Predators and Plants

Predators and Plants Photo Credit: Clipart.com

Eliminating bears, wolves, and other top predators has far-reaching consequences.


How predators protect plants. I’m Bob Hirshon and this is Science Update.

(Wolf howl)

The howl of the wolf isn’t heard as much as it used to be, and as a result, prey like moose, deer, and elk are thriving. But according to Oregon State University forestry professor William Ripple, this isn’t a good thing. He analyzed 42 ecological studies over the past 50 years. And he found that declines in top predators, especially wolves, lead to a significant loss of plants and trees—because there are more large herbivores like deer to eat them. And he says we probably can’t do the wolves’ work by hunting the herbivores ourselves.

For example, the wolves are on the ground 24/7, and behaviorally they're very different than human hunters.

But reintroducing wolves to an area, as was done in Yellowstone National Park, has been shown to restore many trees and plants to healthier numbers. I’m Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

Every ecosystem maintains a delicate balance of predator and prey organisms. There have been many studies showing that harming one player in the ecosystem's food web can cause a chain reaction of consequences for other animals and plants. So in that sense, this study is just one more example of that.

However, this study has a few distinctive features. First, it's actually an analysis of dozens of other studies, going back fifty years. Second, it shows a clear relationship between the loss of one type of animal—top predators like bears and wolves—and organisms that are affected indirectly by that loss, namely plants and trees.

Predators, like wolves, bears, lions, and sharks, may be the dominant players in their own ecosystem, but humans have not been particularly kind to them. Perceived as killers themselves, top predators have often become targets for hunting. In fact, for many decades, wolf hunting was explicitly encouraged by the U.S. government, and wolf populations plummeted from hundreds of thousands to a few hundred by the mid-20th century. 

While eradicating predators like wolves has short-term benefits to their prey, who presumably would rather not be eaten, the long-term effects can be harmful to the entire ecosystem, including prey animals. Ripple's analysis shows that wherever wolf populations decrease, plant diversity decreases as well, because there are more herbivores like deer to eat the plants. Over time, the loss of plants deprives many other creatures of food and shelter, including the deer themselves. Since plants soak up greenhouse gases like carbon dioxide from the atmosphere, the plant loss also contributes to climate change.

Some people might ask why we don't just hunt the deer and moose to decrease their numbers. But as Ripple explains, human hunting probably can't control herbivore populations like wolves, their natural predators. It's also significant that programs to reintroduce wolves to certain areas, like Yellowstone National Park, have proven successful, and in those places, the diversity and quantity of plants and trees has actually increased over the years. All this goes to show that taking any piece out of an ecosystem can leave an unexpectedly big hole.

Now try and answer these questions:

  1. What is the relationship between top predators, like wolves and bears, and plants?
  2. What are some of the consequences of plant loss?
  3. What are some of the consequences of the loss of top predators?
  4. This study analyzed dozens of other studies to draw general conclusions. Why do you think this is useful?
You may want to check out these related podcasts:

Sardines tells how a tiny fish on the other end of the food chain could help save countless other creatures.

Everglade Pythons delves into the damage caused by introducing non-native predators to an ecosystem.

Going Further

For Educators

The Science Update lesson Sardines tells how a tiny fish on the other end of the food chain could help save countless other creatures.

Everglades Pythons delves into the damage caused by introducing non-native predators to an ecosystem.

The lesson Tigerland and Other Unitended Desitinations provides an introduction to conservation biology via the memoirs of a scientist who has traveled throughout the world to study and defend endangered species.

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