The impacts of human-facilitated introduction and range expansion of invasive alien species (IAS) on ecological and socioeconomic systems worldwide are undeniable. Managing and mitigating their damaging effects requires better understanding of the global spread of IAS.
In this study, researchers compiled a global list of known IAS plants and animals threatening ecosystems and verified the validity of species names against relevant taxonomic checklists. They then extracted more than 50 million occurrence records of these species from GBIF and other sources.
After excluding duplicates, records from native range, and species with less than 200 occurrences, they analysed the growth of 178 IAS using linear regression models individually, across higher taxonomic groups, and all species pooled together.
While some individual species showed signs of saturation, the overall results of the pooled species and taxonomic groups displayed patterns of exponential growth in records outside native ranges. The increase in number of records was higher in non-native ranges than native ranges when controlled for sampling effort.
For all species combined, the number of non-native occurrences was estimated to double in 14 years. Molluscs and crustaceans had the highest rates of increase in records with an estimated doubling time of just six years. The average rates for flowering plants were much lower, requiring 17 years to double.
At the continental level, North America had the most taxonomic groups (10 out 11) exhibiting exponential growth rates, followed by Europe (five groups), Asia and South America (three groups), Oceania (two groups) and Africa (one group). These results show that despite efforts to curtail spread, IAS are continuing to expand their ranges at alarming rates worldwide.