- This deals with the relationship between the numbers of primary producers and consumers of different levels.
- It is a graphic representation of the total number of individuals of different species, belonging to each trophic level in an ecosystem.
- Depending upon the size and biomass, the pyramid of numbers may not always be upright, and may even be completely inverted.
a) Pyramid of Numbers – Upright
In this pyramid, the number of individuals is decreased from lower level to higher trophic level.
Example of this pyramid – Pond ecosystem.
Lowest trophic level occupied by snails because of their abundance.
Next higher trophic level – primary consumer – herbivore (example – Small fishes)
Number of small fishes is less than that of snails.
The next energy level is primary carnivore (example bigger fishes).
The numbers of bigger fishes are less than small fishes because, they feed on smaller fishes.
The next higher trophic level is secondary carnivore (example- Crane). They feed on bigger fishes.
With each higher trophic level, the number of individual decreases.
b) Pyramid of Numbers – Inverted
In this pyramid, the number of individuals is increased from lower level to higher trophic level.
Example of this pyramid – A tree in forest ecosystem.
In the above diagram you can see that a big tree (primary producer) supports many birds (herbivores).
These birds eat lots of tapeworms, fleas, and barnacles (parasites) which live on this tree. Number of parasites is more than number of birds.
These parasites eat hyperparasites. Number of hyperparasites is greater than number of parasites.
With each higher trophic level, the number of individual increases and so the resulting pyramid is of inverted shape.
A pyramid of numbers does not take into account the fact that the size of organisms being counted in each trophic level can vary.
It is difficult to count number of trees, birds and grasses etc. so the pyramid of no. doesn’t completely define the trophic structure of ecosystem.
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