Above: The snowshoe hare is a prey keystone species in the boreal ecosystem (D. Gordon E. Robertson, Wikimedia Commons)

The world is full of habitats where plants and animals interact with the physical environment around them. These areas are called ecosystems. Often, certain organisms will have a bigger impact on an ecosystem than others. They can also help maintain the ecosystem.

These organisms are called keystone species. There are many types of keystone species. Each type has a different role to play in their ecosystem. The main types of keystone species are predators, prey, plants, and ecosystem engineers.


A predator keystone species plays a large role in regulating the population of the animals that they kill and eat. Predator keystone species feed on species that would otherwise use up a lot of the ecosystem’s resources. And when resources are scarce, other species struggle to survive.

A good example of a predator keystone species is the sea otter in the North Pacific Ocean. It feeds on sea urchins. Sea urchins eat kelp (seaweed), which is also a food source for many other organisms in the ecosystem. If there were too many sea urchins, these other organisms would run out of food.

So the sea otters help maintain the ecosystem by keeping the sea urchin population down. They help make sure there is enough kelp for the rest of the wildlife to feed on.

Did you know? The disappearance of keystone species can lead to the arrival of new plants and animals that push out the native species in the ecosystem. This causes a decline in the native populations.


A prey keystone species is an important food source for organisms in the ecosystem. If a prey keystone species disappeared, it would cause a food shortage in the ecosystem. Other species could go extinct or have to travel elsewhere to find food. And this would mean a big change for the ecosystem.

A good example of a prey keystone species is the snowshoe hare in Canada’s boreal forests. This large population is a food source for many different species in the ecosystem, including the Canada lynx. The loss of the snowshoe hare would significantly change the boreal forest. In particular, it would cause a major decline in carnivore populations.


A plant keystone species provides food or shelter for important herbivores and pollinators. The loss of these plant species could lead to a population decrease in various organisms that depend on them.

An example of a plant keystone species is the sugar maple. Found in central and eastern North America, this tree the main source for maple syrup. But it is also important because its root system brings water up from deeper in the ground. This helps other plants in the ecosystem.

Sugar maples also provide homes for many insects and birds. Mammals such as deer and squirrels feed on sugar maple bark and seeds. And the leaves that fall from the trees each fall provide shelter and food for other animals, such as earthworms.

Did you know? Just like keystone species, pathogens can sometimes have a huge impact on an ecosystem. For example, the distemper virus killed many African lions in 1994, which impacted the animal populations that the lions preyed on.

Ecosystem engineer

The sugar maple is also an example of an ecosystem engineer. These species create or change habitats in ways that have a big effect on nutrient cycling. The nutrient cycle is how nutrients move through the environment and in and out of organisms.

Ivory tree coral is another ecosystem engineer. It lives in the Caribbean Sea, in the Gulf of Mexico and off the coast of Florida. By providing food and shelter to other organisms, ivory tree coral helps these other organisms survive. In fact, this keystone species is home to over 300 invertebrate species, including fish such as snapper and sea bass.

Did you know? Coral is actually an animal species. It’s often mistaken for a plant because when it sits on the ocean floor and appears rooted, just like a plant.

A classic example of an ecosystem engineer that you may have seen with your own eyes is the beaver. Beavers build dams. These dams significantly alter the exchange of nutrients through the ecosystem, which can impact the growth of animals and plants. For instance, beaver dams can create habitats for birds. Without the dams, the birds would have trouble surviving in the ecosystems.

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As you can see, keystone species play important roles in many ecosystems around the world. Scientists are continually finding more and more new keystone species. Many species depend on their ecosystems for survival. With the help of their keystone species, these ecosystems can function and flourish for many years to come.

This article was updated by Let's Talk Science staff on 2017-05-25 to reflect the fact that coral is an animal species and to add the example of the sugar maple.

Learn More!

About keystone species:

Keystone species (2011)
K. Rutledge et al., National Geographic Encyclopedia

Keystone species (2010)
S. Wagner, Nature Education Knowledge Project

About scientific research on keystone species:

Influence of beaver dam density on riparian areas and riparian birds in shrubsteppe of Wyoming (2008)
H.A. Cooke & S. Zack, Western North American Naturalist 68

Functionally dominant herbivores as keystone species (2002)
J. Higdon, Ecology and Society 6

Killer whale predation on sea otters linking oceanic and nearshore ecosystems (1998)
J.A. Estes, M.T. Tinker, T.M. Williams & D.F. Doak, Science 282.
Link to abstract. Registration or subscription required to view full text

Adrian Kuchtaruk

Originally from Sudbury, ON, currently pursuing an undergraduate at Queen's University. I have actively tutored many of my peers and other students in subjects ranging from chemistry, biology and physics, to calculus and functions. I have a strong interest in evolutionary biology and am looking to further my studies by pursuing a masters degree in the near future. I have been an active volunteer with Let's Talk Science and am looking to further my love of science by volunteering with Curiocity. In my spare time I love to play basketball and going out on the lake during the summer.

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