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What Happens When Predators Disappear

It's Predator Week here at the blog. What's your favorite predator, either existing or extinct?

The loss of wolves in the American West set off a cascade of changes to the region's food web. Courtesy of Flickr user WSK_2005.

Eliminating predators from an area may be seen as a good thing; you’ve gotten rid of the animal that has been killing off your livestock or even your neighbors. Others often see the loss of these species with a somewhat sad, romantic eye; how awful to never again see such a creature. But the reality of the loss of predators is far worse, say ecologists reporting in Science, and “may be humankind’s most pervasive influence on nature,” they write.

Part of that is because the worst extent of such a disappearance—extinction—is irreversible, unlike other environmental impacts, such as climate change. But it’s more because the loss, or even reduction in numbers, of predators in an ecosystem can set off something caused a “trophic cascade” in which the change in predator population has effects across the food web and ecosystem. For example, when wolves were eliminated from the American West, there were changes in the elk population and the vegetation the elk ate.

“Trophic cascades have now been documented in all of the world’s major biomes—from the poles to the tropics and in terrestrial, freshwater and marine systems,” the scientists write.

But changes to the food web aren’t the primary problem for human populations; the effects on ecosystem processes are often more dangerous. And many of these processes are big enough that even people in industrialized nations cannot protect themselves. The changes in vegetation that occur when the herbivore population is allowed to rise unchecked can change the frequency and intensity of wildfires. Infectious diseases can become more common; for example, in some parts of Africa where lions and leopards have become scare, populations of olive baboons have changed their behavior patterns, increasing their contacts with the humans nearby. Intestinal parasites have become more common in both the baboons and the people.

Then there are changes to soil bacteria, water availability, biodiversity and a host of other ecosystem features that we depend on to grow our food, keep our environment habitable and stay healthy. The scientists conclude:

We propose that many of the ecological surprises that have confronted society over the past centuries—pandemics, population collapses of species we value and eruptions of those we do not, major shifts in ecosystem states, and losses of diverse ecosystem services—were caused or facilitated by altered top-down forcing regimes associated with the loss of native apex consumers or the introduction of exotics. Our repeated failure to predict and moderate these events result not only from the complexity of nature but from fundamental misunderstandings of their root causes.

We can’t predict what will happen when a predator is lost from an ecosystem; there are too many unknown ways that species interact and the processes take place over scales of tens to thousands of square kilometers. The true effect of a loss can’t be known until years or decades after it has taken place. It’s another reason to save these incredible creatures—for our futures.

With this reminder of the importance of predators, we’ve decided to hold Predator Week here at the blog. What’s your favorite predator, either existing or extinct? Which ones would you be sad to lose forever?

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About Sarah Zielinski
Sarah Zielinski

Sarah Zielinski is an award-winning science writer and editor. She is a contributing writer in science for Smithsonian.com and blogs at Wild Things, which appears on Science News.

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