Understanding and managing the introduction pathways of alien taxa : South Africa as a case study

For the effective prevention of biological invasions, the pathways responsible for introductions must be understood and managed. However introduction pathways, particularly for developing nations, have been understudied. Using the Hulme et al. (2008) pathway classification, we assessed the South African introduction pathways in terms of the number of introductions, the invasion success of introduced taxa, how the pathways have changed over time, and how these factors vary for vertebrates, invertebrates and plants. Pathway and date of introduction, region of origin, distribution and invasion status data for 2111 alien taxa were extracted from databases. Most alien and invasive taxa were deliberately introduced and subsequently escaped captivity or cultivation. Pathway prominence also varied temporally and across organism types. Vertebrates and plants were largely escapes and although most plant escapes have become invasive, this is not the case for vertebrates. However the number of new plant and vertebrate escapes has increased over time. Invertebrates have been deliberately released or unintentionally introduced as contaminants or stowaways. For invertebrates the number of release, contaminant and stowaway introductions has increased, and most contaminants and stowaways have become invasive. As effective screening procedures are in place for invertebrates released for biological control, the major threats for South Africa are from vertebrate and plant escapes and invertebrate contaminants and stowaways. We recommend improvements to risk assessment and education to prevent escapes, and prioritised inspection strategies to reduce stowaway and contaminant introductions. Finally, as introduction pathways and introduced taxa change temporally, biosecurity decisions need to be informed by information on current and future pathways.