Pyramid of Numbers

"Pyramid of numbers is the graphic representation of number of individuals per unit area of various trophic levels stepwise with producers forming the base and top carnivores the tip".

Pyramid of Numbers in a Grassland Ecosystem

The shape of the pyramid of numbers vary from ecosystem to ecosystem.

In aquatic ecosystems and herbaceous communities, autotrophs are present in large numbers per unit area. They support a lesser number of herbivores, which inturn support fewer carnivores.

Pyramid of Numbers in a Aquatic Ecosystem

So, the producers are smallest sized but maximum in number while, top carnivores are larger in size but lesser in number, so these cannot be used as prey by another. Hence the pyramid of numbers is upright.

In a parasitic food chain, for e.g., an oak tree, the large tree provides food to several herbivorous birds. The birds support still larger population of ectoparasites leading to the formation of an inverted pyramid.

When a large tree support larger number of herbivorous birds which inturn are eaten by carnivorous birds like falcon and eagle, which are smaller in number, it forms a spindle shaped pyramid.