Invasive alien species are among the main causes of global biodiversity loss, contributing to 60% of the species extinctions recorded in recent decades. In Central Europe, non-native mammals include the Norway rat, the mouflon and the American mink. A study by biologists from Sapienza University of Rome and the University of Vienna revealed that some of these human-introduced species are threatened with extinction in their native ranges. The results of the study were published in the latest issue of the scientific journal Conservation Letters.

Increasing globalisation has facilitated the spread of many animal and plant species to regions of the world where they did not originally belong. Invasive species can endanger native species through competition for resources or the transmission of new diseases. However, some of these invasive species turn out to be at risk of extinction in their native ranges. This phenomenon raises an interesting conservation paradox: is it right to protect these species in their native ranges, despite the damage they can do elsewhere? Until now, it was unclear how many threatened mammal species were involved in this paradox. The recent study has quantified the phenomenon, taking a step forward in understanding this complex issue.

Invasive alien species are among the main causes of global biodiversity loss, contributing to 60% of the species extinctions recorded in recent decades. In Central Europe, non-native mammals include the Norway rat, the mouflon and the American mink. Currently, humans have introduced 230 species of non-native mammals into new areas of the world, where they have become permanently established.

“We asked ourselves how many of these species are also threatened in their native ranges”, says Lisa Tedeschi, lead author of the study, affiliated with Sapienza University of Rome and the University of Vienna. “We found that 36 of these species are threatened in their native ranges, thus falling into the so-called conservation paradox. This number surprised us a lot”, Tedeschi points out. “We initially thought that alien and invasive species were common even in their native ranges”.

A prime example of an endangered mammal in its native range is the Cynopithecus (or crested macaque), whose population in Sulawesi, Indonesia, has collapsed by 85% since 1978. However, the species has spread to other Indonesian islands, where stable non-native populations can be found. A similar case is that of the wild rabbit, endangered in Europe, but with very large introduced populations in other parts of the world, such as Australia, which far outnumber those in Europe.

Most of the threatened species in their native range are found in the tropical regions of Asia, where massive destruction of rainforests and intensive hunting are the main causes of decline.

“The South-East Asian region represents the global hotspot of extinction risk for mammals”, explains Carlo Rondinini of Sapienza University of Rome, coordinator of the research group. “Trends in recent decades and projections for the future suggest that conserving endangered mammals in this region will be very complex. For this reason, alien populations of threatened species in their native range could in some cases represent an extra card to prevent their extinction”.

Currently, populations of species living outside their native range are not considered in global extinction risk assessments. This study, however, showed that including non-native populations could improve the risk classification for some species.

“For 22% of the species analysed, the risk of global extinction would be reduced if non-native populations were also taken into account”, says Franz Essl, from the University of Vienna and of study coordinator. According to the researchers, these results highlight how crucial non-native populations can be for the survival of threatened species, especially when their habitats of origin are severely compromised.

However, the inclusion of non-native populations in the risk assessment also presents critical issues. For example, it may diminish the focus on protecting threatened populations in their native range. Furthermore, non-native populations may harm other local species, contributing to new ecosystem imbalances.

"The priority must remain to protect species in their native habitats," says Essl. "However, in the future we are likely to see more and more species that are threatened with extinction in their native range, but have a better chance of survival in new areas. This presents biodiversity conservation with the complex task of balancing risks and opportunities. These dynamics reflect the profound impact of globalisation on the distribution of species".

References:

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

Further Information

Carlo Rondinini
Department of Biology and Biotechnology "Charles Darwin"
carlo.rondinini@uniroma1.it

Lisa Tedeschi
Department of Biology and Biotechnology "Charles Darwin"
lisa.tedeschi@uniroma1.it