28.11
Ecological Disturbance
An ecological disturbance is a temporary disruption in the environment resulting from abiotic, biotic, or anthropogenic factors, causing a pronounced…
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.
View the full transcript and gain access to JoVE Core videos
Q1: What causes ecological disturbances in ecosystems?
Ecological disturbances result from natural physical factors like drought, biological factors such as disease, and human activities including deforestation. These events change ecosystem makeup by adding or removing organisms or altering available resources. Disturbances range from small-scale events like a single falling tree to large-scale incidents affecting entire landscapes.
Q2: How do disturbance intensity and frequency affect ecosystems?
Disturbance intensity determines impact strength; low-intensity storms damage few trees while high-intensity floods devastate many organisms. Frequency also matters significantly. Single fires can promote forest regrowth and nutrient recycling, but repeated fires reduce recovery time for native plants and lower soil fertility, harming ecosystem health.
Q3: What is the intermediate disturbance hypothesis?
The intermediate disturbance hypothesis explains that moderate disturbance levels support higher species diversity than very high or very low levels. High disturbance favors only fast-colonizing species, while low disturbance allows competitive species to dominate and exclude less competitive ones, reducing overall diversity in both scenarios.
Q4: How do disturbances affect species diversity in communities?
Disturbances influence species diversity through their intensity, frequency, and spatial distribution. Moderate disturbances create opportunities for diverse species to coexist by preventing competitive exclusion and allowing slower-growing species time to establish. This relationship is central to understanding community composition and ecosystem stability.
Q5: What biological processes are affected by ecological disturbances?
Ecological disturbances affect key biological processes including mortality, reproduction, movement, and social behavior within populations. Severe disturbances causing high mortality can reduce population size and genetic diversity if recovery time and immigration rates are insufficient. Disturbances also influence genetic drift and migration patterns within populations.
Q6: How do disturbances influence natural selection and evolution?
Disturbances cause variations in the strength and direction of natural selection, leading to unpredictable evolution patterns. The selection process following a disturbance alters the phylogenetic composition of communities. This dynamic relationship between disturbance and selection shapes long-term community structure and species composition.
Q7: Why does geographic extent matter for disturbance impacts?
Geographic extent determines the scale of ecosystem change. A single falling tree causes only local damage to its immediate surroundings, while a wildfire spreading across hundreds of miles affects entire landscapes and multiple communities. Larger disturbances impact more organisms and resources across broader areas.