Trophic rewilding: impact on ecosystems under global change

Human-induced global change is increasingly affecting life on our planet, including living conditions for humans themselves as well as the resources we depend on 1,2. As a result, species diversity is strongly declining 3–5. The Living Planet Index shows a 58% global decline in populations of amphibians, fish, reptiles, mammals and birds between 1970 and 2012, varying from 36 to 38% in terrestrial and marine ecosystems to 81% in freshwater habitat 6. Habitat loss or degradation and overexploitation are the main causes of these steep declines. Since the worldwide expansion of modern humans (Homo sapiens) began, humans have overexploited vertebrates, with a bias to the largest animals being extirpated first, from the Late Pleistocene extinctions of terrestrial megafauna to the ongoing declines of terrestrial, marine and freshwater large-bodied animals 7–11. There is increasing evidence that this global wildlife loss, or defaunation, does not only imply the loss of charismatic animals but also the functions they have in ecosystems 12–16. To restore these missing functions, a novel ecological restoration technique has emerged, referred to as rewilding 17. Rewilding aims to restore natural processes in ecosystems in general, and often focuses on re-introduction of missing large wildlife species or, in case these went extinct, their proxies 18. Rewilding is increasingly implemented in practice globally, with a strong emphasis on Europe and the re-introduction of large herbivores 19,20.