Keystone species; what they are, and some examples of keystone species

When we are talking about conservation of species, we often hear about keystone species. In this post, I want to write about what exactly keystone species are, and why they are important.

How we define a keystone species

Many people are under the impression that a keystone species is any species of organism that have a really big impact on the habitat it is living in. This is almost correct, but the species need to meet another criteria in order to be a keystone species. To distinguish between an important species and a keystone species, we must know that the keystone species must provide the environment with a disproportionately large effect compared to its numbers. This means that the biomass (total weight of the entire species or population) must be a lot lower than the service it provides to the ecosystem. In other words, it must have a much larger effect than we originally anticipate by its numbers.

Some examples of keystone species, and why they are considered keystone species

Let us start by a pretty common example, such as the grey wolf (Canis lupus). This is an apex predator that feed on large herbivores such as moose, deer and roe deer, and are in many parts of the world important to keep these herbivore populations from growing too high. If we were to remove all of the wolves, the population of (for example) deer could rapidly grow so large that it would graze down most of the available food in the area. This increased population could then lead to new individuals not getting enough food, and starve to death.

Canis lupus. Image by Juan José González Vega, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.

A worst case scenario if all wolves were wiped from a certain ecosystem would be that new trees and plants were grazed down, so the plant biomass would over time be a lot smaller, while the herbivores would be filled with density-dependent diseases, all while competing for a limited amount of food. Over time, the entire ecosystem would look a lot different from what it does with the wolves around. Of course, in this scenario another predator could replace the wolf, making the environment be less affected by the removal of wolves, which is actually what a lot of places are doing these days; replacing wolves by increasing human hunting on the herbivores.

Another great example of a keystone species in the beavers (Castor canadensis and C. fiber). As most people are already aware of, they create dams. These dams can severely affect an entire ecosystem by flooding an area that was previously not flooded, changing it by a lot. This would lead to a big change in the community of insects and other small animals, which would be likely to attract more birds to the area. These birds might then attract predators, and after some time, the entire ecosystem has been changed, with many new species of both insects, birds, fish and other animals. If you remove the beavers from the ecosystem, the dam will eventually break, and there will be massive damage to the whole community of species living there. Species such as the beaver are known as ecosystem engineers, which are species that alters the entire ecosystem by their presence.

A beaver dam, which helps flood areas and create new types of ecosystems. Image by Cheryl Reynolds, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.

For my third example of a keystone species, I am going to link you to a previous post I wrote about kelp forests. In that post, I wrote about how sea otters (Enhydra lutris) are responsible for keeping these kelp forests healthy, and a reduction in the sea otter population lead to the kelp forests disappearing! This is a very good example of a keystone species, because we don’t really expect the sea otters to affect something as big as the kelp forests, but they really do. If you are interested in learning more about this, check out the post I linked to.

All of these examples are true keystone species because the total numbers of both wolves, beavers and sea otters are pretty low compared to how much they affect the ecosystem. A single pack of wolves could easily be responsible to keeping balance to an extremely large area, and a single family of beavers could flood several square kilometers of forest to create a new ecosystem. So even a few individuals can entirely change the ecosystem, making them great examples of keystones species.

Thanks for reading

Thanks for reading my post about what a keystone species is. I hope that you by now realize that they are very important to keep certain ecosystems alive and healthy, and know the difference between a keystone species and a species that is important to the community by being a big portion of the biomass. And as always, don't be afraid to leave questions and comments in the comment field below!

About the author

Hi, I’m @valth! I live in Norway with my girlfriend, our newborn son, and our two dogs, one of which is seen wearing a bow tie in the profile picture!

I am very passionate about nature and biology, and have been studying ecology for a few years now. My passions are mostly within conservation biology, mycology (the studies of mushrooms), animal behavior and general microbiology. I really enjoy both the theoretical aspect, as well as the more practical aspect of biology, and I spend about as much time in front of biology textbooks as I do spend on finding and identifying plant, mushroom and animal species in the forests.

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