of individuals at the trophic level decreases from the producer level to the top carnivores. Therefore, the base of the pyramid is broad and apex is pointed.
The number of producers is high followed by herbivores then small number of carnivores.
- Pyramid of numbers in different ecosystem
- In cropland ecosystem: Crops-->Grasshoppers-->Frogs--->Snakes---> Hawks
- In grassland ecosystem: Grasses-->Rabbit-->Fox--> Lion
- In pond ecosystem: phytoplanktons-->Zooplanktons-->Small fishes--> Large fishes
b) Inverted pyramid of numbers: In some ecosystem, the number of individuals at the trophic level increases from the producer level to the top carnivores. Therefore, the base of the pyramid is pointed and apex is broad forming an inverted pyramid
Eg: Tree ecosystem and parasitic food chains:
- Single tree--->many fruit eating birds---> numerous parasites on birds
2. The Pyramid of Biomass
- Biomass is the total dry weight of organisms in a given area
- Expressed in joules per m2 or tonnes per hectare
The pyramid of biomass is a graphical representation designed to show the biomass of organisms at each trophic levels of an ecosystem.
a) Upright pyramid of biomass:
In forest and grass land ecosystem, the biomass decreases from lower to higher trophic level. So the pyramid of biomass is upright
- In grassland ecosystem: Grasses-->mice-->snakes--> hawks
- In forest ecosystem: plants (trees)-->rabbit-->Fox--> Lion
b) Inverted Pyramid of Biomass: In pond ecosystem, the biomass of phytoplankton is very low compared to zoo plankton which is lower than small fishes and large fishes. The biomass increases from the producer level to the top carnivores. Therefore the base of the pyramid is pointed and apex is broad.
- In pond ecosystem: Phytoplanktons-->Zooplanktons-->Small fishes--> Large fishes
3. The Pyramid of Energy
A graphical representation of the energy level and energy flow in different trophic levels of an ecosystem.
- Expressed in Kcal/m2/year
- In an ecosystem, energy flows from producer level to the consumer level
- At each trophic level, 80-90% of energy is lost.
- Energy flow is always uni-directional.
- Pyramid of energy is always upright as energy always decreases from lower to higher trophic level. See Lindmanns 10% law
- Maximum amount of energy is available for producer.