An ecological pyramid is a graphical representation of various ecological

parameters such as the number of individuals present at each trophic level, the

amount of energy, or the biomass present at each trophic level. Ecological

pyramids represent producers at the base, while the apex represents the top level

consumers present in the ecosystem. There are three types of pyramids:

$\to$ Pyramid of numbers

$\to$ Pyramid of energy

$\to$ Pyramid of biomass

Pyramid of numbers: It is a graphical representation of the number of individuals

present at each trophic level in a food chain of an ecosystem. The pyramid of

numbers can be upright or inverted depending on the number of producers. For 

example, in a grassland ecosystem, the pyramid of numbers is upright. In this type

of a food chain, the number of producers (plants) is followed by the number of

herbivores (mice), which in turn is followed by the number of secondary

consumers (snakes) and tertiary carnivores (eagles). Hence, the number of

individuals at the producer level will be the maximum, while the number of

individuals present at top carnivores will be least.

On the other hand, in a parasitic food chain, the pyramid of numbers is inverted.

In this type of a food chain, a single tree (producer) provides food to several fruit

eating birds, which in turn support several insect species.

Pyramid of biomass: A pyramid of biomass is a graphical representation of the

total amount of living matter present at each trophic level of an ecosystem. It can

be upright or inverted. It is upright in grasslands and forest ecosystems as the

amount of biomass present at the producer level is higher than at the top carnivore

level. The pyramid of biomass is inverted in a pond ecosystem as the biomass of

fishes far exceeds the biomass of zooplankton (upon which they feed).