Biological invasion: 3,500 alien species introduced by humans are causing multibillion-dollar losses and extinctions

A comprehensive international report warns that the economic costs resulting from these plants and animals have already soared to over $400 billion a year

A fisherman maneuvers among water hyacinth, an invasive plant that is killing fish in the Kenyan part of Lake Victoria.Nils Adler

In Spain, combating water hyacinth in the country’s rivers has required mobilizing the army. That’s because the plant spreads like wildfire and is very difficult to eradicate. Water hyacinth wreaks havoc from Lake Victoria, in Africa, to Indonesia, to Florida, in the United States. The plant tops the list of the planet’s 10 most-widespread invasive alien species. It is one example of the biological invasion that humans have both intentionally and unintentionally caused, resulting in significant damage to nature and multimillion-dollar economic losses.

Worldwide, this invasion represents an annual cost of $423 billion (over €390 billion at the current exchange rate), including economic losses and the expenses of efforts to eradicate these species. Biological invasion is also one of the five main causes of the biodiversity loss crisis that is plaguing the planet, according to IPBES Invasive Alien Species Assessment, which was released on Monday. The report is an exhaustive analysis prepared by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES); IPBES has connections to the United Nations, to which 143 countries belong. IPBES scientists argue that “invasive alien species have contributed solely or alongside other drivers to 60 per cent of recorded global extinctions,” and the species are also “the only driver in 16 per cent of documented global animal and plant extinctions.”

But how do these species become a threat to biodiversity? Through humans. “Alien species are being introduced by human activities to all regions and biomes of the world at unprecedented rates,” warns IPBES. Experts estimate that there are currently 37,000 established alien species, which have arrived with humans either deliberately or accidentally. Moreover, they are increasing at " an unprecedented rate of approximately 200 annually.” Of these, 3,500 are documented as harmful and classified as invasive alien species.

This report focuses on these species and was prepared by 86 experts from 49 countries, drawing on over 13,000 scientific references. “People and nature are threatened by invasive alien species in all regions of Earth,” they warn. As the authors explain, the alien species’ negative impacts “are increasing rapidly in all regions of Earth and are predicted to do so in the future. Even without the introduction of new species, existing populations of invasive alien species will continue spreading through all ecosystems.”

Costs to the economy and nature

One of the report’s purposes was to quantify the damage that invasive alien species cause. Many of them have been introduced for commercial purposes, but IPBES is blunt: “The benefits to people that some invasive alien species provide do not mitigate or undo their negative impacts, which include harm to human health (such as disease transmission), livelihoods, water security, and food security.” The scientists also note that “the global economic costs of invasive alien species have quadrupled every decade since 1970.″

Of the estimated $423 billion per year cost to the global economy in 2019, the vast majority (92%) stems from the invasive species’ negative impact on “nature’s contributions to people and good quality of life.” Specifically, “reduction in food supply [is] by far the most frequently reported impact.” The remaining 8% “is related to the management expenditures for biological invasions.”

Once again, water hyacinth represents a good example: “In Lake Victoria, artisanal fisheries mainly involving men, have declined following the introduction, establishment and spread of the invasive alien plant, Pontederia crassipes (water hyacinth), which has led to the depletion of tilapia,” says IPBES. This plant species also has negative consequences on energy (as it interferes with hydroelectric production) and water quality. In fact, water hyacinth also tops the list of invasive species with the greatest number of documented negative impacts.

Eliminating water hyacinth from the Guadiana River (Spain), in 2014. RN FOTÓGRAFOS

Biological invasion also causes significant harm to health, as diseases such as malaria, Zika and West Nile virus spread through invasive alien species of mosquitoes such as those of the genera Aedes albopictus and Aedes aegyptii. “Invasive alien species pose a serious threat to biodiversity and can cause irreversible damage to nature, including the extinction of species at the local and global scales; they also threaten human well-being,” Helen Roy, one of the report’s coordinators, said in a statement on Monday.

Biodiversity loss

Five years ago, IPBES produced a study on planetary species extinction that set off alarm bells. That analysis identified five major drivers of global biodiversity loss: changes in land use, the climate crisis, overexploitation of resources, pollution and invasive alien species. The governments that belong to IPBES asked scientists to prepare a case study, which is the report that was released today.

Experts point out that, of the total number of alien species, about 6% of plants, 22% of invertebrates, 14% of vertebrates and 11% of microbes are invasive. The authors also state that at least 218 invasive alien species have been responsible for over 1,200 local extinctions. After the common rattlesnake, lantana (a shrub, Lantana camara) and the common rat (Rattus rattus) are the second and third most widespread species in the world, with far-reaching impacts on humans and nature.

The difficulty of eradicating invasive alien species

In addition to describing the problem in detail, the IPBES experts were also charged with providing solutions to this growing problem. As the scientists point out, if things remain the same, “the total number of alien species is projected to further increase globally, and by 2050, is expected to be approximately 36 per cent higher than in 2005.”

The specialists warn that the problem is often ignored until it is too late, which is why early action is crucial. The report notes that experience has shown that “eradication has been successful and cost-effective for some invasive alien species especially when their populations are small and slow-spreading, in isolated ecosystems such as islands.” For example, over the past century, “there have been 1,550 documented examples of eradication on 998 islands, with success cited in 88 per cent of cases.” French Polynesia is a case in point; there, Rattus rattus (black rat), Felis catus (cat), Oryctolagus cuniculus (rabbit) and Capra hircus (goat) have been successfully eradicated.

Things become more complicated when dealing with locations beyond islands, especially in marine ecosystems. Alien plants are also more difficult to eradicate “because of the longevity of dormant seeds that can persist in soil.” The authors of the report add that “when eradication is not possible for different reasons, invasive alien species can be contained and controlled, particularly in terrestrial and closed water systems.” Containment “can be achieved with physical, chemical and biological control measures” or some combination thereof. In the case of chemical methods, experts warn that they must be “implemented under regulatory compliance requirements,” and that society is increasingly less tolerant of such methods. For its part, “biological control has been very effective in controlling some invasive alien plants, invertebrates and, to a lesser extent, plant microbes and a few vertebrates”; but a biological approach to eradication can also have undesirable effects “if not well regulated.” In any case, the IPBES authors point out that, “overall, policies and their implementation have been insufficient in managing biological invasions and preventing and controlling invasive alien species.” They add that “most countries (80 per cent, 156 out of 196) have targets for the management of biological invasions within their national biodiversity strategies and action plans,” but “only 17 per cent of countries have national legislation for biological invasions.” The report also says that 45% of countries do not invest in managing biological invasion.

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