Key species: what they are and examples - Summary and photos

Help the development of the site, sharing the article with friends!

Ecosystems work in a perfect balance from the interactions between organisms. All species are vital to ecosystems, but there is one type of species that, if removed, would create a catastrophic chain reaction: keystone species. In this Green Ecologist article we will explain what are keystone species and what examples are there, in addition to the importance they have.

What are keystone species and what types are there

Key species are organisms that play a important role in population dynamics that, if removed, would have catastrophic effects on the ecosystem with disproportionate consequences in relation to the number they represent. They are characterized by:

  • Have an effect on the abundance of other species.
  • Modify the structure of a community.
  • Exert an up-down effect at lower trophic levels: providing them with essential resources.
  • Prevent the monopoly of dominant species.

Importance of key species

There is the arch analogy to exemplify the importance and how key species influence community structure. In this arch analogy, a corner piece is placed in the center of the arch that provides structure and support, as well as keystone species. If moved, the bow would fall.

The important role that key species play has been exploited by man to recover degraded ecosystems. In these areas, species have been incorporated that were initially eliminated, either for causes such as hunting, climate change or change in land use, among other reasons. As the balance is restored through the reinsertion of key species, the cascade of multiplication of species on which previously pressure was exerted can be unleashed.

Key species can be both large predators and small plants. There are four key species types, which can be classified as:

  • Predators
  • Mutualists
  • Ecosystem Engineers
  • Herbivores

Next, we are going to see examples of key species and some of their characteristics.

Predators or population controllers

This type of key species in the food web is responsible for controlling prey organisms. Predators or population controllers are those who head the food chain. This control results in a cascade effect that affects species in a descending way, even influencing plant communities. If these key species did not exist, herbivorous animals could consume so many vegetables that there could even be a decrease in available oxygen.

Starfish and mussels

The key species concept was coined when Bob Paine discovered that if he removed starfish from a small ecosystem, the mussels would start to over-breed. Fifteen other species from the site disappeared completely due to the movement of mussels. Eliminating any of these other species did not create the same effect. Sea stars they are predators of mussels, and the entire balance of the ecosystem of these waters depends on them.

If you want to know more information about the Starfish: characteristics, reproduction and taxonomy, do not hesitate to read this article that we recommend.

Tiger shark

The Galeo pig Tiger inhabits shallow tropical waters. It is known as the garbage dump of the sea because it can feed on practically everything: from fish, dugongs, turtles, crustaceans and dolphins, to human garbage. Is a top predator, having an important role in the balance of the marine food chain. It can consume injured or recently killed animals, helping to keep the waters clean. By consuming numerous herbivores, they help them not to overconsume plant species or algae, which have an important role in global oxygen production.

Here you can read more about Predators and prey: examples and characteristics.


Mutualism is a type of interaction between species in which both obtain benefits by being associated. In this way, the close relationships that exist between these species can create bridges between the different biological kingdoms. In this other post by Green Ecologist you can read more about Mutualism: definition and examples.

Bees and pollination

Humanity depends on bee populations. This is due to the important pollination work carried out by bees. To feed, they consume the nectar of the flowers and, during the process, help the pollen to be transported so that fertilization occurs. This process is the one that originates both the fruits and the plant development and reproduction. Crops and plants are the basis of our diet, on which the economy, the labor market, industry and ecosystem services also depend. Today they are reducing bee communities due to the excessive use of pesticides and climate change, our food insecurity is getting closer and closer.

Feel free to take a look at this article to find out The Importance of Bees.

Ecosystem Engineers

These are key species that physically modify their environment, as engineers who transform and build. They can be autogenic engineers, where the organism modifies itself, or allogeneic, where they alter materials from the environment with mechanical or physical methods.


This is a kind of autogenic engineer, where its roots protect the coast from waves, wind and water erosion or water. They also provide an ecosystem to house numerous species, such as mollusks or migratory birds. In these other articles you can find more information about what is a mangrove and its characteristics and the types of erosion that exist.

Lianas and tree branches

This type of keystone of an ecosystem is important, as trees spread their branches where birds perch. They may also have flexible extensions as lianas, which are useful for animals to support or move around them.

Ironwood and shadow production

Olneya tesota is a tree from the Sonoran Desert, in Mexico, whose canopy is unique among desert species because it creates a dense pattern with the overlapping branches and leaves. Unlike other trees, the branches do not usually grow close to the trunk, creating a very large refuge area. They are evergreen trees that live up to 800 years, creating a constant microhabitat. Each hectare of ironwood concentrates 100 plant species, and it has been observed that in its presence the plant abundance reaches up to 100%, the height of columnar cacti increases by 87% and the richness of species grows by 60%. .

Beavers and forest maintenance

Beavers cut logs with their sharp teeth to create prey where they collect water to build their habitat, which is also used by several other species. Thanks to this function, forests get rid of weak or old trees to constantly renew themselves. This is a kind of allogeneic engineering.

Parrotfish and sand production

On parrotfish depends most of the sand production. These fish of the family Scaridae They have clustered teeth that form a kind of beak, gnawing at dead corals. After ingesting them, he defecates them in the form of sand. In addition to their important role in soil formation, they help remove wilted corals, allowing new healthy corals to develop.


These key species are involved in plant communities and, in turn, in other organisms that depend on such plants. They have also helped natural selection, where plants have had to develop defense mechanisms, influencing fitness in terms of plant adaptation.

White-tailed deer

The Odocoileus virginianus it feeds on grasses and shrubs, but beyond the effect it exerts directly on this vegetation, it also has indirect effect on numerous animal species. A study[1] did an experiment by erecting fences in the Cuyahoga National Park in the United States to prevent the entrance of the white-tailed deer, while they left other control sites where it could enter. They observed that at the sites where the deer could walk and grazing there was a higher percentage in number of species, compared to the closed site. Animals that indirectly benefit from deer herbivory range from salamanders, snakes, to invertebrates.

Find out more about herbivorous Animals: what they are and examples in this Green Ecologist article.

If you want to read more articles similar to Key species: what they are and examples, we recommend that you enter our Biodiversity category.

  1. Greenwald, K.R., Petit, L.J. and WAITE, T.A. (2008). Indirect Effects of a Keystone Herbivore Elevate Local Animal Diversity. The Journal of Wildlife Management, 72: 1318-1321.
  • Ronzón, R. (2009). Performance of key species indicators to assess disturbances in reef ecosystems Master in Management of Marine Resources Thesis. National Polytechnic Institute. Interdisciplinary Center of Marine Sciences, La Paz, B.C.S., Mexico xii, 153 h.
  • BBC News World. (2022). "Key species": the hope for recovery of degraded ecosystems. Available at:
  • National Geographic. (2022). Keystone species. Available at:
  • Davic, R. (2002) Herbivores as keystone predators. Conservation Ecology (2): r8. Available at
  • Poelman, E., Kessler, A. (2016). Keystone Herbivores and the Evolution of Plant Defenses. Available at:
You will help the development of the site, sharing the page with your friends
This page in other languages: