Conservation paradox: Invasive species are often threatened in their native range

Non-native species introduced by humans are among the main causes of global species decline – they were partly responsible for 60 percent of the species that have become extinct worldwide in recent decades. In Central Europe, non-native mammals include species such as the Norway rat, the mouflon and the mink. Now a study led by biologists from the University of Vienna and La Sapienza University in Rome shows that some of these species introduced by humans are themselves endangered in their native range. The study has been published in the current issue of the journal Conservation Letters.

The globalization of the earth is contributing to the introduction of many animal and plant species into new parts of the world. Invasive species can displace native species through competition or transmit new diseases. At the same time, however, some of these non-native species are threatened with extinction in their native ranges. This creates a conservation paradox – because the question now is, should non-native occurrences of species that are endangered in their native range be protected or controlled? However, it was previously unknown how many non-native mammal species this paradox actually applies to. In the new study, the scientists have now quantified this in order to come one step closer to an answer to this paradox.

Many non-native mammal species are endangered in their native range

A total of 230 non-native mammal species have currently been introduced by humans to new areas around the world and have settled there permanently. "We were interested in finding out how many of these species are threatened even in their native range," explains Lisa Tedeschi from La Sapienza University and the University of Vienna, the lead author of this study. The scientists were able to show that 36 of the non-native mammal species are threatened in their original range and therefore fall under this conservation paradox. "We were very surprised by this high number, as we assumed that invasive species are also common in their area of origin," Tedeschi continues.

Invasion of foreign territories could even save some species from extinction

An important mammal species threatened in its native area is the crested macaque, whose population in its natural range on Sulawesi has declined by 85 percent since 1978, while it has spread to other islands in Indonesia and stable populations are found there. The wild rabbit is endangered in Europe, while in other parts of the world, such as Australia, it has very large introduced populations that are far larger than those in Europe. Most of the threatened species in their native range originate from tropical Asia, which in many cases is a result of massive rainforest destruction and overhunting. Human-introduced populations could therefore help these species to avoid extinction.

Globalization: nature conservation faces a difficult task

When assessing the global extinction risk, species that do not live in their native range are not currently taken into account. In the current study, however, the researchers were able to show that the threat situation of some species would improve if non-native occurrences were taken into account. "For 22 percent of the analyzed species, the global extinction risk would be reduced if non-native occurrences were also included in the assessment," explains biodiversity researcher Franz Essl from the University of Vienna, one of the main authors of the study. According to the scientists, this result underlines the considerable importance of non-native populations for the survival of endangered species – especially when there is a high threat pressure in the native area.

However, including non-native populations of these species in the threat assessment also entails risks – for example, that less attention is paid to the protection of threatened populations in their native range. In addition, non-native populations can have a negative impact on other species. "The main focus must continue to be on protecting species in their native range. However, it is likely that in the future there will be more species that are threatened with extinction in their native range and have better chances of survival in their new range. This presents nature conservation with the difficult task of weighing up the opportunities and risks," concludes Franz Essl. "This is also a fingerprint of the globalization of species distribution."

Original publication:

Tedeschi L., Lenzner B., Schertler A., Biancolini D., Essl F., Rondinini C (2024) Threatened mammals with alien populations: distribution, causes, and conservation. Conservation Letters (2024)
DOI: 10.1111/conl.13069

https://doi.org/10.1111/conl.13069Picture:

Fig. 1: The wild rabbit is endangered in its native Europe. In other parts of the world, such as Australia, this species has been introduced and has large populations. C: Alexis Lours