Why do high and low levels of disturbance usually reduce species diversity? Why does an intermediate level of disturbance promote species diversity?
A high level of disturbance such as dominancy by certain species causes the extinction of other species, except for some tolerant species. The community with a low level of disturbance allows the dominant species to exclude vulnerable species.
Therefore, the community with an intermediate level of disturbance facilitates diversity by allowing the coexistence of all species.
The factor that alters the availability of resources to organisms is called disturbance. It includes dominant species, natural disasters, and human activities. Large scale, low scale, and intermediate disturbance are the three types of disturbances based on their effects or severity in communities.
The natural part of the community causes disturbance in higher frequencies and results in the destruction of resources and elimination of species. Natural disasters such as storms, drought, forest fire, and volcanoes cause a more significant disturbance.
In the same way, the dominancy of one species, such as human activities or high predation, is also examples of larger-level disturbances.
The low-level disturbances do not allow ecosystem reformation. They eliminate the less competitive species from the dominant species. The low-level disturbances caused by natural events cause patches of destruction.
The intermediate level of disturbance allows the development of tolerance in weak species and increases the recovery rate in community members. Species develop new traits for tolerance or against disturbance, which causes diversity in the community.
Therefore, a moderate level of disturbance is suitable for any healthy ecosystem, which contributes to species diversity.
Figure 24.14 illustrates how a hybrid zone can change over time. Imagine that two finch species colonize a new island and are capable of hybridizing (mating and producing viable offspring). The island contains two plant species, one with large seeds and one with small seeds, growing in isolated habitats. If the two finch species specialize in eating different plant species, would reproductive barriers be reinforced, weakened, or unchanged in this hybrid zone? Explain.
The principle of competitive exclusion states that
(A) two species cannot coexist in the same habitat.
(B) competition between two species always causes extinction or emigration of one species.
(C) two species that have exactly the same niche cannot coexist in a community.
(D) two species will stop reproducing until one species leaves the habitat.
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