Unwanted pet goldfish grow to several times their normal size in US lakes. Crayfish and exotic birds are “set free” in religious mercy release practices across Asia. Terrapins, some perhaps bought by fans of Teenage Mutant Ninja Turtles, end up in wild ponds in Wales, Japan and across Europe. Cane toads, meanwhile, spread across Australia after being introduced to control pests in 1935.
While some non-native animals or “aliens” are released intentionally into the wild, others accidentally hitchhike on ships, planes, cars, trains, even ocean plastic. Either way, some will become “invasive alien species” that disrupt the natural balance of ecosystems, threatening native species and habitats, and driving biodiversity loss. In Northern Ireland, researchers at the school of biological sciences at Queen’s University Belfast are investigating the mechanics of these alien invasions in the hope that, by better understanding and predicting them, some of the most dangerous invasions can be limited in the future.
Wildlife populations naturally shift their ranges, but human activity accelerates the rate of biological invasions, as Dr Ross Cuthbert, a biologist at Queen’s, explains: “People can travel anywhere on the planet very quickly. We’re moving things farther, faster and at a higher frequency than ever before. We’re connecting lots of regions which historically have never had any ecological connection.” Cuthbert’s research focuses on how to predict the impact of invasive species, which can affect not just the environment, but the economy and people’s health as well.
In terms of damage and management, alien invasive species are already costing countries billions each year and, says Cuthbert, the figure could hit $1tn. Invasive species can destroy crops, forests and fisheries, causing as much damage as floods and storms. They are also a health issue because they can introduce diseases. The Asian tiger mosquito is spreading north across Europe as the climate changes. It has been detected in Kent – a relatively warm region with busy transport links, including the Channel tunnel. Cuthbert expects this mosquito to be established in the UK in the next decade: “It’s a vector of dengue, chikungunya, Zika – these mosquitoes are prolific human biters.”
Because invasive species cause a diverse range of consequences, research in this field is connected to many of the UN’s 17 sustainable development goals, which aim to eradicate poverty, reduce inequality and protect the planet against climate change by 2030. Environmental scientists at Queen’s take an integrated approach to align their research with these goals and particularly consider how invasive species relate to four of them (life on land, life below water, good health and wellbeing, climate action).
“About 37,000 non-native species have been introduced outside of their natural range globally,” says Cuthbert, who predicts that wildlife on different continents could eventually become homogenised unless there is more action to limit alien species. Of the 37,000 identified, more than 3,500 have become invasive.
Scientists at Queen’s investigate the flows of invasive species – where they come from and how they move about – to understand invasion dynamics and predict where in the world prevention measures should be prioritised. “It’s a transboundary issue. No one country can solve it. We need collaboration,” says Cuthbert. Global investment in biosecurity is essential, he adds: “We’re spending billions in damages, we’re spending way less on management.”
Jaimie Dick, a professor in the school of biological sciences, pioneered a method known as the functional response to predict the impacts of invaders. “By measuring the functional response, [how often a predator eats and how quickly it devours its prey] we can forecast which species could be problematic once introduced, compared to native species. Invaders tend to eat more than natives, so some invasive predators could eat things to extinction. Now, we can quantify that,” says Dick, who is proud that researchers around the world use this approach. Some scientists study gut contents, others use genetic techniques or count how many times a seal comes to the surface with fish. “You can measure this metric for all plants, animals, parasites – for any invader or native – whether they eat a food or absorb a nutrient. Our technique is universal.
“An invasive fish might eat twice as many native fish in an hour as the native predatory fish. An invader might be bigger or faster, and native prey won’t recognise the new predator, so the population crashes,” says Dick, who has used the functional response method to study golden apple snails that eat rice paddy crops in China, tree snakes in Guam that wipe out native birds and Asian clams that disrupt river wildlife in Ireland.
By combining a species’ functional response with how abundant it is, scientists estimate the damage it will have, then the biggest threats can be tackled. “Our science could be used to identify what to leave alone because they’re not doing any harm and what to eradicate. We’ve cracked the holy grail of being able to predict the impact of an invasive species – it might seem random but it’s all predictable.”
Cuthbert worries that current global targets to halve the impact of non-native species by 2030 won’t be met. “It’s hard to quantify how much invasion could happen before there’s some kind of massive, catastrophic consequence,” says Cuthbert, who wants to see specific targets to outline how many impacts, what kind of impacts and how many invasions should be allowed.
The problem will only worsen as wind, wave and climate patterns change, he says. Both Cuthbert and Dick expect mosquitoes to bring malaria back to Europe. Scientists at Queen’s are already monitoring livestock for midge-borne diseases such as bluetongue and Schmallenberg virus, and Dick is tackling Asian clam invasions in New Zealand using dry ice to induce thermal shock: “We’re recognised as people who do good science and are hands-on – New Zealand is investing in managing invasive species because they take this threat seriously,” he says.
In the UK, more action is urgently required, say Dick and Cuthbert. “With substantial investment, we would see the return in reduced damage and reduced economic costs. It’s difficult for us scientists to understand the lack of action,” says Dick, who would like the UK government to introduce a dedicated invasive species tsar “alongside a radical shift in thinking”.
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