In a just published international study, a team of scientists, including Sven Bacher of the University of Fribourg, have warned of the increasing threat posed by invasive alien species. Immediate action is necessary, they emphasise, to detect, stop and monitor the invaders.
Alien species are plants, animals or even microbes that have been deliberately or accidentally introduced by humans into areas where they do not naturally occur. Many of these species flourish exceedingly well in their new environment and so are able to reproduce similarly well, leading to harmful effects on the environment, the economy and human health.
Cause for concern
The study, just published in the scientific journal "Biological Reviews", is the result of a collaboration between scientists from 13 countries from across Africa, Asia, Australasia, Europe and North and South America. In it, the experts note that the number of invasive alien species is increasing at an alarming rate. Around the globe, more than 18,000 such species have already been recorded.
The research team attributes the rapid increase in biological invasions to the similarly increasing number and ever wider range of possible ways in which the alien species are able to spread, as well as to the related rise in global traffic. They also underline the role of possible new routes, such as the online trade in exotic animals or the opportunity of crossing oceans on small "rafts" made of plastic waste.
The role of climate change
However, the study also shows how other drivers of global change, such as climate change, changes in land use or international trade, facilitate the massive rise in invasive species in new areas. According to the researchers, species that, for example, arrived by ship, can now reproduce more easily in their new home thanks to climate change. In addition, the year-round opening of the Arctic Ocean to shipping, due to global warming, is enabling the movement of marine organisms between the Atlantic and Pacific Oceans.
As part of the initiative "World scientists' warning to humanity: a second notice"*, the study calls for an urgent change in human behaviour with regard to the treatment of the earth and living beings. The authors stress that biological invasions can definitely be controlled as well as mitigated. They point to relevant approaches that are working around the globe and make specific recommendations for better systems of control. For example, the introduction of stricter border controls, including x-ray machines and sniffer dogs, has led to a continuous reduction in plant pathogens in New Zealand.
Professor Sven Bacher of the University of Fribourg, one of the co-authors of the study, emphasises: "The more we know about invasive alien species and their behaviour, the better we understand the problems associated with them. The threats posed by these invasive species must be taken seriously. It is up to us, politicians and the general public to make the containment and control of this biological invasion a priority".
* World scientists’ warning to humanity
In 1992, a group of eminent scientists from around the world came together and wrote a letter pointing out that humanity was on a collision course with the rest of nature (Union of Concerned Scientists, 1992). 25 years later, Ripple et al. (2017) published an analysis of human behaviour and in this second warning they have come to the conclusion that humanity has not managed to make the necessary progress in dealing with the environmental-technological challenges. On the contrary, the researchers concluded that most of the problems have worsened.
The first appeal in 1992 was supported by 1,700 scientists. In 2017 more than 15,000 experts signed the declaration.
Examples of harmful invasive alien species
Water hyacinth (Eichhornia crassipes): The water hyacinth, originating in South Africa, was able to spread around the globe due to its decorative appearance. However, it causes great damage, especially to fishing and water supply systems. In East Africa, for example, the emergence of the water hyacinth destroyed fishing grounds in Lake Victoria.
Tiger Mosquito (Aedes albopictus): The Asian tiger mosquito, which has been spread through the international tyre trade, transmits various diseases, including West Nile virus and dengue fever.
Striped eel catfish (Plotosus lineatus): The venomous striped eel catfish is at home in the Indian and Pacific Oceans. Via the Suez Canal it has reached the Mediterranean where fishermen can be injured by its spines.
Cane toad (Rhinella marina): Cane toads were introduced in many countries for the control of biological pests, but eventually turned out to be pests themselves. The toads compete with native amphibian species for food sources and, because of their toxic secretions, lead to disease and death among native animals.
Canada goose (Branta canadensis): Canada geese are now widespread in Europe and represent a serious threat to native biodiversity. They also cause economic damage to agriculture and can present problems for aviation by colliding with aircraft.