# 3.8 Human Population Dynamics

Karla Jauregui Sandoval

### AP Environmental Science♻️

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Humans experience population growth or decline through infant mortality rates, birth rates, immigration, emigration and the development of a country. Factors that go into a population declining or increasing are access to family planning, nutrition, education and jobs.
Industrialization enabled the human population to grow because there was an increase in sanitation, food and medicine. These basic needs allowed people to live a longer and healthier life.
Human populations continue to change with global trends and patterns, as well as progress. It is important to note that many countries have had improvements with infant mortality rates, as well as general societal improvements, over recent years. Human population dynamics, though, continue to evolve, and are sometimes predictable.

## Rule of 70

A way to predict the doubling time of a population size is by the rule of 70. This rule states that dividing the number of 70 by the percentage population growth rate approximates the population doubling time.
Just like there is a carrying capacity for smaller habitats, Earth also has a limit of finite resources which can support
Example: A population of birds on a small island has an annual population growth of 2.5%. What is the doubling time for the population ?

## Limiting Factors on Population Growth

There are two types of factors that can limit population growth - density independent and density dependent.
A density independent factor is a limit on population growth regardless of population density (size). Some examples of density independent factors are weather, climate, storms, fire, heatwaves, or droughts. For example, a tsunami is not preventable and can not be controlled by competition with resources.
However a density dependent factor is affected by the size of a population. Some density dependent factors are access to clean water, air, food availability, disease, and territory size. These factors cause damage dependent on how many individuals are affected by them.

## Population Formulas

1. Annual Percent Change - this formula is used to calculate the change in population
2. Population Growth Rate - this formula calculates the rate at which a population grows.
Population growth rate = (final population size - initial population size) / initial population size
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