Population Growth: The change in the size (increase or decrease) of a particular group within an area over time.
Fertility Rate: The average number of children born per woman during her reproductive years. Lower fertility rates contribute to negative natural increase rates.
Life Expectancy: The average length of time an individual is expected to live based on current mortality rates. Higher life expectancy can lead to lower natural increase rates due to longer lifespans and fewer births needed for replacement level.