Due to global trade, plant and animal species are getting more and more easily into foreign areas by means of airplanes, ships and trucks. Compared to 2005, the number of alien species will increase by 36 percent worldwide by 2050, according to a comprehensive study. However, tighter regulations could slow the immigration of alien species, the researchers said.
All over the world, more and more animals and plants appear in locations where they were not originally native – in 2005 there were already more than 35,000 species worldwide. Many of them immigrate to new areas as “stowaways” with the shipping traffic and ballast water from ships, others are set free by the trade in exotic species. These invasive species become a problem when they spread dramatically and displace native species – for example because they grow faster or are more aggressive.
Strongest immigration in Europe
But will the number of alien species continue to increase in the future? Hanno Seebens from the Senckenberg Biodiversity and Climate Research Center has now dealt with this question together with an international research team. So far, studies on the spread of alien species have only covered individual groups of organisms or specific countries. However, the researchers now analyzed observations on the spread of all exotic animal and plant species in the last decades from 1950 to 2005 – worldwide. From this they developed a computer model that predicts the number of new, alien species by 2050.
The result: “The number of alien species will continue to increase,” summarizes Seebens. “Worldwide we will have an average of 36 percent more alien animals and plants in 2050 than in 2005.” This is regardless of whether it is immigration to the mainland, islands, water or land. According to the model, there are large regional differences. The researchers suspect the strongest increases in Europe: Compared to 2005, the number of alien species is forecast to increase by 64 percent by the middle of the century. In absolute numbers, the research team expects around 2,500 new species to immigrate to Europe. Other hotspots are the temperate latitudes of Asia, North America and South America. In contrast, scientists expect the lowest relative growth in alien species to be in Australia at only 16 percent.
Especially many arthropods and birds
The model also showed another trend: According to calculations, the invasion of new species in individual animal groups is gaining momentum. Seen worldwide, arthropods and bird species in particular will arrive in new areas faster than before – the former with an estimated 10,000 species. “The number of new, alien species of these selected animal groups will increase significantly in every region of the world by the middle of the century – in the temperate latitudes of Asia by as much as 117 percent,” explains Seebens colleague Franz Essl. This also applies to species invasion in Europe, according to Seebens. “Most of these are less noticeable newcomers such as insects, mollusks and crustaceans.”
“In contrast, there will hardly be any new, alien mammal species such as the raccoon that has already immigrated,” explains Seebens with regard to the species invasion in Europe. And from a global perspective, mammals and fish are comparatively slow to conquer new habitats. Here they suspect a total of around 800 species that migrate to new areas. In the temperate latitudes of Asia, the number of mammals is not increasing at all.
Species invasion can no longer be stopped
How can this increase in alien species be explained? “The predicted increase in alien species may not come as a surprise, given the steady increase over the past few decades and the lack of evidence of slowing globally,” say the scientists. For them, the causes of the invasion of species lie in global trade, tourism and traffic, which many plant and animal species offer as a means of transport to new habitats. Climate change, changes in land use and migration could also play a role.
According to the team, this increase will intensify over the next few decades. A reversal of the invasion of alien species is therefore not in sight: “We cannot completely prevent the introduction of alien species, because that would mean severe restrictions on trade,” says Seebens. “But with stricter regulations and their strict implementation, we can contain the flood of new species. The benefits of such measures have been proven by studies, ”states the biologist. “Especially in Europe, where the regulations are still relatively loose, there are still many ways of avoiding the introduction of new species.”
Source: Senckenberg Research Institute and Nature Museums, Article: Global Change Biology, doi: 10.1111 / gcb.15333