The world’s first global analysis of the distribution of established alien species has revealed the “hotspots” where aliens are taking hold.

Alas, we are not talking about “I want to believe” aliens of the little green men variety, but invasive species that have rocked up somewhere that isn’t their natural habitat, looked around and said “Hey, I like it here, I think I’ll stay a while,” usually to the detriment of the flora and fauna already there.  

The international team of researchers revealed that islands and mainland coastal regions are the world’s hotspots for invasive plant and animal species, with the top three being the Hawaiian Islands, New Zealand’s North Island, and Indonesia’s Lesser Sunda Islands.

The researchers hope their findings, published in the journal Nature Ecology and Evolution, show that more effective measures need to put in place to stop further invasions into delicate ecosystems that can’t cope.

"We need to be much better at trying to prevent the introduction of species that can be harmful in the first place," said team leader Dr Wayne Dawson of Durham University, UK, in a statement. "Prevention is better than cure with invasive species."

The researchers studied existing data and created a database with eight categories, including ants, amphibians, birds, mammals, freshwater fish, reptiles, spiders, and vascular plants, and studied their distribution across the world.

This led them to establish that islands and coasts had higher numbers, so they focused on studying 186 islands and 423 mainland regions. They found that Hawaii had the most alien invaders, with high numbers of invasive species in all eight categories found there.

Staggeringly, half of all New Zealand’s plants were not native, while its battle with invasive mammals – especially possums, rats, and cats – is well known, threatening many of its endemic species.

In Europe, the UK had one of the highest numbers of established alien species, famous examples including the bright tropical green parakeets found ubiquitously across London and the gray squirrel that outcompeted the Christmas card-esque red. In the US, Florida was the top hotspot, with 26 percent of its fish, reptiles, birds, and mammals being non-native, including the Burmese python, iguana, and feral pig.

The researchers also found higher numbers of invaders in places that were wealthier and more densely populated, leading them to conclude that human introduction – whether accidentally, like stowaway rats literally jumping ship, or purposely releasing unwanted pets into the wild – is largely responsible.

The team concluded that global efforts to stem the tide of introduced species needed to focus on these areas identified in their study, with increased biosecurity measures, especially at points of entry like ports, and a review of currently proposed introductions.