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TEASIng apart alien species risk assessments: a framework for best practices

This paper presents a new comprehensive risk assessment framework covering the entire process of biological invasions. The framework partitions the invasion process into 4 major stages: Transport, Establishment, Abundance, and Spread and also considers Impact (TEASI). For each stage, subcomponents are specified (e.g. number of species transported, habitat suitability) and dependencies described. The entire framework is not just described verbally but (for the first time) also mathematically. In a next step more than 300 risk assessment models from the scientific literature as well as risk assessment schemes used by practitioners (e.g. the risk assessment scheme used and recommended to member states by the European and Mediterranean Plant Protection Organization, EPPO) were analysed with respect to which framework components and subcomponents were included. The approaches published in the scientific literature were most often quantitative approaches that often focused on just one component, mostly the establishment (79%). In contrast, risk assessment schemes used in a policy context were mostly qualitative approaches that depend to a great extent on expert opinions and used scoring methodologies to derive an overall risk estimate. However, these approaches covered on average more components of the invasion process with a particular emphasize on impacts. The paper concludes that applied risk assessment schemes would benefit from the inclusion of more of the quantitative approaches presented in the scientific literature. This paper therefore presents not just the most comprehensive review of risk assessment models for invasive species to date but also introduces a novel framework to assess and improve existing approaches and for the development of future more accurate risk assessment schemes and their applications.