“Sky islands are mountains in ranges isolated by valleys in which other ecosystems are located. As a result, the mountain ecosystems are isolated from each other, and species can develop in parallel, as on island groups such as the Galápagos Islands.”

So says Wikipedia, and there’s a conservation group dedicated to preserving these evocatively-named habitats (as well as the rather more obscure “desert seas”). But new research suggests that sky islands might not really exist …