Migration can Change Population Structure

Young adults tend to move from rural areas to urban areas within a country.

These young adults are of working and reproductive age.

The main reason why these young adults migrate is in search of jobs.

Rural-urban migration.

Whis has an affect on the birth rate of the area as it can increase the number of births - an urban city - meaning that in a villiage the birth rate decreases.

Emigration away from contries that are in later stages of the DTM decreases the poulation of that country.

E.g. elderly people in the UK retiring and moving away.

This reduces the amount of OAP's in the UK, but increases the number of OAP's in the recieving country. 

Immigration from countries in the earlier stages of the DTM (LEDC's), into countries in the later stages (MEDC's), increases population of the reproductive and working age.

Economic-migrant.

This increases the number of young people in the population and also increases birth rate.