Eradication of Small Mammals Is Harming Vital Ecosystems

In an effort to protect grasslands, a plan to cull pikas and zokors in China is having the opposite effect, say scientists.

We've seen it time and time again. When you remove a keystone species from an ecosystem, things fall apart. Keystone species play a critical role in maintaining the structure of an ecological community, and removing them has consequences. Oftentimes, government-mandated culling programs try to address what might be a problem for some (say, cattle ranchers), only to find that the ecosystem quickly degrades when you take out a key player. Think wolves in Yellowstone or beavers in the American West.

Now, a new paper reveals another example of the eradication of a keystone species gone wrong. Published in the Journal of Animal Ecology, the authors suggest that eradication measures to protect grasslands in China's Qinghai-Tibetan Plateau are harming the ecosystem and should be stopped.

The eradication policy was introduced in 2000 and calls for the culling of two mountain-dwelling herbivores, the plateau pika and the zokor. The two keystone species are ecosystem engineers because of their modification of and impact on the environment.

What is a Trophic Cascade?

A related concept to keystone species, a trophic cascade is an ecological event that involves changes to the structure of an ecosystem resulting from changes to animals or plants at one or more levels of the food chain.

The authors say that the extermination program was not based on studies that considered the full effects of eradicating these burrowing mammals.

"The government agency's policy of conducting large-scale animal culling campaigns each year is not a good approach," says Professor Johannes Knops from the Health and Environmental Sciences department at Xi'an Jiaotong-Liverpool University, and a corresponding author of the study.

Knops and the study's first author, Dr. Wenjin Li from the College of Ecology at Lanzhou University, propose replacing the eradication policy with a nature-based control strategy.

"Our research shows that using natural predators and other ecological factors to regulate burrowing mammal populations can be a more sustainable and effective approach to grassland management."

Global Implications

The study notes that burrowing mammal populations have been "drastically reduced by extensive extermination programs in grasslands worldwide."

In the United States, we see this with another keystone species; our prairie dog populations. As the Humane Society of the United States explains: "Human-caused changes to the grasslands stemming from crop agriculture, livestock grazing, energy development, residential and commercial development, prairie dog shooting, poisoning campaigns and plague (an introduced disease) have caused the five species of prairie dogs to disappear from an estimated 87-99% of their historic (1800s) range, depending on the species.

Yet, burrowing mammals do amazing work for the ecosystems they inhabit.

Among other ecosystem services they provide, they increase plant diversity, seed dispersion, and light availability, while their burrows serve as habitat and refuge that improves the abundance of birds, amphibians, reptiles, insects, and spiders. And so much more...

As the study authors note, their research has important implications for grassland management practices globally.

China's eradication policy is part of a nationwide initiative called the Returning Grazing Land to Grassland project. The idea behind it is that the rodents cause damage to grasslands by competing with grazing livestock for food, which, they believe, causes soil erosion.

Yet the new study explains this isn't the case.

Knops says: "If we look at the grasslands, we will find numerous plant species, and not all animals eat the same plants, so it is crucial to consider the entire food chain rather than killing all the small mammals."

The researchers advise that the eradication policy needs to be reconsidered and revoked, as small burrowing mammals play crucial ecological roles in grassland management.

Poison and Conflict

The authors also look at the poisoning method being used to eradicate the animals and note its adverse effects. (As if removing keystone species wasn't bad enough, they are also flooding the grasslands with poison. What could possibly go wrong?)

The authors discuss the unintended consequences of the poisoning method, including the development of resistance to poisons by target species and potential harm to non-target species.

The eradication of these keystone species can also add to human-wildlife conflict by reducing natural predator populations.

Knops says, "It's important to consider the knock-on effects of reducing the small burrowing mammal population. If there are fewer small mammals, there is less food for their natural predators, such as red foxes, steppe polecats, upland buzzards, brown bears and mountain weasels."

"Not only will these larger mammals start to look for alternative food sources and increasingly prey on livestock, causing more human-wildlife conflict," Knops adds, "but their populations will also decrease."

"The eradication policy, therefore, causes the opposite effect to the one intended, as when the number of the pika and zokor's natural predators is reduced, burrowing mammal populations can increase rapidly. This then requires more human control, which is costly and negatively impacts non-target species and the environment."

A Better Approach

That said, the authors argue that while burrowing mammal populations should not be totally eradicated, they can be controlled with a nature-based strategy that uses natural predators and other environmental factors. An approach like this works in harmony with the environment, not against it.

They suggest the use of nesting spaces for raptors and reducing the over-grazing of livestock on the grasslands. "This allows the grass to grow and keeps the small mammal population at a manageable level, as they prefer shorter vegetation."

"By maintaining a stable, low density of burrowing mammals using natural predators and ecological factors, we can promote sustainable livestock grazing practices while also preserving biodiversity and reducing human-wildlife conflicts," says Knops.

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