Hypothetical Age Pyramids

The three types of hypothetical age pyramids which are as follows:

1) A pyramid with a broad base, indicating a high percentage of young individuals in a population. This shows that population is expanding exponentially.

2) A triangular or bell shaped pyramid indicating moderate proportion of young to old individuals. This is the characteristic of a stable population where natality equals mortality.

3) An urn shaped figure indicating a low number of young individuals. This pyramid is the characteristic of aging or declining population.

Figure: Three types of age pyramid showing large (1) moderate (2) and small (3) number of young individuals in a population. Vole population under laboratory conditions is shown expanding (a), and stable (b) age pyramids.