Quantifying global colonization pressures of alien vertebrates from wildlife trade

Abstract

The global trade in live wildlife elevates the risk of biological invasions by increasing colonization pressure (the number of alien species introduced to an area). Yet, our understanding of species traded as aliens remains limited. We created a comprehensive global database on live terrestrial vertebrate trade and use it to investigate the number of traded alien species, and correlates of establishment richness for aliens. We identify 7,780 species involved in this trade globally. Approximately 85.7% of these species are traded as aliens, and 12.2% of aliens establish populations. Countries with greater trading power, higher incomes, and larger human populations import more alien species. These countries, along with island nations, emerge as hotspots for establishment richness of aliens. Colonization pressure and insularity consistently promote establishment richness across countries, while socio-economic factors impact specific taxa. Governments must prioritize policies to mitigate the release or escape of traded animals and protect global biosecurity.

Fig. 1. Venn Diagram of species assembled (total 7780 species) from different data sources for the live wildlife trade based on GLVTD.

The number of species contained within each data source is given in parentheses. CITES: CITES Trade Database; LEMIS: the United States Fish and Wildlife Service’s (USFWS) Law Enforcement Management Information System; ISIS: International Species Information System; OTAPS: the dataset obtained from online trade and physical stores. The numbers in the diagram indicate the number of species in different sets in a data source or the intersections among multiple data sources. The figure is created by the VennDiagram package in R (Venn Diagram in Supplementary Code 1).

Fig. 2. Proportions of traded alien species and establishment in extant vertebrates.

The blue bar represents the proportion of traded species among all extant species; the red bar indicates the proportion of alien species among all traded species; the green bar shows the proportion of traded species among all established species; the yellow bar displays the proportion of established species among all traded alien species. Source data are provided as a Source Data file. The figure is created by Excel.

Fig. 3. The geographical distribution of alien vertebrate richness in trade (included established and unestablished species, total 6,664) and establishment richness (total 814 species) across the globe (data from GLVTD).

The figure is created by ArcGIS; (a) alien vertebrate richness (also see Supplementary Data 2 for original data); (b) establishment richness (Supplementary Data 4). Versions with alternative colour schemes are provided with Fig S2e–i and Fig S3e–i in Supplementary Information.

Fig. 4. Box plot of alien richness versus native richness in live wildlife trade across 193 countries (n = 193).

AR and NR represent alien species richness and native species richness, respectively. The black line and Χ inside the box indicate the median and mean, respectively. The bottom and top borders of the box represent the first and third quartiles. The vertical dotted lines outside the box represent the upper and lower limits. The outliers are represented as dots. Source data are provided as a Source Data file. The figure is created by Excel.

Fig. 5. Network analysis of the global flows of traded alien vertebrates (total 6,664 species) and established alien vertebrates (total 814 species) among 8 economic regions.

A unique colour indicates a region where species are native. The ribbons show the flows of species linked from native (no gaps) to alien regions (with gaps), with the size of ribbons representing the volume of species flow (the same species may be counted multiples due to its origination from multiple regions or its trade in multiple regions). The tick marks on unique colour segments indicate absolute number of species that are imported or exported from a region. The figure is created by the dplyr, circlize and reshape2 packages in R (Network analysis in Supplementary Code 1). a Traded alien vertebrates; (b) established alien vertebrates.