a) What is an age-pyramid?
b) Name three representative kinds of age-pyramids for human population and list the characteristics for each one of them.

Explanation

a) A population at any given time is composed of individual of different ages. If the age distribution is plotted for the population, the resulting structure is called an age pyramid.
b) For human population, age pyramids generally show age distribution of males and females. The shape of pyramids reflects the growth status of the population.
i) whether it is growing
ii) Stable
iii) declining
The size of the population tell us a lot about its status in the habitat.
a) Expanding populations: In a rapidly growing birth rate is high and population growth may be exponentila, as in the case of the housefly, yeast and algae.
b) Stable population: As the growth rate decreases and stabilizes, the pre-reproductive and reproductive age group become more or less equal in size, the post-reproductive groups, remains as the smallest.
c) Declining: Indicating a low number of young individual.