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Daniel_SimberloffEfforts to restore land back to its natural state by reintroducing wild animals have become increasingly popular in recent years.

A study co-authored by Dan Simberloff, a UT researcher, says scientific evidence supporting the potential benefits of this form of restoration is limited at best. The introduction of species into new places is often met with unexpected negative consequences for the environment.

The findings were published today in the Cell Press journal Current Biology.

Simberloff is the Gore Hunger Professor of Environmental Studies in the UT Department of Ecology and Evolutionary Biology.

He partnered with David Nogu├ęs-Bravo, Carsten Rahbek, and Nathan Sanders of the Center for Macroecology, Evolution, and Climate at the University of Copenhagen. Sanders is also an adjunct faculty member in the UT Department of Ecology and Evolutionary Biology.

Rewilding is already occurring, the researchers noted, and cited examples including European bison imported from Poland that now roam Denmark’s Baltic island of Bornholm in places where the animals haven’t lived for thousands of years. In Siberia, scientists are attempting to reconstruct an ecosystem that was lost thousands of years ago along with the woolly mammoth by introducing bison, musk oxen, moose, horses, and reindeer to a place called Pleistocene Park.

The consequences of rewilding are unknown and may potentially lead to local and global extinction of animals, the researchers said. It also might draw already limited funds away from less visible, but more scientifically supported, conservation projects.

Before rewilding is implemented as a major conservation approach, more basic research is needed about the consequences of modifying ecosystems, Simberloff and his colleagues write. They argue that, for now, conservation efforts should focus on protecting biodiversity and reducing major threats to the environment such as deforestation, climate change, and invasive species.

The reintroduction of wolves to Yellowstone National Park is often highlighted as a success story through its cascading effects on the landscape, Simberloff said. But the influence of such reintroductions can be highly variable and hard to predict.

“Only in some cases do you find evidence of strong cascading effects of large mammals, while other examples show only weak effects or even unexpected, but dramatic negative consequences,” he said. “Therefore, we advocate caution and careful consideration both for the animals that are rewilded and the ecosystems they are placed into.”

While hard work, vigilance, and creativity on the part of scientists, conservation practitioners, and policy makers are required to face the world’s sixth mass extinction event, “our hope is that the hard work is grounded in detailed ecological theory and offers clear conservation benefits to all of biodiversity and not just the opportunity to see large, wild beasts roaming the landscape,” the researchers write.

The researchers are now exploring the feasibility, adequacy, and risks of rewilding by studying fossil remains and their DNA in museums around the world. Their goal is to understand changes in ecosystems that occurred in past natural experiments that resemble rewilding.

Simberloff and his colleagues were supported by Det Frie Forskningsrads Forskerkarriere (Danish Council for Independent Research) Program Sapere Aude and the Danish National Research Foundation.



Daniel Simberloff (865-974-0849,

Lola Alapo (865-974-3993,