Density Independent Factors

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A density-dependent factor is one where the effect of the factor on the size of the population depends upon the original density or size of the population. A disease is a good example of a density-dependent factor. If a population is dense and the individuals live close together, then each individual will have a higher probability of catching the disease than if the individuals had been living farther apart. Not only will a greater number of individuals be affected, but, more importantly, a greater proportion of the population will be affected if they are living close together. For example, bird populations are often regulated more by this type of regulation. In general, density-dependent factors are biological factors, such as diseases, parasites, competition, and predation. A density-independent factor is one where the effect of the factor on the size of the population is independent of and does NOT depend upon the original density or size of the population. The effect of weather is an example of a density-independent factor. A severe storm and flood coming through an area can just as easily wipe out a large population as a small one. Another example would be a harmful pollutant put into the environment, e.g., a stream. The probability of that harmful substance at some concentration killing an individual would not change depending on the size of the population. For example, populations of small mammals are often regulated more by this type of regulation. In general, density-independent factors are physical factors, such as weather factors (e.g., severe winter) or the presence of harmful
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