The diagram shows a pyramid of numbers in a food chain. What type of organism is a caterpillar?

The relationship in an ecosystem can be depicted in

$A$: Ecological pyramids cannot explain all the vital functions of any ecosystem.
$R$: Pyramids actually do not explain the role of organisms working at more than one trophic level.

An inverted pyramid of $...A...$ may occasionally be observed in $...B...$ communities.

What type of ecosystem is represented by the given ecological pyramid?

What are the three types of ecological pyramids? What information is conveyed by each pyramid with regard to structure, function, and energy in the ecosystem?