According to the report published in September 2023 by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), invasive animals and plants play an important role in global species extinction. The publication examines current developments in the spread of introduced species, the causes and the impacts of the problem. In addition, the 86 researchers from 49 countries provide strategies and recommendations for action to combat invasive species.
Human activity as the cause
Humans are considered the cause of the spread of species into areas where they were previously not found. This has been happening for centuries—both intentionally and unintentionally. According to IPBES, human activities have introduced almost 37,000 alien species into regions and ecosystems around the world—and the number is still growing. Of these 37,000 introduced species, at least 3,500 are harmful invasive species that have a negative impact on ecosystems. In addition, the damage caused by invasive species results in global economic costs of more than 400 billion dollars each year.
Alongside changes in land and sea use (such as agriculture or fishing), the direct exploitation of animals and plants, for example for the food industry, climate change and pollution, the introduction of invasive species is among the five most important direct causes of biodiversity loss.
The authors of the report also point out that by no means all alien species become invasive. Invasive species are those that establish and spread in an alien area and have negative impacts on the ecosystem and, not infrequently, on the people living there.
60% of all extirpations are attributed to introduced species
(© Juan Carlos Fonseca Mata, CC BY-SA 4.0, via Wikimedia Commons)
According to IPBES, invasive species are one of the main factors in 60% of all documented extirpations of animals or plants. And in 16 percent of extirpations worldwide, invasive species are even the sole cause of local extinction.
In general, alien species have negative effects on native species and cause changes in the ecosystem by transforming habitats, which in turn has serious consequences for native species. The common water hyacinth (Pontederia crassipes), which originates from the tropics of South America and now, as a neophyte, overgrows waters worldwide and, for example, reduces fishing yields in Lake Victoria, is considered the world’s most widespread terrestrial invasive species. Black rats (Rattus rattus) are probably the best-known example when it comes to invasive animal species.
Invasive species cause the greatest damage on islands
The IPBES report shows that invasive species cause the greatest damage on islands. Such isolated habitats often have unique flora and fauna that are particularly sensitive to change. Before humans settled the islands, there were no land-dwelling mammals there such as rats, cats, rabbits, martens or possums—now they exist in large numbers.
The list of species that have gone extinct on islands because of introduced predators is long. This mainly affects birds: their lack of an escape response (island tameness), their flightlessness or their habit of nesting on the ground make them and their broods easy prey.
The extinction of the Lyall’s wren around 1895, an almost flightless songbird from Stephens Island, is said, for example, to have been mainly due to the presence of a cat on the small island. Today we know that Stephens Island was only the last refuge of Lyall’s wren. It had previously also occurred on New Zealand’s North and South Islands, where introduced Pacific rats (Rattus exulans) had already wiped it out in the 13th century.
Another example is the Laysan millerbird from the small Pacific island of Laysan. Rabbits and guinea pigs deliberately introduced to the island caused the small islet to be stripped bare within a very short time. The host plant of the Miller moth also disappeared, so the butterfly species, which by chance was also the main food source of the Laysan millerbird, died out in 1911, followed a few years later by the millerbird.
IPBES experts assume that the accelerated global economy, intensified and expanded changes in land and sea use, and demographic changes will lead to an increase in invasive alien species worldwide. Even without the introduction of new alien species, already established species will continue to expand their ranges and spread into new countries and regions. Climate change would further worsen the situation, because it allows some species to survive in other regions that are now warmer.
Prevention and eradication as measures against biological invaders
The researchers behind the report emphasize that the best and most cost-effective measure against biological invaders is prevention—stopping alien species from being able to open up new habitats in the first place, for example through import controls at the border. If it is already too late for that, containment, control and eradication of invasive species can be an effective method in certain situations to restore the ecosystem.
The eradication of invasive species has proven successful in the past, especially in isolated ecosystems such as islands; examples include the eradication of the black rat and the European rabbit (Oryctolagus cuniculus) in French Polynesia. The eradication of invasive plants, by contrast, is a greater challenge, since their seeds can remain unnoticed in the soil for a long time.
New Zealand is currently trying, under the motto Predator Free 2050 , to kill all alien rats, martens and possums, reported Der Standard in early September 2023. In this way, the extinction of further bird species is to be prevented. After New Zealand was settled from the 13th century onward by Polynesian seafarers—the ancestors of the Maori—and alien species were introduced as pets and food, at least 35 of the more than 200 bird species originally living there went extinct. Since 1800, at least another 16 species have been added. And today, roughly one third of New Zealand’s bird species are considered threatened or endangered.
While the various moa species (such as the North Island giant moa or the eastern moa) in New Zealand were wiped out within only one century after the arrival of the first settlers by hunting alone, the other bird species—for example the huia and the South Island kokako—died out primarily because of alien, introduced animals such as the black rat, the Pacific rat and the brown rat (Rattus norvegicus).
The most important figures from the IPBES report
- more than 37,000 alien species have become established worldwide so far
- another 200 alien species are recorded every year
- at least 3,500 of the alien species are considered invasive worldwide, including 1,061 plants,1,852 invertebrates,461 vertebrates and 141 microorganisms
- since 1970, the share of reported alien species has been 37%
- by 2050, an increase in alien species of 36% is expected
- the share of alien freshwater fish in the Mediterranean region is 35%
- in 60% of extirpated species, invasive species are considered one of the causes of extinction
- in 16% of globally extinct species, invasive alien species were the sole cause of their extinction
- 1,215 local extirpations of native species were caused by 218 invasive species (32.4% invertebrates, 50.9% vertebrates, 15.4% plants and 1.2% microorganisms)
- 90% of global extirpations on islands are caused by invasive species
- in 2019, the estimated annual economic costs of biological invaders amounted to 423 billion US dollars
- the success rate of the 1,550 eradication programs carried out on 998 islands is 88%
- the success rate of biological control programs for invasive alien plants and invertebrates is 60%
Examples of extirpations caused by invasive species as one cause of extinction
| Invasive species | Invasive in | Examples of extirpations |
| Red fox (Vulpes vulpes) | Australia, Tasmania | Broad-faced potoroo, Eastern hare-wallaby, Desert bandicoot, Lesser bilby |
| Rats (Rattus spp.) | worldwide | Maclear’s rat, Christmas Island rat, Darwin’s Galápagos mouse, Rodrigues giant day gecko, Kauai Oo, Norfolk ground dove, White-chested white-eye, Huia |
| Livestock such as domestic cattle (Bos taurus), domestic goat (Capra hircus) or rabbits (Leporidae) | worldwide | Galápagos giant rat, Desert rat-kangaroo, Auckland merganser, Miller moth, Laysan millerbird, Round Island burrowing boa |
| Stoat (Mustela erminea) | Australia, New Zealand | South Island kokako |
| Ceylon cinnamon (Cinnamomum verum) | tropical Asia, Seychelles, Caribbean islands | Brauer’s spiky harvestmen |
| Red swamp crayfish (Procambarus clarkii) | including Europe | Sooty crayfish, Ash Meadows killifish |
| Yellow crazy ant (Anoplolepis gracilipes) | Australia, tropical rainforest, Christmas Island (Indian Ocean) | Christmas Island forest skink, Christmas Island pipistrelle |
| Big-headed ant (Pheidole megacephala) | tropical and subtropical areas worldwide (such as the Hawaiian Islands) | Koʻolau spurwing long-legged fly, Hawaiian yellow-tipped tree snail, Budd’s Oahu tree-snail |
| Chytrid fungus (Batrachochytrium dendrobatidis) | Central and South America, Australia | Southern gastric-brooding frog, Splendid poison frog, Chiriqui harlequin frog, Rabb’s fringe-limbed treefrog, Corquin robber frog |
About the author: Doreen Fräßdorf
Doreen Fräßdorf is the author and publisher of artensterben.de. She researches and writes about extinct and endangered species in the modern era, with a focus on red lists, scientific studies, historical sources, and current conservation efforts. The goal is a clear, evidence-based overview of biodiversity loss and species protection.
She is also the author of a non-fiction book about extinct modern-era mammals.
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