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Amazing Wildlife Ecology

What is a keystone species? Definition and four examples!

A keystone species is an organism that plays an exceptionally large role in its ecosystem. It provides materials or services that enrich the lives of other organisms in the ecosystem. Without the keystone species, the ecosystem would look very different and other organisms that rely on the keystone species would suffer. Now, let’s look at a few examples of keystone species!

Beavers in Wetlands

A common example of a keystone species is a beaver in a wetland. Beavers build dams on streams, causing water to back up and form ponds and wetlands. The result is a much more complex ecosystem with a greater variety of habitats.

A beaver wetland can support a very diverse plant and animal community. Beaver ponds provide a place for other animals to live and forage. A beaver wetland is a great habitat for wetland plants that like to grow in standing water. Without the beaver, the wetland ecosystem slowly degrades.

Saguaro Cactus in the Sonoran Desert

close up photo of prickly cactus plant

Like the beaver, the saguaro cactus is a keystone species. In the Sonoran Desert ecosystem, the saguaro plays a central role providing shelter and food for many other species.

Birds like elf owls, hawks, and woodpeckers live in cavities within the saguaro’s trunk. The saguaro’s flesh helps keep these homes temperature regulated so their occupants stay cool during hot desert days.

The saguaro flower provides nectar that feeds desert pollinators, like bats, doves, and bees. Once pollinated, the saguaro makes large fruits that are also a vital food source for desert animals. Coyotes, tortoises, birds, and others eat the fruit and disperse the saguaro’s seeds in their scat.

Many desert animals have a type of symbiotic relationship with saguaros known as mutualism. This means both the animal and the saguaro benefit from the relationship.

If you are studying keystone species in your classroom, I highly recommend checking out my Saguaro Cactus learning materials, and my Desert Ecology Unit!

Prairie Dogs in Grasslands

Prairie dogs are keystone species in grasslands and prairies because of their tunnels. They are exceptional excavators that build large networks of underground tunnels. These tunnels actually help keep the soil healthy. Digging tills and aerates the soil, and prairie dog scat provides a fertilizer for prairie plants.

Additionally, when prairie dogs abandon burrows, other prairie animal species can move in and use these homes. Not all animals are as good at digging as prairie dogs, so they rely on abandoned prairie dog homes for shelter. Finally, prairie dogs are a food source for grassland predators like coyotes and hawks.

Wolves in Forests

Although scarce today, wolves are a natural keystone species in many types of forests. Wolves help keep the populations of deer, elk, and other undulates under control through hunting them. Amazingly, this impacts the plant community of the forest! Let me explain: deer and elk are voracious plant eaters. When deer and elk numbers grow unnaturally high, plants struggle to grow fast enough to keep up with the hungry undulates. But when wolves are around, the deer and elk populations stay in check, and the plants benefit.

Even a few wolves can really make an impact. These is because the presence of wolves changes the behaviors of deer and elk, scaring them into more protected parts of a habitat. When there are no wolves around, deer and elk will more freely browse in any part of the habitat, including open areas like meadows and riparian zones.

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References and Further Reading

  1. Donegan, C. (2021). Leave It to Beavers: Keystone Species Provides Nature-based Restoration. Maryland Department of Natural Resources. Available: https://news.maryland.gov/dnr/2021/01/01/leave-it-to-beavers-keystone-species-provides-nature-based-restoration/
  2. Fortin, D., Beyer, H. L., Boyce, M. S., Smith, D. W., Duchesne, T., & Mao, J. S. (2005). Wolves influence elk movements: behavior shapes a trophic cascade in Yellowstone National Park. Ecology86(5), 1320-1330.
  3. Kotliar, N. B., Baker, B. W., Whicker, A. D., & Plumb, G. (1999). A critical review of assumptions about the prairie dog as a keystone species. Environmental management24, 177-192.
  4. McDonald C. (n.d.). Saguaro (Carnegiea gigantea). Plant of the Week. U.S. Forest Service. Available: https://www.fs.usda.gov/wildflowers/plant-of-the-week/carnegiea_gigantea.shtml
  5. National Park Service (n.d.). Prairie Dogs: Pipsqueaks of the Prairie. Badlands National Park. Available: https://www.nps.gov/articles/prairie-dogs.htm
  6. Ripple, W. J., & Beschta, R. L. (2004). Wolves and the ecology of fear: can predation risk structure ecosystems?. BioScience54(8), 755-766.

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