All Subjects



AP Bio



Unit 8

8.4 Effect of Density of Populations

2 min readmay 31, 2020


Caroline Koffke

Density-dependent Factors vs. Density-independent Factors

Populations are often affected by factors that inhibit their ability to continue to survive and reproduce. These factors may be broken into two categories: density-dependent factors and density-independent factors.

Density-Dependent Factors

Density-dependent factors are factors in the environment that affects populations differently depending on the size of the population. As the population size increases, the effects of the density-dependent factors increase as well. Examples of density-dependent factors are access to food, the amount of predators, disease, and migration. 
All of these factors depend on the number of organisms in the population. A small population is less susceptible to a decrease in food than a large population that requires a lot of resources. The density-dependent factor that has the most impact on populations is access to food.

Density-Independent Factors

Density-independent factors are factors in the environment that can affect a population regardless of size. Examples of density-independent factors are weather and climate.
Right now, the warming of the planet is greatly affecting populations, regardless of their size. This warming can lead to a loss of habitat, an inability to adapt to temperatures, and a loss of water or food sources. All of these factors can be devastating to a population.

Carrying Capacity

Both density-dependent and density-independent factors lead to a limit in the number of organisms that can survive in an environment. This limit is known as the carrying capacity.

Image courtesy of WikiMedia Commons.

When carrying capacity is in place, logarithmic growth is no longer possible. Instead, ecologists measure logistic growth. This can be calculated with the following equation:
Ex. In a population of 862 iguanas, the per capita growth rate is 0.05, and the carrying capacity is 1000. What is the change in population after one year?
The population of iguanas increased by 6 in one year.
Watch AP Bio live streams here.


Was this guide helpful?

🔍 Are you ready for college apps?
Take this quiz and find out!
Start Quiz
FREE AP bio Survival Pack + Cram Chart PDF
Sign up now for instant access to 2 amazing downloads to help you get a 5
Browse Study Guides By Unit
Big Reviews: Finals & Exam Prep
Free Response Questions (FRQ)
General Review
Multiple Choice Questions (MCQ)
Unit 1: Chemistry of Life
Unit 2: Cell Structure and Function
Unit 3: Cellular Energetics
Unit 4: Cell Communication and Cell Cycle
Unit 5: Heredity
Unit 6: Gene Expression and Regulation
Unit 7: Natural Selection
Join us on Discord
Thousands of students are studying with us for the AP Biology exam.
join now
💪🏽 Are you ready for the AP Bio exam?
Take this quiz for a progress check on what you’ve learned this year and get a personalized study plan to grab that 5!
Hours Logo
Studying with Hours = the ultimate focus mode
Start a free study session
📱 Stressed or struggling and need to talk to someone?
Talk to a trained counselor for free. It's 100% anonymous.
Text FIVEABLE to 741741 to get started.
© 2021 Fiveable, Inc.