keystone species

[ kēstōn′ ]

A species whose presence and role within an ecosystem has a disproportionate effect on other organisms within the system. A keystone species is often a dominant predator whose removal allows a prey population to explode and often decreases overall diversity. Other kinds of keystone species are those, such as coral or beavers, that significantly alter the habitat around them and thus affect large numbers of other organisms. Compare indicator species.



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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


What does keystone species mean?

A keystone species is a species of plant or animal that most or all of the other species in an ecosystem are directly or indirectly dependent on. If a keystone species were removed from its ecosystem, that ecosystem would change dramatically.

A species is a category of similar living things that can breed with each other (ducks, owls, and eagles are different species of birds for example). A keystone is something that other things depend on.

Keystone species isn’t an official designation and scientists often disagree on which species actually are keystone species. Also, just because an organism is a keystone species in one area doesn’t mean it will be one in another.

Why is keystone species important?

Here’s a random question: What would happen if all of the starfish suddenly disappeared? A likely scenario is that mussels, a favorite food of starfish, would become a lot more common, muscle out all of the other animals that compete with them for food, and dominate the area. Ecologist Robert Paine saw this exact situation happen in one of his experiments and coined the term keystone species in 1969 to describe important plants and animals like the starfish.

A keystone species is a plant or animal that is essentially the glue that holds a specific ecosystem, like a forest or a lake, together. For example, honeybees fly from plant to plant to collect nectar that they eat. Pollen sticks to the bees and spreads to other plants. Without bees, these plants would lack the pollination necessary to make new plants, and many plant-eating animals suddenly would have no food and would either starve or move somewhere else. In this example you can see that the entire area would change quite a lot without honeybees, and that is why the honeybee is often considered a keystone species. Some keystone species are predators, like wolves, which feed on other animals, keeping the numbers of those animals from getting too big. Some keystone species are prey, like rabbits, which are food for other animals but are not in danger of dying out because they breed so quickly and so often.

Keystone species play important roles in the particular environments that depend on them. Without sharks in the ocean or beavers building their dams in streams, these areas would be very different and many animals and plants would die or experience explosive population increases. Though it’s the subject of debate, the term keystone species is important in wildlife conservation. It’s especially used to educate people about how dependent certain ecosystems are on particular keystone species, many of which are declining or in danger.

Did you know ... ?

There is one species of animal that has an especially big effect on many different ecosystems: humans! But are we a keystone species? Robert Paine, who coined the term, said we humans are in our own category. He called humans hyperkeystones due to the fact that human activity has affected—and endangered—so many keystone species.

What are real-life examples of keystone species?

The removal and reintroduction of the gray wolf, a keystone species, has had a major impact on the animal and plant life in Yellowstone National Park. There are many other examples of organisms considered keystone species.


What other words are related to keystone species?

Quiz yourself!

True or False?

Not much would change if a keystone species disappeared or was removed from its ecosystem.