Global patterns in threats to vertebrates by biological invasions

Abstract

Biological invasions as drivers of biodiversity loss have recently been challenged. Fundamentally, we must know where species that are threatened by invasive alien species (IAS) live, and the degree to which they are threatened. We report the first study linking 1372 vertebrates threatened by more than 200 IAS from the completely revised Global Invasive Species Database. New maps of the vulnerability of threatened vertebrates to IAS permit assessments of whether IAS have a major influence on biodiversity, and if so, which taxonomic groups are threatened and where they are threatened. We found that centres of IAS-threatened vertebrates are concentrated in the Americas, India, Indonesia, Australia and New Zealand. The areas in which IAS-threatened species are located do not fully match the current hotspots of invasions, or the current hotspots of threatened species. The relative importance of biological invasions as drivers of biodiversity loss clearly varies across regions and taxa, and changes over time, with mammals from India, Indonesia, Australia and Europe are increasingly being threatened by IAS. The chytrid fungus primarily threatens amphibians, whereas invasive mammals primarily threaten other vertebrates. The differences in IAS threats between regions and taxa can help efficiently target IAS, which is essential for achieving the Strategic Plan 2020 of the Convention on Biological Diversity.

Keywords: alien species; biological invasions; non-native species; threatened species; vertebrates.

Figure 1.

Spatial distribution of IAS-threatened (CR, EN and VU IUCN Red List) mammals, birds, reptiles and amphibians, in absolute number (a) and given as a proportion of all threatened species (b). For instance, a proportion of 50% for a given location means that 50% of the threatened species there are threatened by IAS.

Figure 2.

(a) Maps of the distribution of CR, EN and VU IAS-threatened vertebrates per country, and occurrences of IAS-threat (red) versus other threats (grey). Note that only countries and islands are illustrated here where more than 25% of the threatened species are threatened due to IAS. (b) Boxplots showing the percentages of IAS-threatened species compared to all threatened species on islands versus mainlands.

Figure 3.

Number of IAS-threatened species compared to number of species threatened by other factors per country and taxonomic group. Please note the different scales of the two axes.

Figure 4.

(a) Top 7 of IAS that globally threaten the highest numbers of mammals, birds, reptiles and amphibians. (b) Spatial distribution of IAS that have been identified as threatening vertebrates and for which spatial distribution data were available (N = 197). We calculated Pearson's correlation coefficient between IAS distribution (here) and IAS-threatened vertebrates (combined figure of figure 1b): Pearson's r = −0.05.