Invasive alien species ‘travelling around the world at unprecedented rates’

Invasive alien species are travelling around the world at “unprecedented rates” because of humans, threatening native plants and animals with extinction while damaging human health and livelihoods, scientists have warned.

Their cost to the world economy is estimated to be at least 423 billion dollars (£336 billion) a year, having quadrupled every decade since 1970, though this has been described by the authors as “a huge underestimate” and “the tip of an iceberg”.

Animals, plants and other organisms that have been introduced to other ecosystems by humans intentionally or otherwise are classified as alien species, though not all become invasive.

They can be mitigated, prevented, through effective management and we really stress that the most important management is prevention, preventing the species reaching new areas in the first place

Of the 37,000 alien species documented by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) in a major report published on Monday, 3,500 have become invasive, with 66% of those found on indigenous lands.

They are present on every continent on Earth including Antarctica and are one of the main causes of biodiversity loss alongside climate change, direct exploitation, land- and sea-use change and pollution.

Some species can take years to become a problem after arriving in a new area, with the scientists advising that prevention and surveillance are the best weapons against new invasions.

The Assessment Report on Invasive Alien Species and their Control took four years to compile, with 86 scientists from 49 countries reviewing thousands of documents while hearing from indigenous communities, some of which are struggling to hold on to their cultural identities because of biological invasions.

The scientists estimate that invasive species have caused or contributed to 60% of global extinctions, with nearly all of them happening on islands, which are the most vulnerable because they have unique ecologies that may have had no contact with the rest of the world for thousands of years before humans arrived.

Governments around the world have committed to protecting 30% of the Earth’s land and seas for nature by 2030, and 143 of them have approved the new IPBES report as providing some of the scientific knowledge towards achieving this goal.

Professor Helen Roy, of the UK Centre for Ecology and Hydrology and one of the report’s co-chairs, said: “We really believe that this assessment is one of hope.

“There are things that people can do to tackle the threat of invasive alien species.

“They can be mitigated, prevented, through effective management and we really stress that the most important management is prevention, preventing the species reaching new areas in the first place.

“But if they do reach new areas, then being prepared and having early detection and rapid response is absolutely critical.”

The water hyacinth was found to be the most widespread invasive alien species worldwide, alongside the black rat and harlequin ladybird.

In the UK, the North American grey squirrel has pushed the native red squirrel to the fringes of the British Isles, outcompeting it for food while carrying a disease lethal to the red squirrel but which does not affect the grey squirrel.

Although loved by gardeners, rhododendron is another invasive alien species in the UK, having originated in the Himalayas.

It harbours a fungus that kills other plant life and in Scotland it is rapidly displacing many other species.

Scientists are concerned that climate change will make conditions favourable for other alien species in the UK and they are particularly wary of the Asian hornet, as its sting can cause an allergic reaction in some people.

Giant hogweed also grows in the UK and it can cause blisters on the skin while other plants that can trigger hay fever and insects carrying diseases may become more common in future.

The scientists have asked people to be on the lookout for invasive species such as the Asian hornet and to report them so they can be eradicated.

Prof Roy said: “We are talking in this particular context, not about those range-expanding species that are native, but about invasive alien species that are being moved by humans at really unprecedented rates and then we’re mixing them together in different ways.

“Of course, extinction is such an important thing to be considering, but also it’s really important to think about the extinction of interactions, when one species is displacing another or reducing its numbers to such very low abundance.

“We are causing ecological changes that perhaps will lead to really quite unpredictable outcomes in terms of the functioning of these ecosystems and the benefits we receive from them.”