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Keystone Species and Unintended Consequences

Updated: May 29, 2022

An ecosystem is only as strong as its weakest link. What happens when that weak link is supposed to be its strongest?


On January 4, 2021, the gray wolf was delisted from the Endangered Species Act (ESA). Eight days later, Representative Tom Tiffany (R-WI) introduced the Managing Predators Act (HR 286). This bill would permanently remove the gray wolf in Michigan, Minnesota, Wisconsin, and Wyoming from the ESA. The following month Wisconsin’s wolf hunt exceeded its kill quota by 83 percent in only three days. In May, Idaho passed a law that allows for culling up to 90 percent of its wolf population, while Montana’s legislature made killing wolves easier.


Given how some states are moving to drastically reduce their gray wolf populations, what are the potential implications if this apex species were to become extinct?

What’s an apex species?

An apex species is the top predator in a food chain that plays an essential role in an ecosystem. Animals like polar bears, orcas, and dingoes kill the old and infirm of lower species, keeping their populations healthy and in check. They keep herds moving, minimizing overgrazing and erosion. And they keep smaller carnivores at sustainable levels.


Some apex species are so crucial that they’re considered keystone species.

A defining element for a keystone species is that it is irreplaceable. When it’s removed from an ecosystem, drastic changes between predators and prey quickly follow.

What’s a keystone species?

In the 1960s, the ecologist Robert Paine removed the purple sea star, a top predator, from a coastal tidal patch in the Pacific Northwest. Within weeks the patch’s biodiversity was reduced by half. From this, he coined the term keystone species.

A keystone species “is the glue that holds a habitat together” and “can be any organism, from animals and plants to bacteria and fungi.” A defining element for a keystone species is that it is irreplaceable. When it’s removed from an ecosystem, drastic changes between predators and prey quickly follow.


Keystone species are usually sorted into three broad types:

  • Predators: wolves, hawks, starfish, sealions

  • Mutualists: two or more species that help each other—hummingbirds/plants, bees/flowers

  • Engineers: species that alter ecosystems—elephants toppling trees, birds creating cavity nests, animals digging burrows


Chaos of change

Unable to replace keystone species’ roles, competing species struggle to compensate. Predators jockey for the apex position while prey species adjust to the instability. Amid the chaos of change, no species goes untouched.


This happened in Yellowstone National Park. By the mid-1920s, wolves had been eradicated from the park. Elk herds thrived, resulting in overgrazing and damaged forests. Coyotes became the top gun, while fox and large rodents declined, which led to imbalances with smaller rodents. To restore the balance, park officials began “managing” the elk herds with annual cullings. They did this for the next three decades. This ended in 1995, when gray wolves were reintroduced. The elk herds eventually stabilized while other species adjusted accordingly.

Unintended consequences

As the Yellowstone example shows, the formula for maintaining a healthy ecosystem is intricate and complicated. Every species, large and small, is intertwined in ways that baffle and astound so that when a change takes place, it’s felt throughout the entire ecosystem. That’s why we have to be cautious when altering an ecosystem to achieve a particular outcome. Our efforts might be successful, but they might also bring about unintended consequences.


Further reading

Dunn, Colin. “The Importance of Apex Predators for a Healthy Ecosystem.” Greener Ideal, June 11, 2010.

Keystone Species.” National Geographic, no date.

Role of Keystone Species in an Ecosystem.” National Geographic, September 5, 2019.


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2 comentários


Neanta Parnell
Neanta Parnell
27 de jun. de 2022

This post was so informative. We really need to learn how to coexist with all aspects of our ecosystem.

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Steven Long
Steven Long
02 de jul. de 2022
Respondendo a

Thanks for your comment, Neanta. I agree--we can and should be doing more. Hopefully, by making people more aware, this might spur action.

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