As globalization progresses, more and more animal and plant species are finding their way to other areas where they are not originally native. They often spread rapidly in their new home and are considered invasive. The paradox, however, is that some of these invasive species are threatened in their native habitat. Researchers have now examined how many invasive mammals this affects.
Invasive species pose a challenge to ecosystems in many regions around the world: the animal or plant newcomers often spread rapidly and can displace native species or introduce new diseases. Non-native species, such as the North American raccoon, which has also spread to Germany as a “captive escapee”, are partly responsible for 60 percent of the species that have become extinct worldwide in the past decades. Paradoxically, however, some of these alien species may themselves be threatened with extinction in their native habitats. This raises a conservation dilemma: Should these species be protected or combated in their new range? And how many invasive species are affected?
More than one in six non-native mammal species is threatened
To clarify these questions, a research team led by Lisa Tedeschi from the University of Vienna examined this using invasive mammals as an example. To do this, they evaluated a database in which the populations and distribution areas of 230 of the 242 known alien mammal species worldwide are recorded. The team compared this data with their status on the Red List of Endangered Species, which provides information about the extinction risk of endangered animal and plant species.
The result of the analysis: 36 of the 230 non-native mammal species are threatened in their native land. “We were very surprised by this high number, as we assumed that invasive species were also common in the area of origin,” explains Tedeschi. Of these 36 species, six are considered critically endangered, nine are critically endangered and 21 are endangered, according to the Red List. Non-native mammal species from the groups of even-toed ungulates, primates and diprotodontia, a subclass of marsupials that include, for example, koalas, wombats and kangaroos, are particularly badly affected.
Can the risk of extinction be reduced?
An example of an invasive mammal species that is threatened in its native range is the crested macaque. In its natural range on the Indonesian island of Sulawesi, its population has declined by 85 percent since 1978, but has spread to other Indonesian islands. In general, many of the species that are threatened in their native range come from tropical Asia. The reasons for this are the massive destruction of the rainforest and overhunting of the animals. But there is also a species in Europe that is threatened here but widespread elsewhere: the wild rabbit. After the English settler Thomas Austin imported 24 of these rabbits from England to Melbourne, Australia in 1859, wild rabbits spread rapidly, so that today there are around 200 million of them living in Australia.
These examples are important, among other things, because animal populations that live outside their original range are currently not included in the assessment of the global extinction risk. However, this can distort the risk assessment. “For 22 percent of the species analyzed, the global risk of extinction would be reduced if non-native occurrences were also included in the assessment,” explains senior author Franz Essl from the University of Vienna. However, this must be viewed in a differentiated manner: “The main focus must continue to be on protecting species in their home area,” emphasizes Essl. “However, it is likely that in the future there will be more species that are threatened with extinction in their native ranges and have better chances of survival in the new range. This is also a fingerprint of the globalization of species distribution.”
Source: University of Vienna; Specialist article: Conservation Letters, doi: 10.1111/conl.13069