(i) Age Pyramids When the age distribution (per cent individuals of a given age or age group) is plotted for the population, this is called age pyramid, (ii) Population at any given time is composed of individuals of different ages. For human population, the age pyramids generally show age distribution of males and females in a combined diagram. The shape of the pyramids reflects the growth status of the population that whether it is expanding (triangular-shaped), stable (bell-shaped) or declining.
(a) Expanding or Triangular Age Pyramid
In this, number of pre-reproductive individuals is very large, number of age reproductive individuals is moderate, while post-reproductive individuals are fewer. This type of age pyramid shows that population is growing. The rate of growth depends upon the size of pre-reproductive population. This type of population growth is observed in developing countries like India, Brazil.
(b) Stable or Bell-shaped Age Pyramid In this, the number of pre-reproductive and reproductive individuals is almost equal. Post-reproductive individuals are comparatively fewer. The population size remains stable, neither growing nor diminishing. This type of population growth.is observed in countries like USA, Denmark.
(c )Declining or Urn-shaped Pyramid The proportion of reproductive age group is higher than the individuals in pre-reproductive age group. The number of post-reproductive individuals is also sizeable. It is declining or diminishing population with negative growth. This type of population growth is observed in countries like Japan.
