Invasive species are often threatened in their natural habitat

Non-native species introduced by humans are one of the main causes of global species decline: they are partly responsible for 60% of species that have disappeared worldwide in recent decades. Non-native mammals of Central Europe include species such as the Norway rat, mouflon and mink.

Now, a study by biologists from the University of Vienna and the Sapienza University of Rome shows that some of these species introduced by humans are themselves endangered in their regions of origin . The study was published in the current issue of the journal Conservation letters.

The globalization of the Earth contributes to the introduction of many animal and plant species into new regions of the world. Invasive species can displace native species through competition or transmit new diseases. However, at the same time, some of these non-native species are threatened with extinction in their native ranges.

This creates a conservation paradox, because the question now is whether non-native populations of threatened species in their native ranges should be protected or combatted? However, it was not yet clear how many non-native mammal species this paradox actually applied to. In the new study, scientists have now quantified this in order to get closer to the answer to this paradox.

In total, 230 species of non-native mammals have been introduced to new areas by humans and settled there permanently. “We wanted to know how many of these species are threatened in their own country,” explains Lisa Tedeschi of La Sapienza University and the University of Vienna, lead author of this study.

Scientists were able to show that 36 species of non-native mammals are threatened in their country of origin and therefore fall under this conservation paradox. “This high figure surprised us a lot, because we assumed that invasive species were also common in their area of ​​origin,” continues Tedeschi.

One of the endangered native mammal species is the crested macaque, whose numbers have declined by 85% in its original range in Sulawesi since 1978, while it has spread to other islands in Indonesia and there are stable populations. The wild rabbit is threatened in Europe, while in other parts of the world, such as Australia, it has very large introduced populations, much larger than those in Europe.

Most endangered native species are native to tropical Asia; in many cases their decline is the result of massive rainforest destruction and overhunting. Populations introduced by humans could therefore help prevent the extinction of these species.

Globalization: Nature conservation faces a difficult task

When assessing global extinction risk, occurrences of species that do not live in their native range are currently not considered. In the present study, however, the researchers were able to show that the situation of certain endangered species would improve if non-native occurrences were also taken into account.

“For 22% of the species analyzed, the global extinction risk would be reduced if non-native occurrences were also included in the assessment,” says biodiversity researcher Franz Essl from the University of Vienna, one of the lead authors of the study. According to the scientists, this result highlights the considerable importance of non-native populations for the survival of endangered species, especially when the threat level is high in the natural range.

However, the inclusion of non-native populations of these species in the threat assessment also carries risks: for example, less attention is paid to protecting threatened populations in the native area. Additionally, non-native populations can have negative effects on other species.

“The main focus must continue to be on protecting species in their native area. However, it is likely that in the future more species will be threatened with extinction in their native area and will have better chances of survival in the new area.

“This imposes on nature protection the difficult task of weighing opportunities and risks,” concludes Franz Essl. “It is also an imprint of the globalization of species distribution.”