Decadal changes in the documented number of intentional and unintentional introductions of alien species for 101 countries. Trends in introduction events (n = 18746) involving over 4800 alien species are shown as: a number of documented introduction events, and b the cumulative number of documented introduction events. An introduction event in this figure represents one species introduced outside of its known native range for the first time and into one of the 101 countries in the pool.