28.11
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.
生态扰动是非生物、生物或人为因素造成的环境暂时破坏,导致生态系统发生明显变化。生态扰动的影响取决于其强度、频率和空间分布,在形成生态系统内的物种多样性方面起着重要作用。
生态扰动可能由像森林火灾或洪水那样小而小的踩踏到范围广泛的事件造成的。火山和飓风等自然事件、放牧和虫害爆发等生物干扰以及森林砍伐等人类活动都可能导致生态扰动。
生态系统中种群中的关键生物过程,如死亡率、生殖、运动和社会行为,都可能受到干扰的影响。如果人口恢复时间和移民率在事件发生后,导致高死亡率的严重干扰会减少人口数量,导致遗传多样性的丧失。干扰还通过影响遗传漂移和迁移来影响种群内的遗传分化。
生态扰动导致自然选择的强度和方向变化,导致不可预知的进化模式。因此,干扰后的选择过程可以改变群落的植物遗传组成。
中间扰动假说指出,当扰动既不罕见也不频繁时,生态扰动会导致物种多样性最大。最高多样性发生在中度干扰水平,其特点是中等强度和频率水平。
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.
From Chapter 28:
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