Golden frog figurines displayed at the market in Valle de Anton, Panama, Saturday, April 26, 2008. The golden frog may be next in line in a string of several frog species that have gone extinct due to a non-native fungus known as Chytrid. Photo credit: AP Photo/Arnulfo Franco

History tells us that invasive species can do some serious damage: rats and cats munching a quarter of New Zealand’s birds out of existence, lion fish depleting Caribbean reefs of their colorful fish, a deadly fungus pushing entire orders of amphibians to the brink of extinction, the list goes on and on. And unfortunately, new research shows that the list of invasive species will likely keep growing into the 21st century. By investigating a global database of alien species, an international team found that the number of newly emerging non-native species has been increasing steadily for 500 years.

“We’ve been introducing species around the world for centuries, so you might think that we’re running out of species to introduce, but that doesn’t seem to be the case,” explained the study’s co-author, Tim Blackburn, from the University College London. “By collecting this huge database of more than 16,000 alien species, what we find is that [from 2000-2005] roughly a quarter of first occurrence records of alien species relate to species that have never been recorded as alien species before.”

Asian carp, an invasive species, pose a significant environmental and economic threat to the Great Lakes region. Photo credit: AP Photo/John Flesher, File

And it’s likely that this uptick in the spread of species will continue into the coming decades; “We have an ongoing trend over the past 500 years, and while it’s always a little bit dangerous to extrapolate beyond the limits of your data…I think we can assume that we’re still going to be getting a lot of new alien species that have never been seen as aliens before,” said Blackburn.

This study comes just a few weeks after a world registry of invasive species has been launched, with the goal of increasing awareness over the rising threat of globalization to biodiversity. Based on collaboration by hundreds of scientists, the registry will be a tool (much like the endangered species list) that helps countries set up regulations concerning potentially invasive species.

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A woman washes clothes in a river smothered by water hyacinth in China’s Sichuan province, Feb. 5, 2007. Since being introduced to China in the 1930's the weed has spread, smothering waterways across the country. China spends millions each year trying to rid its waterways of the weed, which competes with native plants for water and space. Photo credit: AP Photo/Color China Photo

Combating the coming invasion is made considerably harder by the fact that the largest factor behind the spread of non-native species is simply the economy. “The big driver of the overall increase in alien species introduction is simple trade,” said Blackburn, explaining that species are sometimes transported on purpose (for things like agriculture or the pet trade), but often they’re secret hitchhikers (seeds stuck on the bottom of shoes or microorganisms stowed away in the ballast water of ships). And as trade has increased, so have the opportunities to hitch a ride; the total amount of stuff that we’re moving around the planet has increased by an average of 4.7% every year since 1980, according to the World Trade Organization.

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Notably, not all non-native species are bad for their new environments. For example, in Spain, a non-native species of crayfish is now a main source of food for migratory birds, including some that are endangered. Another example is the dozen or so species of honeybees that were introduced to North America in the 16th century that farmers now depend on for crop pollination. Still, a large portion of non-native species have a negative impact on a region’s biodiversity and ecosystems; that’s when they become known as invasive (rather than alien or non-native), and when things go wrong, they can go really wrong.

“If you look at species that are already extinct, a significant number of them, perhaps even a majority of them, have been caused by moving things around the world,” said Elizabeth Kolbert, author of the Pulitzer Prize-winning book The Sixth Extinction, to Project Earth in April of 2017. “Just look at the case of New Zealand: the islands had all these very interesting birds that had evolved to be flightless because they didn’t have any predators; then the Māori brought rats, and that was the end of a lot of these birds, and then the British came in the 18th century, and they brought more rats, and cats, and weasels and all sorts of predators and now a very high proportion of New Zealand’s native birds are either extinct or just clinging to existence.”

New Zealand is frantically trying to rewind the clock before more of its endemic species go extinct; the government announced a plan to rid the islands of all rats, stoats and possums by 2050. But it turns out this is easier said than done, and the government is running into all sorts of complications, like killing the very birds they’re trying to protect with poison meant for rats.

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At the same time, New Zealand, along with its neighbor Australia, is trying to avoid future catastrophes by adopting some of the strictest biosecurity laws on the planet. These regulations dictate what sort of goods are allowed onto the islands, establish intense screening protocols to protect against uninvited hitchhikers, and these same regulations are what made Johnny Depp post that bizarre apology video for sneaking his dogs onto Australia via his private jet.

Johnny Depp and Amber Heard: Australian biosecurity

But while these laws are looked at as the gold standard of biosecurity, there’s a glaring flaw with them: these regulations tend to target species that are already recognized as harmful invaders, but as Blackburn’s study points out, a huge number of new non-native species are hitching rides across the planet, and it’s difficult to know what impact they’ll have until it’s too late.

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“Unfortunately, we’re more reactive than proactive,” said Julian Olden, an expert on invasion biology at the University of Washington, who was not affiliated with the new study. Olden went on to explain that researchers were considering more nuanced approaches to biosecurity that might solve this problem: “rather than taking a species-based approach to blacklisting potential invaders, we’re considering using the traits or attributes that are typically associated with bad invaders, and then trying to restrain or restrict species that have those attributes.” Think racial profiling, but not racist and targeting animals rather than human migrants. So far, this sort of profiling is rarely implemented, but Olden is hopeful that with more research like Blackburn’s to catalog the spread of non-native species, policies that effectively combat the spread of harmful invaders will come about.

“When we think about invasive species, they’re not that much different than natural disasters: they occur infrequently but when they do occur they can be really devastating in terms of ecological damages,” said Olden. “We’re trying to stop these very rare but potentially devastating events, and if they’re occurring more frequently over recent decades, then it’s really important that we start to have our national policies and laws against invasive species reflect the science.”