Role of Keystone Species in an Ecosystem

Role of Keystone Species in an Ecosystem

A keystone species helps define an entire ecosystem. Without its keystone species, the ecosystem would be dramatically different or cease to exist altogether.


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Biology, Ecology, Geography

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A keystone species is a life form that affects a whole ecosystem. An ecosystem is a community of plants and animals. A species is a certain group of plant or animal.

No other creature can do the job of a keystone species. Without them, the ecosystem would have to completely change. It could even disappear.

Carnivores, Herbivores, and Mutualists


A keystone species is often a predator or hunter.

In the Greater Yellowstone Ecosystem (GYE), gray wolves are a keystone species. The GYE stretches across the U.S. states of Montana, Wyoming, and Idaho. It has mountains, forests, grasslands, and rivers.

The elk, bison, rabbit, and birds here are food for predators. How they eat and where they live depends on what wolves do.

In the 1800s, hundreds of wolves lived in Yellowstone National Park. The government thought the wolves were damaging the area. They thought the wolves were eating too many elk and bison, and cows on farms. So, by 1924, the government killed all the wolves.

After this, the GYE changed.

There was no top predator. Soon, there were more elk than ever. They ate too much grass and other plants. Plants did not have time to grow back. This hurt the fish, beavers, and songbirds. These animals rely on plants to survive.

More than animals were affected. Stream shores wore away. Plants were no longer there to hold the soil in place. Lake and river temperatures increased. Trees and shrubs no longer covered them in shade.

In the 1990s, the U.S. government began bringing wolves back to Yellowstone. Since then, there are fewer elk. Trees are growing more. Beaver and songbird groups are growing again.


Plant eaters can also be keystone species.

Elephants in the southeast of Africa eat plants. There are many dry grasslands here. Elephants eat the shrubs and small trees. This keeps it a grassland, instead of a forest.

With elephants eating trees, grasses grow easily. Grass feeds antelopes, wildebeests, and zebras. Mice can burrow in the warm, dry soil. Fewer trees make it easier for lions to hunt.

Keystone Mutualists

Animals and plants can work as a team. A change with one would affect the other. It would change the entire ecosystem.

Patagonia is an area in South America. It has huge forests. There, a hummingbird and some native plants work together.

Hummingbirds eat sweet nectar in certain flowers and trees. When they do this, they move pollen. Pollen is a yellow material on plants. When pollen is moved to another part of a plant, it can make seeds. When hummingbirds eat, they move the pollen where it needs to go.

Some of the Patagonian habitats would fall apart without this hummingbird. No other creature can do its job.

Other Organisms Crucial To Ecosystems

Umbrella Species

Umbrella species are like keystone species. The main difference is that umbrella species often travel far. They have larger effects on the different places they move to.

The Siberian tiger is an umbrella species. It travels in an area of more than 998 kilometers (620 miles) in Russia. Deer, boar, and moose in different areas are eaten by the Siberian tiger.

Foundation Species

Foundation species help create or maintain a habitat.

Corals are a foundation species of many islands in the South Pacific Ocean. These tiny animals grow as a colony of sometimes millions of individual corals. The rocky outer layers of these corals create huge walls around islands. These are called coral reefs.

Coral reefs are full of colorful creatures. Tortoises, crabs, sponges, sharks, and fish often live and eat there.

Ecosystem Engineers

Ecosystem engineers also change and maintain habitats.

Some do this by changing themselves. Corals and trees are ecosystem engineers. As they grow, they are a living part of the environment. They are both food and shelter to other creatures.

Other engineers change the environment around them. Beavers are an example. They cut down older trees. This allows young ones to grow. They turn the old trees into dams. Beavers greatly change forests and streams. They make them into wetland areas.

Invasive species are often ecosystem engineers. They are not eaten by larger predators. So, these species move to new environments. They invade or take over. This holds back the growth of native plants and animals. The original animals are still used to the old environment.

Kudzu is an invasive plant. It is a vine in the southeastern United States. Kudzu beats out native species for space and food. It climbs and wraps around other plants. When certain plants disappear, so do some insects and birds. They depend on the original, native plant.

Indicator Species

An indicator species can tell us about changes in the environment. They can send us important messages. They tell us if a habitat is hurting, such as from pollution.

Chesapeake Bay is a body of water in the northeastern U.S. There, oysters are an indicator species. Oysters suck in water. They try to filter it to find little bits of food. Oysters also filter important minerals, soils, and pollutants that enter the bay. If the oysters are not healthy, the bay may not be healthy.

Flagship Species

A flagship species is a symbol for an environmental habitat or problem. A symbol is something that stands for something else.

Flagship species are often loved for how they look. They often appear in movies, TV, or books. Polar bears are a flagship species. They remind us of how the ice they live on is melting because of climate change.

The giant panda is another flagship species. Pandas are a symbol of endangered species. Their species is threatened.

Fast Fact

Keystone HostsPlants and other producers that provide food and shelter for keystone species are sometimes called keystone hosts. Kelp is a keystone host. Kelp forests provide stabilizing shelter for sea otters, and nutrient-rich food for their prey, such as fish and sea urchins.

Fast Fact

Keystone PreyKeystone prey are species that can maintain healthy populations despite being preyed upon. Wildebeests, prey for predators from lions to crocodiles of the African savanna, are an example of keystone prey.

Fast Fact

Keystone TrophicsKeystone species are often predators, but not always apex predators. Instead, they are usually secondary consumers. Sea stars, while voracious predators of mussels and barnacles, for example, are a prey species for sea anemones and fishes.

Fast Fact

Nutrient VectorsKeystone species can sometimes be “nutrient vectors,” transferring nutrients from one habitat to another. Grizzly bears, for instance, prey on salmon. They can deposit salmon carcasses miles from rivers and streams. Salmon carcasses decompose and fertilize the soil with nutrients that may not be available from local terrestrial ecosystems.

Fast Fact

Keystone Paine
Zoologist Robert T. Paine, who coined the term "keystone species," had an unorthodox way of doing his work. Instead of just observing the habitat of the Pisaster ochraceus sea star, Paine experimented by actually changing the habitat. Paine and his students from the University of Washington spent 25 years removing the sea stars from a tidal area on the coast of Tatoosh Island, Washington, in order to see what happened when they were gone. He was one of the first scientists in his field to experiment in nature in this manner.

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Jeannie Evers, Emdash Editing, Emdash Editing
National Geographic Society
Last Updated

October 19, 2023

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