January 3, 2024

A guide to Keystone Species: Definition, examples and why they’re so important

The planet's ecosystems are vast and complex, made up of billions of relationships that rely on each other to survive and thrive. Plants, animals, soil, water, and the climate all contribute to their ecosystem in unique ways, and the loss of any one can have a devastating impact on the rest. 

In ecology (the study of interactions between organisms and their surroundings), there are five broad levels of hierarchy: organism, population, community, ecosystem, and biosphere. Each one depends on the other.

An infographic outlining the five levels of ecological hierarchy
The 5 levels of hierarchy

Understanding these levels is crucial for ecologists to study the complex relationships and processes that occur within ecosystems. Changes to one level can have cascading effects on the entire hierarchy, which emphasizes the interconnected nature of all life on Earth. 

Some species have become ‘key’ to their ecosystem, because of the important role they play in maintaining the health of all levels of the hierarchy.

Keystone species: Nature’s most important allies! 

Keystone species are animals or organisms that play a disproportionately significant impact on their ecosystem, more so than others. Even small numbers of these key organisms are the reason some ecosystems hum with life.

The term was coined by ecologist Robert Paine in the 1960s, who performed a study of starfish along the rocky Pacific coastline. By removing the starfish from an area, the mussel population—the starfish’s primary food source—exploded and overwhelmed the tidal pools, drastically decreasing the biodiversity in the area.  

Starfish in a tidal pool
Starfish control mussel populations to stop them overwhelming tidal areas

When keystone species disappear from their ecosystem, it can lead to cascading effects. Their disappearance can cause dramatic shifts in the community and completely alter ecosystem dynamics. Recognizing and conserving keystone species is vital to the resilience and stability of ecosystems. 

Types of keystone species

Scientists have identified three types of keystone species: predators, ecosystem engineers, and mutualists.

Predators help control the populations of other species, which impacts plants, soils and other animals further along the food chain. Wolves are a great example of this type of keystone species. They tend to prey on sick, wounded or old herbivores (elk, deer, etc) which strengthens the herd in the long run. They also stop the herd from overfeeding. If deer populations are left unchecked, they could excessively eat the grasses and plants other species also rely on to survive. When top predators are lost, it can trigger what’s called a trophic cascade that affects the whole ecological hierarchy. 

A pack of wolves
Wolves are important keystone species all over the world

Ecosystem engineers are creatures that build, destroy or alter habitats. For example, in the Savanna, the size and eating habits of African elephants carve out pathways through dense bush, which makes it easier for smaller animals to traverse the habitat. 

Lastly, mutualists are two or more species in an ecosystem that interact for each other’s benefit. Nothing fits this description better than the honeybee. Bees fly from flower to flower, collecting nectar to take back to the hive. In doing so, the bees spread the plant's pollen far and wide, allowing new flowers to bloom in new areas. 

Keystone species examples

We have already covered a few keystone species, but there are many, many others. Here are a few more examples of nature’s most important species, and the important role they play in their ecosystems. 


Beavers are important ecosystem engineers. Through their dam building, they divert water in rivers to create and maintain wetlands. They also tend to use old or dead trees along riverbanks for their dams, which helps new, healthier trees to grow. The wetlands and rivers create important habitats for a number of plant and animal species. Their engineering skills also help them fight back against natural and man-made disasters, such as wildfire. Here's how:

Prairie Dogs

Found primarily in the North American grasslands, these burrowing squirrel-type animals build complex underground colonies, making them important ecosystem engineers. Their burrows provide shelter for a variety of species, and their eating and foraging habits recycle nutrients back into the soil and keep vegetation from getting out of control.


Not all keystone species are animals! Mangroves are considered keystone because they provide important reinforcement for erosion along riverbanks, and provide essential services for all life in river communities. They provide shelter for small fish and crustaceans to breed and protect their young, filter out nasty invaders from the oceans and can absorb the impact of extreme weather events in tropical parts of the world.


Coral reef
Corals support an abundance of marine life

Corals are widely considered keystone ecosystems. They support an abundance of marine life through their complex structures, and are critical to the survival of a number of fish species. Coral polyps create the foundation of the reef, and only grow a few centimeters each year. They provide protection for many fish and invertebrate species, who use these incredible structures to spawn or hide from predators. Healthy coral means a more stable ecosystem for the creatures that rely on it. Unfortunately, pollution and human interference puts stress on the coral, which leads to what’s known as coral bleaching, and then coral death. This is particularly heartbreaking because it can take decades for reefs to recover once they’re lost.

Sea otters

Sea otters play a key role in maintaining kelp forest ecosystems. Their biggest function is controlling sea urchin populations, which prevents overgrazing on kelp. In the mid-20th century, sea otters in the Pacific Northwest were severely hunted for fur and meat. As a result, sea urchin populations exploded, leading to the deaths of kelp forests along the coast. The decline of kelp had cascading effects on the local biodiversity.


A vulture against a black background
Vultures are the planet's clean-up crew

Considered nature’s sanitation crew, vultures are scavengers that play an important role in preventing the spread of disease by quickly feeding on dead and rotting carcasses. Vultures live on every continent (except Antarctica and Australia). Their presence helps keep other scavenger populations under control, such as feral dogs in urban areas. Vultures also protect us. A recent study showed that between 2000 and 2005, human death rates rose by more than 4% in vulture-suitable areas of India after the birds nearly went extinct. There was also an increase in poor water sanitation and reported rabies cases. 


Another important ecosystem engineer, oysters create complex reef-like structures that filter water and improve its overall quality. In fact, a single oyster can filter up to 50 gallons of water a day! Their hard shells and abundance in marine areas create safe havens and habitats for all kinds of marine life. They have also been an ancient food source for humans, and considered a delicacy. As a result, oyster populations have declined, and with them the abundance of jellyfish, eels, crabs, sea anemone, and other species used the oyster reef as a source of habitat and food.

Leafcutter Ants

Close-up of an ant
Ants are tiny, but their vast numbers mean they can influence entire habitats

Despite being very tiny, Leafcutter ants are ecosystem engineers in tropical forest biomes. Their main function is to harvest and process leaves to feed and maintain enormous underground fungal gardens. The fungi that grow as a result of their labor is the ants primary food source, which means they are also mutualists. They also add hundreds of thousands of kilograms of leaf litter to the forest floor every year, keeping the soil nutrient rich and fueling the forest.

At Planet Wild, we talk a lot about keystone species. Many of our missions involve protecting these crucial species from extinction and harm. Whether it’s creating new habitats for Little owls in Germany or combatting Elephant-Human conflict in Tanzania, we are committed to protecting our planet’s most vulnerable keystone species from an uncertain future. 

About Planet Wild

Planet Wild is committed to rewilding the planet through monthly missions that work directly with grassroots organizations dedicated to fighting the biodiversity crisis. When you become a Planet Wild member, your contribution will directly fund innovative and exciting projects all over the world, so you can make a difference from home. Learn more about what we do here.

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