What Are Keystone Species? - Definition & Examples

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Lesson Transcript
Linda Fye
Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

Understand the definition and importance of a keystone species in an ecosystem. Read about some examples of keystone species that show how necessary they are for a healthy environment.

Definition of a Keystone Species

Before the 1800s, as many as 60 million American bison roamed the Great Plains. As European settlers arrived, bison were increasingly slaughtered until their numbers reached the thousands. The loss of the bison was devastating to the Great Plains ecosystem. Bison would graze as they migrated and ate only certain types of grasses. They would also trample and roll around in the dirt creating holes that could hold water. Both of these behaviors made the Great Plains very diverse in both plant and animal species, and this kept the ecosystem healthy. The bison's important role in keeping the Great Plains healthy makes them what is known as a keystone species. Fortunately, the bison population has recovered quite a bit, so they can continue their role as a keystone species in some places.

A keystone species is a species that plays a particularly important role in an ecosystem. In order to understand that role, you need to understand what an ecosystem is. An ecosystem is all organisms living in a certain area and the environment surrounding that area. As an example, consider your neighborhood. You, all the other people that live there, the birds and bugs, and all of the plants interacting together would be like an ecosystem. In an ecosystem, a keystone species' importance is out of proportion to the number of species. It was once thought that only the top predators in an ecosystem could be keystone species. A top predator would be like a bear in a forest ecosystem or a lion in an African grassland ecosystem. It is now known that all different types of species can be considered keystone. Anything from plants to microorganisms can have the important role of keystone species in different ecosystems.

Examples of Keystone Species

One example of a keystone species is the prairie dog. They dig tunnels that form prairie dog towns, which can be hundreds of acres in size. The towns help the prairie by providing homes for animals like black-footed ferrets, burrowing owls, and snakes. These animals become food sources for coyotes, birds, and badgers. Also, as the prairie dogs dig tunnels, it churns the soil making it healthier and better for plant growth and insect habitat. The prairie dogs allow better diversity in the prairie, and the prairie would change or die without them.

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Additional Activities

Keystone Species Research

In this research activity, students will find a keystone species that was not described in the lesson and research its role in the ecosystem, its importance, and current threats. Prior to starting the assignment, students should review quality sources that are appropriate for the assignment, such as World Wildlife Foundation (WWF), National Geographic, as well as sources written by scientists, universities or news outlets.

For example, a student might choose to research the orangutan. The student would describe where orangutans live, what they eat and how they look. They would then describe the reasons it is a keystone species, such as its importance in seed distribution in the forest. The student would then explain why it is important for other species in the ecosystem, and current threats, such as deforestation due to the palm oil industry.

Student Instructions

In this research activity, you'll be learning about one of many keystone species. First, research different keystone species in an ecosystem you are interested in, such as the desert or the ocean. Then, choose one that is not described in the reading to search, such as orangutans, elephants, or sea stars. You will research details about why it is a keystone species, its role in the ecosystem, the importance of it to the ecosystem and the current threats. Once you have your research you will create a final product in the form of a power point, essay or a poster. To make sure your product meets the requirements, look at the criteria below.

Criteria For Success

  • One keystone species is researched
  • Background of the keystone species' is explained, including how it looks, where it lives and what it eats
  • Species' role in the ecosystem is described
  • Species' importance to the ecosystem is described
  • Threats to the species is discussed and possible solutions

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