Large predators are vanishing worldwide due to their vulnerability to habitat loss, emerging diseases and persecution. Predators protect biodiversity, and their loss has been attributed to changes in vegetation communities and the decline and even extinction of small wildlife.
Measuring the effects that big predators have on ecosystems is difficult because they live at large scales. “Natural experiments” – where environmental change occurs in the wild – offer an opportunity to observe large-scale ecosystem change and investigate the influence of large predators on ecosystems.
The unprecedented decline of the Tasmanian devil from a novel transmissible cancer is providing one such rare natural experiment. Spread by the transfer of live tumour cells when devils bite each other, Tasmanian devil facial tumour disease (DFTD) has spread from its origin in the north-east of Tasmania in the mid-1990s to most of the island state. Devil populations suffer immediate and dramatic local decline, to more than 90%, after 6 years. It’s expected that wild devil populations will remain suppressed for decades, although evolution of the devil and the tumour is expected to lead eventually to an endemic disease and devil recovery.
Apart from the 20th century extinction of the thylacine, Tasmania retains an almost intact community of mammals, and mammalian and avian...
