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 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 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.
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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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.
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