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Adisturbance event perturbs ecosystems, driving ecological patterns and processes outside their normal range of variability. Disturbances may alter species richness, population structure, net primary production, and nutrient flows. These changes may be temporary or long term, depending on both disturbance type and ecosystem characteristics. Determining whether ecological changes fall within normal ecosystem variability requires a judgment call. When is drought severe enough to be a disturbance? When does insect herbivory grade into insect outbreak?

Anthropogenic disturbances are caused by people, and include fire, oil spills, livestock grazing, pollution, logging, and fishing. Natural disturbances are caused by climatic, geologic or biological change. Examples of climatic disturbances are drought, hurricanes, and windstorms. Geologic events include earthquakes, volcanic eruptions, and landslides. Pest or pathogen outbreaks, mass marine mortality, and ...

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