Prehistoric-restoration schemes such as those described in your News Feature (Nature 462, 30–32; 2009) are highly unusual. Introducing a mix of native and exotic ungulates into former agricultural land could constitute a risky conservation strategy.
Reintroduction of native species to portions of their former range from which they were extirpated is a well-established conservation tool. But there are no scientific grounds for introducing animals such as elephants, camels, cheetahs and lions into novel environments. Numerous scientifically driven concerns bear on these maverick programmes, including adverse effects of alien species on the ecosystems they are meant to foster; importation of diseases that may leap to native species; escapes that lead to hybridization; and predators jumping fences to endanger livestock.
There are sociopolitical concerns too, such as plundering wildlife from countries and ecosystems where they are naturally found in order to stock game parks, and persuading a conservation-weary public to accept large charismatic exotics as substitutes for contemporary native species and ecosystems.
We therefore advocate a moratorium on importing non- indigenous megafauna into ecosystems. Ill-considered, poorly documented introductions cannot be trusted to turn back the ecological and evolutionary clocks on anthropogenic change.
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Caro, T., Sherman, P. Rewilding can cause rather than solve ecological problems. Nature 462, 985 (2009). https://doi.org/10.1038/462985b