The size of a population is influenced by a combination of four key factors: birth rate, death rate, immigration, and emigration.
1. Birth Rate: This refers to the number of live births per thousand people in a population over a specific period of time. A higher birth rate contributes to population growth, increasing the total number of individuals in that population.
2. Death Rate: The death rate is the number of deaths per thousand individuals in a population during a certain time frame. A higher death rate can reduce population size, while a lower death rate contributes to population growth by allowing more individuals to survive to reproductive age.
3. Immigration: Immigration is the movement of individuals into a population from other areas. This can lead to an increase in population size, especially if the incoming individuals are able to reproduce and contribute to the gene pool.
4. Emigration: Emigration is the movement of individuals out of a population. This can decrease the size of a population, especially if a significant number of individuals leave and reduce the reproductive potential of the remaining population.
In summary, the interplay of these four factors determines whether a population grows, shrinks, or stabilizes over time. Understanding these factors is essential for ecologists and planners as they manage resources and address issues related to population dynamics.