Invasive naturalized species will continue to spread globally

A new study led by Henry Häkkinen from the University of Exeter highlights a critical ecological issue. The researchers predict that naturalized species, those that are not native but have established themselves in new locations, possess the potential to spread even further into suitable habitats globally. 

The study explores the dynamics of how naturalized species, including plants, birds, and mammals, have managed to extend their reach beyond their native regions.

What drives species invasions?

“Understanding and predicting the spread of introduced species is one of the key conservation and ecological challenges of the 21st century,” wrote the study authors.

“However, we know little about what causes the introduced range of some species to increase rapidly, while other species remain in small, isolated populations years after establishing self-sustaining populations.” 

“This major gap in our understanding prevents us from understanding how much of invasive spread is due to characteristics of the invader or the invaded environment.” 

Imminent threat of naturalized species

The researchers said the most imminent threat is posed by the many thousands of species that are naturalized outside their native range and may continue to spread much more widely. “However, there is a surprising lack of attention paid to the potential spread of already-naturalized species.” 

“Without understanding what has affected the spread of these species historically, we can assess neither which species are likely to spread further nor the geographic regions that will be most affected.”

Focusing on 833 naturalized plants, birds, and mammals, the researchers have identified the terrestrial areas most susceptible to future colonization by these species. Their findings highlight North America, Eastern Europe, and Australia as particularly vulnerable regions. 

The study reveals a significant potential for the further spread of naturalized birds in North America, mammals in Eastern Europe, and plants in both these regions as well as in Australia. 

Potential spread of naturalized species

“The potential spread of naturalized species appears greatest in regions that are already heavily invaded, i.e., North America, Australia, and Europe. However, already-naturalized species also threaten areas of the world thought of as less invaded,” wrote the study authors.

“In South America and Southern Africa around 200 regionally naturalized plants have the potential to spread widely – a number comparable to that in Australia and China, which have historically borne the brunt of biological invasions.”

“Nonetheless, the potential for regionally naturalized species to spread in sub-Saharan Africa and the north of South America is lower than one would expect from the globally high numbers of species naturalized there. This is potentially encouraging given the recent increases in regional trade and transportation infrastructure in these regions that could increasingly facilitate the spread of naturalized species.”

Delay in expansion 

Despite having ample opportunities to expand, many of these species have not yet colonized all areas with a compatible climate. This delay in expansion suggests that some introduced species may not become problematic immediately but could pose risks after a lag period.

“Nearly all species we studied have yet to expand throughout most of the areas that are climatically suitable for them, within the biogeographic regions where they have naturalized. This is despite substantial time to invade: 25% have been established for over 150 years,” noted the researchers.

Invasional meltdown

The experts also identified the key factors influencing the spread of naturalized species. They found that a species’ introduction history, its dispersal capabilities, and the presence of suitable habitats are more critical in determining its spread than its preferred habitat or interactions with local species. This insight is vital for understanding and predicting the movement of non-native species.

A concerning finding of the study is the concept of “invasional meltdown.” This phenomenon occurs when multiple introduced species collectively amplify their impact and ability to establish themselves in a new environment, potentially leading to devastating ecological consequences. 

While many of the species that were studied have a minimal impact on their own, their collective effect could be significantly more harmful.

Future implications of naturalized species

“Species invasions can devastate biodiversity, agriculture, and livelihoods, so it’s worrying that so many naturalized species seem poised to spread further,” wrote the researchers.

“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.”

The study is published in the journal PLoS Biology.

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