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How do births and deaths change the size of a population?
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population
Graph of the world's estimated human population from 1700 until 2000, with population projections extending until 2100.
In population biology and anthropology, the size of a population changes based on the balance between gains and losses. Births (fertility) and deaths (mortality) are primary drivers of these changes.12
- Population Gain: Births increase the number of individuals in a population. The rate of increase is influenced by fertility, which is the average number of offspring produced by individuals under specific environmental conditions.1
- Population Loss: Deaths decrease the population size. Mortality rates are influenced by factors such as resource availability, environmental stress, disease, and predation.1
- Net Change: The difference between birth rates and death rates is known as the rate of natural increase. When births exceed deaths, the population grows; when deaths exceed births, the population decreases. If these rates are equal, the population remains stable.213
These dynamics are further shaped by the environment's carrying capacity, which limits growth based on available life-sustaining resources. Additionally, in animal populations, migration—immigration and emigration—also plays a significant role in determining total population size.1