Explain how population structures change at Different stages of the D.T.M (15)

The population structure for stage 1 of the D.T.M (high fluctuating) has a low height, concave sides and uneven distribution of age groups. Birth rates are relatively constant and high but epidemics, famines and conflicts lead to fluctuations in death rates. These affect some age groups more than others in an erratic way. This structure is restricted to only a few of the world’s poorest peoples such as tribes in the Amazonian rainforest.

Stage 2 (early expanding), however, sees a broad base with steep not concaving sides. It also has a higher top, although still narrow. The spread of modern medical science and improvements in public health have lead to a fall in death rate. The wide base reflects a remaining high birth rate due to the socio-economic conditions. Here the young make up the largest percentage and dominate the age structure. In some countries, such as Chad, the under 15 population make up to 50% of the total population.

Stage 3 is known as the late expanding stage. In this population pyramid there us a narrower base as the birth rates are staring to decline. There is also a broader top as the life expectancy rises and the slides are slightly convex. Overall, improved standards of socio-economic conditions have led to a better quality of life and a reduction in family sizes as women often discover other roles to motherhood. The marked feature is the bulge in age groups among those of working age born when birth rates were higher. This structure is typical of countries such as India and Brazil who have recently undergone industrialisation.

Stage 4, of which Britain belongs, shows a low fluctuation of birth and death rates. There is a narrow base and straight sides due to the least amount of variation in size between the different age groups. The top is broad which again shows the increase in life expectancy.

Finally, stage 5 starts to see a top heavy population pyramid where the fertility rate has fallen below 2.1 and the population will not replace itself. There is a very narrow base which means the country is in decline. There tends to be older women than men which makes the pyramid uneven.