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Density-independent limiting factors affect all populations in similar ways, regardless of the population size. 
Unusual weather, natural disasters, seasonal cycles, and certain human activities—such as damming rivers and clear-cutting forests—are all examples of density-independent limiting factors. In response to such factors, many species show a characteristic crash in population size. After the crash, the population may soon build up again, or it may stay low for some time.
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For some species, storms or hurricanes can nearly extinguish a population. For example, thrips, aphids, and other insects that feed on plant buds and leaves might be washed out by a heavy rainstorm. Extremes of cold or hot weather also can take their toll on a population, regardless of the population's density. A severe winter frost, for example, can kill giant saguaro cactuses in the Arizona desert. In some areas, periodic droughts can affect entire populations of vegetation. Such events can, in turn, affect the populations of consumers within the food web.
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Environments are always changing, and most populations can adapt to a certain amount of change. Populations often grow and shrink in response to such changes. Major upsets in an ecosystem, however, can lead to long-term declines in certain populations. Human activities have caused some of these major upsets, as you will soon read.
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