Katelyn T. Faulkner^1,2, Mark P. Robertson2 and John R. Wilson^1,3

¹South African National Biodiversity Institute, Kirstenbosch Research Centre, Claremont 7735, South Africa
²Centre for Invasion Biology, Department of Zoology and Entomology, University of Pretoria, Hatfield 0028, South Africa
³Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Matieland, 7602, South Africa

e-mail: katelynfaulkner@gmail.com

Biological invasions often transcend political boundaries, but the capacity of countries to prevent introductions varies. How this variation in biosecurity affects the invasion risks posed to the countries involved is unclear. We aimed to improve the understanding of how the biosecurity of a country influences that of its neighbours. We developed six scenarios that describe biological invasions in regions with contiguous countries. Using data from alien species databases, socioeconomic and biodiversity data, and species distribution models, we determined where 86 of the 100 of the world’s worst invasive species are likely to invade and have an impact in the future. The predicted invasions were classified according to the scenarios and information on the capacity of countries to prevent invasions was used to determine whether the invasions are likely to be avoided. Introductions of the 86 species could result in 2523 future invasions, most of which could have impacts and are unlikely to be prevented as the invaded countries have a low capacity to prevent invasions. Of the invasions, 38.6% could spread from the country in which the species first establishes into neighbouring countries. For almost a third of the invasions (31.4%), countries where impacts could occur will rely on a neighbouring country’s biosecurity. Most of these invasions are unlikely to be prevented as the country of first establishment has a low capacity to prevent invasions or has little incentive to do so as there will be no impact in that country. Invasions that conform to the latter scenario are particularly concerning, as their management could cause conflicts of interest and as many of these invasions were predicted to occur in developing regions where their impacts are likely to be most severe. Therefore, regional co-operation and communication are required to prevent the vast number of biological invasions that could occur in the future.