Species populations often don’t stay in place. Many move because of climate change, or because the species lives in intrinsically dynamic ‘metapopulations’. One year a species may be thriving in a nature reserve and the next year they may be doing much better somewhere else. So we can’t just choose one place to conserve species. We need to design networks of reserves, so that if one population disappears, it can be recolonised from somewhere else. For example, we’ve mapped populations of butterflies across the UK, including the Marsh Fritillary in Wales, and used population dynamic models to design the best network of nature reserves for these species. We’ve also weighed up the pros and cons of actively moving populations of species that can’t outrun climate change (‘Managed Relocation’).