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Density-Independent Factors: Examples, Definition & Quiz

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Taught by

Derrick Arrington

Derrick has taught biology and chemistry at both the high school and college level. He has a master's degree in science education.

Many things can limit the size of a population of organisms. In this lesson we will explore density-independent factors to gain an understanding of what they are and how they work on populations.

Definition of Density-Independent Factors

Both living and non-living things can influence the size of a population of organisms. Some things that happen to populations such as disease and parasites depend on the size of the population to be successful at causing destruction. Things and events that limit the size of a population regardless of the density of the population are called density-independent factors.

The density of a population can be described as the number of organisms living in a specific area at a certain time. For example, a field with thousands of corn plants is much more densely populated than a field of the same size with an orchard of forty fruit trees. Density-independent factors can affect a population of organisms no matter how small or large the population may be.

Examples of Density-Independent Factors

Most density-independent factors are abiotic, or nonliving. Some commonly used examples include temperature, floods, and pollution.

How could temperature be a factor in determining the density of a population? Imagine a heavily forested area that is home to a population of mosquitos. It is well known that mosquitos cannot survive in very cold temperatures. If a large cold front suddenly comes through the area and causes the temperature to drop it would kill the entire population. It would not matter if there are ten mosquitos or ten thousand the cold weather would affect them all. This makes it a density-independent factor because population density does not matter.

Changes in temperature such as cold fronts are density-independent factors.
A picture of snowy weather.

You have probably seen earthworms before and know that they live their entire lives burrowing through the soil. It is also important to know that they cannot live in water. For this reason, you may see them on the ground after a large rain storm. Imagine if a flood strikes an area inhabited by earthworms. It would damage the entire population in the flooded area. It is important to note that it would make no difference if the population is extremely large or very small. This makes an extreme weather event such as a flood a density-independent factor.

Earthworms like this cannot survive a density-independent factor such as a flood.
Image of an earthworm.

All forms of pollution can act as density-independent factors. Once a pollutant enters the environment it can have an effect on all organisms living there. It doesn't matter if the populations are large or small - in either scenario, they can be affected negatively by the pollution.

Summary of Density-Independent Factors

When you are trying to decide whether or not something is a density-independent factor you must determine if its effect depends on the size, or density of the population. If it affects the population regardless of the population density it is a density-independent factor.

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