A keystone species is one that plays a key role in the ecosystem, affecting may other species, and whose removal leads to a series of extinctions within the system – extinction cascade. Top predators are often considered keystone species. For instance, the sea otter is a keystone species found throughout the Pacific that feeds on shell fish. Hunting them increases the population of shellfish, which in turn, decreases the abundance of kelp, since shellfish feed on kelp, which help to reduce the impact of waves and current. Therefore, the sea otter plays a key role in the ecosystem by keeping the shellfish population in check. Ecosystem engineers, such as the dung beetle and beavers, are also considered keystone species. Without keystone species, the ecosystem becomes degraded with low biodiversity at all tropic levels.
Similarly, keystone resources are small physical or structural, mostly nonliving components of a habitat that is crucial to species/community survival. Keystone resouces maintain many animal populations, and their loose could result in the rapid loss of animal species, such as birds and mammals – leading to an extinction cascade. An example of a keystone resource would be salt licks and mineral pools that animals depend on during heavy rainfall. Their distribution can determine the abundance and distribution of vertebrates. Other examples include: deep pools, hollow tree trunks, and rotting wood.
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