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UNDERSTANDING THE FACTORS THAT DRIVE THE TRADE IN ALIEN SPECIES HELP US TO PREDICT AND UNDERSTAND BIOLOGICAL INVASIONS

Understanding why and how species arrive in a new area can help us to understand invasion patterns and identify potential future invaders. Reptiles are becoming increasingly popular as pet species and this trend has been linked to an increase in the number of alien reptiles establishing non-native populations around the world. Although there are relatively few incidences of alien reptile species establishing populations in South Africa, there is concern that the increase in trade of these species in the country could lead to problems in the future.

Nicola van Wilgen (a PhD student at the C·I·B), Dave Richardson and John Wilson (C·I·B core team members), and collaborators from the Australian Centre of Excellence for Risk Analysis reviewed the status of alien reptiles in South Africa. Their paper on “Alien invaders and reptile traders: What drives the live animal trade in South Africa?”, published in the journal Animal Conservation, examines the presence and abundance of alien reptiles in the South African pet trade.

The paper revealed some interesting and important patterns. Import trends indicate that species from specific families are favoured above others, specifically those from the families Boidae, Chameleonidae, Elapidae, Pythonidae, Testudinidae and Viperidae. Of these, chameleons, boas and turtles are popular pets, while vipers and elapids are more commonly kept for display purposes in zoos and parks. Further import biases exist within families. For example, in the chameleon family, species with larger body sizes are more likely to be imported than smaller ones. These biases are important to consider when identifying traits linked to species “invasiveness” or the ability to establish. One might observe that larger bodied species are more likely to invade, but this could merely be as a result of larger-bodied species preferentially being introduced.

Species abundance is also very important. The risk of a species becoming established and invasive is dramatically increased with increasing propagule pressure (the number of individuals introduced as well as the number of introduction events). Therefore characterizing trade volume can help to identify potential problem species. This study thus also attempted to explain the abundance of reptile species traded in South Africa in terms of the presence or absence of specific species traits. The authors found that species with certain traits are more popular than others: Venomous and expensive species, though a curiosity, are traded in low numbers, whereas species that are easy to breed and handle or are large, colourful or patterned are preferred. Species that are popular as well as being suited to local environments are a specific problem and the information gained through this study can be used to inform policy development and direct management efforts.

Two of the key steps for management identified in earlier work [click here to read this] were to determine which species are presently kept and traded in South Africa and then to assess which of these species has a high likelihood of establishment or poses a threat to biodiversity, ultimately designing tools to evaluate the risk of species not yet here, but desired for import.

Now that the alien species present in the country have been identified, managers are in a position to start evaluating which of those species traded in high numbers pose significant threats to biodiversity and regulate their trade accordingly. Furthermore, it is also possible to predict the probable popularity of species that are not yet here by evaluating their likely abundance based on their physical and trade attributes. This information will form an important component of risk assessment for future imports.