36 THE SCIENTIST | the-scientist.com

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Can reintroducing apex predators reinvigorate damaged ecosystems?

BY KATARINA ZIMMER

T

he jaguars don’t know it yet, but soon they’ll be free to

roam Argentina’s Iberá wetlands, becoming the first

apex predators to do so in a century. Three adults and

the two-year-olds Amarí and Mbareté currently live in

an enclosure on San Alonso, a patch of high ground in

Iberá’s patchwork of flooded wilderness, lagoons, jungle, and

grasslands. Once a pristine habitat, the region has lost much of

its wildlife since the early 20th century, when ranchers moved

into the area. People killed off native predators to protect live-

stock, and many species were decimated to satisfy a burgeoning

market for fur, leather, and feathers.

Now, wildlife is making a comeback in Iberá, thanks to

an ecological restoration effort spearheaded by the nonprofit

Rewilding Argentina Foundation. Because of the region’s now-

protected status and the reintroduction of locally extirpated spe-

cies to reconstruct ecological communities, the area is thriv-

ing with pampas deer and marsh deer, capybaras, caimans, and

diverse bird and insect life. Yellow anacondas have also been

spotted. By the end of this year, conservationists hope to install

one of the final missing ecological pieces—an apex predator—

with the release of the jaguars.

To Emiliano Donadio, the foundation’s scientific director, the

release not only is crucial to rebuilding Iberá’s ancient ecosystem,

but is a scientific experiment that will provide a rare glimpse of how

the return of one of the world’s largest carnivores could transform

an ecosystem. Scientists know that losing large predators can have

far-reaching, disruptive effects on ecosystems through cascading

forces that reverberate from predators at high trophic levels—the

top of the food web—to their prey and beyond, even sculpting the

abundance and structure of plant life. The loss of jaguars (Panthera

onca), pumas (Felis concolor), and other predators from fragments

of the Venezuelan rainforest after the construction of a hydro-

electric dam, for instance, is thought to be a key factor in triggering

an explosive proliferation of herbivores including monkeys, which

ravaged the vegetation and caused what researchers described as

an “ecological meltdown.”^1 But seldom do ecologists get to inves-

tigate whether those negative effects can be reversed by restoring

predators. “We think that an ecosystem devoid of predators will be

in better shape when the predators come back,” Donadio says, but

that supposition remains largely untested.

Part of the problem is, while it’s well accepted that large

carnivores play vital ecological roles, just how they shape eco-

Rewilding

With Teeth