Immigration's a hot topic - and it applies to non-native plants, animals and insects, all over the world | Tim Blackburn

Biodiversity is great in theory, but there are reasons to fend off invasive alien species and the knock-on effect of their presenceBritain would be a wasteland if it weren't for immigration. Fifteen thousand years ago, most of the country was buried a kilometre deep in ice - not ideal conditions for life. That all changed as we moved out of the last ice age into the current, milder climate phase. The ice sheets retreated, leaving an empty landscape for anything with the wherewithal to seize the opportunity and move in. Tens of thousands of species did, mainly heading north from the European continent to which Britain was then joined. The result was a native biota where almost every species is an immigrant. Our ancestors were among them.Immigration is a natural process, but it's one that has been fundamentally changed thanks to humanity's wanderlust. As we've moved around the world we have taken many other species along with us - some deliberately, some accidentally - to areas they couldn't have reached without our assistance. These include many of the most familiar denizens of the British countryside. Grey squirrel, ring-necked parakeet, horse chestnut, rhododendron - none of these would be in Britain if they hadn't been brought by people. They are what ecologists call aliens. Anywhere people live you'll also find aliens.Tim Blackburn is professor of invasion biology at University College London and author of The Jewel Box: How Moths Illuminate Nature's Hidden Rules Continue reading...