A keystone species is a species that has a very large effect on its environment in relation to its abundance. Translation: a very small number of individuals can cause extreme changes in its environment simply by being there. Examples include sea otters, sea stars (Pisaster ochraceus), tiger sharks, elephants, and the grey wolf. One common aspect of keystone species is that their behavior shapes their environment and increases the number of other species present (increases diversity). Therefore, keystone species are also often classified as indicator species, umbrella species, or ecosystem engineers. Check out what happens when a keystone species goes extinct here.
Indicator species are used to help determine the health of an ecosystem. Often these species will only grow in certain conditions (ie specific temperature, moisture, and levels of chemicals) and are more quickly impacted by pollution. Since these species are sensitive to changes in their environments, they are used as an early warning to indicate that something is different. Examples include crayfish, corals, sea and river otters, and peregrine falcons. Indicator species are used to monitor water quality, changes in ocean temperature, and the presence of pollutants or chemicals.
An umbrella species is a species whose protection will indirectly protect multiple other species in the same ecosystem.
These species are chosen to make it easier to make conservation decisions. Examples include Northern spotted owls, sea otters, whales, and tigers. These species generally have a large habitat and have more requirements for survival than other species that may live in the same habitat. Therefore, by meeting the needs of an umbrella species the needs of several other species are met as well. For example, efforts to protect tigers have simultaneously protected leopards, boars, antelopes, and monkeys.
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