Mapping the global state of invasive alien species: patterns of invasion and policy responses

Aim To use global databases to (1) provide a visualization of global geographical patterns of species invasions, origins and pathways and (2) depict the international uptake of legislative and policy responses to invasive alien species (IAS). Location Global. Methods Patterns of recorded species invasions and pathways of introduction were mapped and visualized using data from the Global Invasive Species Database (GISD) and the CABI Invasive Species Compendium (CABI ISC), along with associated legal instruments relevant to IAS compiled from the ECOLEX database. A novel indicator of the asymmetry between each country's 'ingress/egress' of IAS (kappa, K), was developed to further explore spatial patterns. Results Substantial variation in the spatial patterns of invasion was determined, with the Global North, some newly industrialized countries and small tropical islands being the main recipients of IAS and asymmetry (K) being highest in New World countries and small islands. Of the 1517 recorded IAS, 39% were introduced only intentionally and 26% only unintentionally, 22% both intentionally and unintentionally, while 13% had no information available. The dominant pathway for species invasions was horticulture and the nursery trade, with 31% of the species introduced outside of their natural geographical range. Large increases in legislation on IAS have occurred since the 1990s, particularly for those countries that have high numbers of species invasions. Main conclusions Clear global patterns in the distributions of IAS are determined, supporting arguments emphasizing the role of colonial history, economic development and trade in driving the human-mediated movement of species. Dominant pathways for species invasions are similar across different regions. Policy responses towards IAS show an increasing desire from the international community to act on species invasions. Current patterns suggest that Africa and Central Asia are priority areas for future IAS research and control.