Ecological Pyramids

Ecological Pyramids of Numbers, Biomass and Energy

An ecological pyramid shows the relationship of biomass, productivity or energy at different trophic levels. The primary producers are generally shown at the bottom and apex predators at the top. The pyramids are different for different ecosystems. There are three types of Ecological Pyramids as follows:
Pyramid of numbers: This shows the number of individual organisms at successive trophic levels. It can be upright or inverted.

Pyramid of Biomass: This shows the biomass at successive trophic levels. It can be upright or inverted.
Pyramid of energy: It shows the rate of energy flow and/or productivity at successive trophic levels. It is always upright.

1. Pyramid of Numbers

2. Pyramid of Biomass

3. Pyramid of Energy

Pyramid of Numbers

This Pyramid shows the numbers of the producers, herbivores and the carnivores at their successive trophic levels. This pyramid can be either upright, or inverted or partially upright.
Pyramid of numbers in grassland Ecosystem

In a grassland ecosystem, the number of producers (mainly grasses) is always maximum, followed by decreasing numbers at second trophic level (herbivores), third trophic level (carnivores) and least number of apex predators. Thus, a pyramid of numbers in grassland is upright.

Pyramid of Numbers in Pond Ecosystem

In a pond ecosystem, the producers are phyto-planktons such as algae, bacteria etc. They are maximum in number. The small herbivorous fishes, rotifers etc. are smaller in number than producers , while the small carnivorous fishes are even less in number. Finally, the apex consumers or biggest carnivorous fishes are least in number. Thus, the Pyramid of numbers in a Pond Ecosystem is also upright.
Pyramid of Numbers in Forest Ecosystem

In a forest ecosystem, the producers are large size trees which make the base of Pyramid. The herbivores such as fruit eating birds, deer, elephants etc. make the primary consumers and are less than primary producers. After that, the number goes down at each successive level. Thus, a Pyramid of numbers in a Forest Ecosystem is partially upright or spindle shaped.

Pyramid of Numbers in Parasitic Food Chain

A single plant or animal in a parasitic food chain may support numerous parasites, which might be further supporting a larger number of hyperparasites. Thus, the pyramid of numbers in a parasitic food chain is inverted.

Pyramid of Biomass
Pyramid of Biomass in Forests and Grasslands

Pyramid of biomass for terrestrial ecosystems (grasslands, forests) the biomass generally decreases at each higher trophic level from plants via herbivores to carnivores. This is evident from the fact that the terrestrial producers’ viz. grasses, trees and shrubs have a much higher biomass than the animals that consume them, such as deer, zebras and insects. The level with the least biomass is the highest predators in the food chain, such as foxes and eagles. Thus, in terrestrial ecosystems, the Pyramid of Biomass is upright.

Pyramid of Biomass in Aquatic Ecosystems

In the aquatic system, the biomass can increase at higher trophic levels. For example, in Oceans, the food chain typically starts with phytoplankton and ends at predatory fish, which has largest biomass. Thus, the pyramid of biomass is inverted in the aquatic systems including marine, ponds etc.

Pyramid of Energy

Energy cannot be recycled and during the flow of energy from one trophic level to other, there is a considerable loss in the form of heat, respiration, mechanical energy etc. Thus, highest energy is available to primary producers and lowest to tertiary consumers. Thus, the pyramid of energy is always upright and vertical. In this pyramid, the energy is minimum as the highest trophic level and is maximum at the lowest trophic level.

Since there is a successive reduction in energy flow at successive trophic levels, shorter the food chain, greater would be the available food energy. The reason is with an increase in the length of food chain, there is a corresponding more loss of energy.



1.) With reference to food chain, consider the following statements:

1.Only 10 per cent of the energy is transferred to each trophic level from the lower trophic level.
2. The flow energy takes place in both directions in food chain.
3. The natural interconnection of food chains makes it a food web.

Which of the statements given above is/are correct?

(a) 1 and 2 only
(b) 2 and 3 only
(c) 1, 2 and 3
(d) 1 and 3 only

Answer .d

2.) The base of Ecological pyramid represents the ______ or the first trophic level while the apex represents______ or top level consumer.

(a)producers, tertiary
(b) tertiary, producers
(c) herbivore, carnivore
(d) carnivore, herbivore

Answer .a

3.) Choose the false statement among the following statements:

(a) The pyramid of biomass in sea is also generally inverted because the biomass of fishes far exceeds that of phytoplankton.
(b) Pyramid of numbers in a grassland ecosystem is inverted.
(c) Pyramid of energy is always upright, can never be inverted.
(d) Ecological pyramid does not take into account the same species belonging to two or more trophic levels. It assumes a simple food chain, it does not accommodate a food web.

Answer .b

4.) The gradual and fairly predictable change in the species composition of a given area is called as _______ .

(a) Ecological succession
(b) Ecological balance
(c) Ecological stabilization
(d) Stabilization of the species

Answer .a

5.) Consider the following statements:

1. With respect of succession of plants; Hydrarch succession takes place in wetter areas and xerarch succession takes place in dry areas.
2. The species that invade a bare area are called pioneer species.
3. All communities composition and structure constantly change in response to the changing environmental conditions. These changes lead finally to a community that is in near equilibrium with the environment and that is called a climax community

Which of the statements given above is/are correct?

(a) 1 and 2 only
(b) 2 and 3 only
(c) 1, 2 and 3
(d) 1 and 3 only

Answer .c

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