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Introduction pathways play a pivotal role in the success of Invasive Alien Species (IAS)—the subset of alien species that have a negative environmental and/or socio-economic impact. Pathways refer to the fundamental processes that leads to the introduction of a species from one geographical location to another—marking the beginning of all alien species invasions. Increased knowledge of pathways is essential to help reduce the number of introductions and impacts of IAS and ultimately improve their management. Here we use the InvaCost database, a comprehensive repository on the global monetary impacts of IAS, combined with pathway data classified using the Convention on Biological Diversity (CBD) hierarchical classification and compiled from CABI Invasive Species Compendium, the Global Invasive Species Database (GISD) and the published literature to address five key points. Data were available for 478 individual IAS. For these, we found that both the total and annual average cost per species introduced through the ‘Stowaway’ (US$144.9bn; US$89.4m) and ‘Contaminant’ pathways (US$99.3bn; US$158.0m) were higher than species introduced primarily through the ‘Escape’ (US$87.4bn; US$25.4m) and ‘Release’ pathways (US$64.2bn; US$16.4m). Second, the recorded costs (both total and average) of species introduced unintentionally was higher than that from species introduced intentionally. Third, insects and mammals, respectively, accounted for the greatest proportion of the total cost of species introduced unintentionally and intentionally respectively, at least of the available records; ‘Stowaway’ had the highest recorded costs in Asia, Central America, North America and Diverse/Unspecified regions. Fourthly, the total cost of a species in a given location is not related to the year of first record of introduction, but time gaps might blur the true pattern. Finally, the total and average cost of IAS were not related to their number of introduction pathways. Although our findings are directly limited by the available data, they provide important material which can contribute to pathway priority measures, notably by complementing studies on pathways associated with ecologically harmful IAS. They also highlight the crucial need to fill the remaining data gaps—something that will be critical in prioritising limited management budgets to combat the current acceleration of species invasions.

Introduction pathways play a pivotal role in the success of Invasive Alien Species (IAS) – the subset of alien species that have a negative environmental and/or socio-economic impact. Pathways refer to the fundamental mechanism that leads to the introduction of a species outside of its native range – marking the beginning of all alien species invasions. Increased knowledge of pathways is essential to help reduce the flow and impacts of IAS and ultimately improve their management. Here we use the InvaCost database, a comprehensive repository on the global monetary impacts of invasive alien species, combined with the CBD hierarchical classification of introduction pathways to address four key questions: (i) Are particular IAS introduction pathways economically impactful? (ii) How are costs taxonomically and spatially distributed across pathways? (iii) Are there differences in costs between species introduced intentionally and unintentionally? and (iv) is there a relationship between the number of possible introduction pathways of IAS and their costs? We found first that both the total and average cost of species introduced through ‘Stowaways’ (US$144.9bn; US$89.4m) and ‘Contaminants’ pathways (US$99.3bn; US$158.0m) were more costly than species introduced primarily through ‘Escape’ (US$87.4bn; US$25.4m) and ‘Release’ (US$64.2bn; US$16.4m). Second, insects drove the costs of unintentional introductions whilst mammals drove the costs of intentional introductions; ‘Stowaways’ had the highest costs in Asia, Central America, North America and Diverse/Unspecified regions, whilst Antarctic-Subantarctic and Oceania incurred the greatest costs from species introduced through ‘Release’. Third, the cost of species introduced unintentionally is more than double the cost of species introduced intentionally ($192bn vs. $90bn). Equally, species introduced unintentionally cost more on average than species introduced intentionally in terms of damage, management, and mixed costs. Finally, the total and average cost of IAS was not related to their number of introduction pathways. Our findings provide important material for the targeting of priority pathways - something that will be critical in prioritising limited management budgets to combat the current acceleration of species invasions.