Invasive alien species are expected to contribute to significant numbers of global extinctions in the coming decades. This study assesses vulnerable bird and mammal species according to their contribution to global biological diversity and considers the consequences of projected species loss. The researchers conclude that declines in diversity and shifts in global species composition resulting from invasive alien species could have significant effects on existing ecosystems.

SCIENCE FOR ENVIRONMENT POLICY
Invasive alien species (IAS) are a notable cause of global species extinctions. Historically,assessments of the threat posed by IAS have focused on numbers of species threatened, however, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) recommends that conservation assessments address ecological and evolutionary components. This study measured biological diversity through differences in evolutionary history, feeding behaviour, activity patterns and body size in mammals and birds to evaluate the potential ecological impacts
of extinctions associated with IAS.

The study classed as ‘invasive-threatened’ any species listed as threatened on the International Union for the Conservation of Nature Red List of Threatened Species (IUCN Red List) for which it lists invasive species as one of the threats. The researchers found that 207 out of 5 708 IUCN-listed mammal species and 499 out of 10 965 IUCN-listed bird species are invasive-threatened, and that most of these also face other threats.

The researchers measured trait diversity (TrD) using five variables: body mass, habitat breadth (number of habitats used), foraging level (such as ground, arboreal or aerial), main diet (such as fruits and nectar, invertebrates or omnivorous) and time of activity (such as nocturnal or diurnal).
They also calculated phylogenetic diversity (PD, difference in evolutionary history) with reference to established evolutionary trees. Then they considered several extinction scenarios using the probability of extinction given in each IUCN Red List category to calculate likely extinctions of invasive-threatened species in the next 50 and the next 100 years. They compared these scenarios with the equivalent loss of randomly-selected species