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AP Enviro



Unit 3

3.8 Human Population Dynamics

2 min readmay 1, 2020

Karla Jauregui Sandoval


Image Courtesy of Pixabay

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 healthier life. 

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, the tsunami that hit Japan in 2011 killed people regardless of the population size. 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. 

Population Formulas 

  1. Annual Percent Change ➪ this formula is used to calculate the change in population 


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