Two main things that decrease a population are:
- Mortality (death rate): The number of deaths in a population over a period of time reduces the population size. Higher death rates, influenced by factors like disease, famine, war, and poor healthcare, decrease population numbers.
- Emigration: The movement of individuals out of a population to another area decreases the population size of the original location. When people leave a region, the population there shrinks.
Other factors influencing population decline include fewer births than deaths (natural decrease), environmental stresses such as food limitation and natural disasters, and social, economic, and political factors causing migration or reduced birth rates.
