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.