The major causes of change in population size are

The major causes of change in population size are births, deaths, and migration. Births increase the population size by adding new individuals to the population. Deaths decrease the population size by removing individuals from the population. Migration can increase or decrease the population size depending on whether people are moving in or out of the area. Overall, population size is influenced by the balance between births, deaths, and migration. If the number of births is greater than the number of deaths and migration, the population will increase. Conversely, if the number of deaths and migration is greater than the number of births, the population will decrease.