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Unit 8

8.4 Effect of Density of Populations

2 min readnovember 30, 2021

caroline-koffke

Caroline Koffke


AP Biology 🧬

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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.
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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:
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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?
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The population of iguanas increased by 6 in one year.

Check out the AP Bio Unit 8 Replays or watch the 2021 Unit 8 Cram

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