No sign of slowing: Alien species on the rise

The number of new instances of non-native species documented is increasing around the globe — growth that shows no sign of slowing.


The introduction of alien species can disrupt ecosystems and even cause local extinctions.

Hanno Seebens at the Senckenberg Biodiversity and Climate Research Centre in Frankfurt, Germany, Franz Essl at the University of Vienna and their colleagues assembled a data set of 45,813 records, dating back to the 1500s, detailing the first arrival of an alien species.

They show that such ‘first records’ have increased in the past 200 years, from an average of 7.7 per year between 1500 and 1800 to a record 585 in 1996.

The rise in these records in the past 200 years was found in all taxa, with the exception of mammals and fishes, in which rates have declined in recent decades.

Alien numbers will probably continue to rise for years to come, despite efforts to curb them.

No saturation in the accumulation of alien species worldwide

Although research on human-mediated exchanges of species has substantially intensified during the last centuries, we know surprisingly little about temporal dynamics of alien species accumulations across regions and taxa.

Using a novel database of 45,813 first records of 16,926 established alien species, we show that the annual rate of first records worldwide has increased during the last 200 years, with 37% of all first records reported most recently (1970–2014).

Inter-continental and inter-taxonomic variation can be largely attributed to the diaspora of European settlers in the nineteenth century and to the acceleration in trade in the twentieth century.

For all taxonomic groups, the increase in numbers of alien species does not show any sign of saturation and most taxa even show increases in the rate of first records over time.

This highlights that past efforts to mitigate invasions have not been effective enough to keep up with increasing globalization.