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Non-native species likely to continue spreading in North America, Australia and Europe

A species’ introduction, how it disperses and locations of suitable habitats all impact spread

Naturalized species, which are not native but have established themselves in new locations, have the potential to spread even further to suitable habitats in many parts of the world, we found in a paper published in open access journal PLOS Biology here.

Figure 1. Russel Lupins come from North America and are invasive in Europe, Australia and New Zealand. Despite being widespread, they could spread even further throughout the coasts of Australia and New Zealand, and much of Europe. Credit: Bernard Spragg, Flickr

Understanding and predicting where introduced species will spread is one of the key conservation and ecological challenges of the 21st century. However, we know little about what causes one species to spread rapidly, while another species remains in small, isolated populations for years. In the new study, Häkkinen’s team predicted the world’s terrestrial regions to which 833 naturalized plants, birds and mammals are most able to live, and investigated which factors have sped up or slowed their spread thus far.

We found there is huge potential for further spread of naturalized birds in North America, mammals in Eastern Europe and plants in North America, Eastern Europe and Australia. Furthermore, the history of a species’ introduction, its ability to disperse and the location of suitable areas are more important predictors of how a species has spread than its preferred habitat or how it interacts with other local residents.

Figure 2. Areas where regionally naturalised species could expand further. The numbers of species that could spread to each 10-minute grid-cell based on the cell’s climatic suitability for each species. Data:

Nearly all species we studied have yet to expand into all the areas with a suitable climate, despite having had plenty of time to invade. However, some introduced species may not become problematic until after an initial lag period.

Figure 3. Factors that correlate with how much of their potential range species have spread to. A solid line signifies the relationship is statistically significant, a dashed line means it was not.

Many of the species studied have a small impact on their environment, but these findings are still concerning. A region can experience “invasional meltdown” when multiple introduced species amplify their impact and ability to become established, potentially with devastating effects.

Species invasions can devastate biodiversity, agriculture, and livelihoods, so it’s worrying that so many naturalised species seem poised to spread further. But there is a glimmer of hope that invasions are much more limited than they could be – ecosystems may be holding off invaders better than we expected, and good management could help stem the spread.

Regan Early,

Henry Häkkinen,

Citation: Häkkinen H, Hodgson D, Early R (2023) Global terrestrial invasions: Where naturalised birds, mammals, and plants might spread next and what affects this process. PLoS Biol 21(11): e3002361.

Data and code. Code used to perform all analyses, derived data, and data necessary to replicate analyses are available at Shapefiles of each species estimated native and naturalised ranges, rasters of niche filling and expansion, diagnostic and validation statistics are too large to place in a repository and so are available upon request from ourselves. Please don’t hesitate to contact us.

Funding: HH was funded by the Natural Environment Research Council Great Western Four+ Doctoral Training Partnership (NERC GW4+ DTP) studentship program (Grant Number 102681). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

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