After wolves were reintroduced to Yellowstone national park in 1995, researchers noticed some big ecological changes, leading to the regeneration of the landscape. It’s an argument used to justify the return of apex predators – but it’s increasingly being challenged. Phoebe Weston talks to Ian Sample about whether wolves really have the power to shape ecosystems, and what that means for the debate about bringing them back to the UK. Help support our independent journalism at theguardian.com/sciencepod