Ecological Disturbance

Ecological communities constantly change as the number and types of species in a community shift over time.

One major reason for these changes is ecological disturbance, which can be triggered by many different factors.

Natural physical factors, such as drought, can cause ecological disturbances. Biological factors, such as disease, can also disturb an ecosystem. Today, human activities, such as deforestation, create some of the largest disturbances.

These events change the makeup of an ecosystem by adding or removing organisms or by changing the amount of available resources.

The intensity of a disturbance affects how strongly it impacts an ecosystem. For example, a low-intensity storm may damage only a few trees. On the other hand, a high-intensity flood may wipe out many plants and animals in the affected area.

The geographic extent of a disturbance also affects an ecosystem. When a single tree falls, it causes only local damage. But a wildfire can spread across hundreds of miles and affect entire landscapes.

The frequency of disturbance is another important factor. In some ecosystems, a single fire can help a forest recover by promoting regrowth and recycling soil nutrients. Repeated fires can harm the ecosystem. They reduce the time available for native plants to recover and lower soil fertility.

Ecological disturbances influence species diversity in a community. Ecologists have proposed a pattern that helps explain this relationship.

The intermediate disturbance hypothesis states that moderate levels of disturbance can support higher diversity than very high or very low levels of disturbance.

High levels of disturbance can lower diversity because only fast-colonizing species can establish quickly. Slower-growing species do not get enough time to establish.

Low levels of disturbance can also reduce diversity. When disturbances rarely happen, highly competitive species can dominate resources and prevent less competitive species from becoming established.