In the absence of firm evidence, conservationists have been eager to interpret early predator reintroduction studies-largely based on the purported regenerative ecological effects of returning gray wolves ( Canis lupus) to Yellowstone National Park in the mid-1990s-as a rationale for bringing predators back to many parts of the globe. “We only have so many natural experiments,” notes wildlife ecologist Justine Smith of the University of California, Davis. In addition, predator reintroductions such as the ongoing project in Iberá are extremely rare and have lagged greatly behind herbivore rewilding projects, in large part because releasing animals capable of killing people and livestock is so controversial. Part of the problem is, while it’s well accepted that large carnivores play vital ecological roles, just how they shape ecosystems through cascading effects in different environments isn’t well understood. MATÍAS REBAK REWILDING ARGENTINA FOUNDATION “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.
The loss of jaguars ( Panthera onca), pumas (cervu 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.” But seldom do ecologists get to investigate whether those negative effects can be reversed by restoring predators. 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. 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.
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