Question

In a tree ecosystem, it is observed that several insects feed on a single large tree. These insects are eaten by small birds, which in turn are eaten by larger birds. Which of the following shapes represents the pyramid of numbers for such an ecosystem?

• A.
• B.
• C.
• D. both a and b

Answer 1

The correct option is B

Graphic representation of ecological parameters (number, biomass or energy) in various trophic levels of a food chain are called ecological pyramids.

The first trophic level, i.e., producers form the base of the pyramid whereas the topmost trophic level of tertiary consumers (top carnivores) forms the apex.

The pyramid of numbers is a diagrammatic representation of the number of organisms belonging to each trophic level.

Based on their shape, pyramids can be upright (broad base and narrow apex), inverted (narrow base and broad apex) or spindle shaped (broad in the middle and tapering towards the base and apex).

Here, option a represents an upright pyramid, option b represents a spindle shaped one and option c represents an inverted pyramid.

The pyramid of numbers for a tree ecosystem will be spindle-shaped. This is because a big tree (producer) supports a large number of insects which are fed upon by a much smaller number of birds. The top carnivores or the larger birds which feed on these small birds are even smaller in number. This gives the pyramid of numbers a spindle shape.