VN April 2023

Vetnews | April 2023 21 Non-native species are transported and introduced to new geographical regions via numerous pathways, with the influence of each pathway shifting with fluxes in global trade (Hulme 2009; Essl et al. 2011). Most non-native species introductions fall under one of two types of invasion pathways: accidental introductions – for example, species that are spread by “hitchhiking” in or on ships and airplanes transporting commodities and people – and pathways in which the species are themselves a commodity (Hulme 2009). The latter group, exemplified by the exotic pet trade (WebPanel 1; Figure 1), has received increasing attention over the past decade as global markets for live plants and animals have grown, resulting in a concomitant uptick in the number of invasive species arriving via this route (Padilla and Williams 2004; Keller and Lodge 2007). Despite the pet trade producing several high-profile invasive species, such as the red lionfish ( Pterois volitans ) in the Caribbean Sea and the Burmese python ( Python bivittatus ) in south Florida, most research has focused on how the pet trade affects wild populations (being collected in the source countries) and introduces disease (being spread in the destination countries) (Lyons and Natusch 2013; Tella and Hiraldo 2014). Yet for some vertebrate groups, such as reptiles and amphibians, the pet trade has contributed the largest number of established non-native species worldwide (Kraus 2009). Research examining the pet trade’s role in producing invasive vertebrate species has remained diffuse and fragmented across disciplines and biological realms. We provide a comprehensive overview of the exotic pet trade as it pertains to vertebrate invasions, offering an understanding of the mechanistic processes while highlighting policy-relevant research gaps. Keeping vertebrate animals as household companions is extraordinarily widespread and growing in popularity globally (Ramsay et al. 2007; Carrete and Tella 2008; Bush et al. 2014). In the US, Australia, and the UK, over half of all households have at least one pet (Reaser and Meyers 2007). Although pet ownership per household is lower in China than in Western countries, China now ranks third among countries with the most pets, with a companion animal population of more than 100 million (Deng 2017). In the US, approximately 50% of pets can be considered “exotic” (APPA 2018): that is, pets without a long history of domestication, unlike dogs, cats, or horses (Figure 1; Bush et al. 2014). Exotic pet ownership has grown markedly in recent decades (Rhyne et al. 2012; Vall- llosera and Cassey 2017a). For instance, ownership of reptiles and amphib-ians in the US has more than doubled in less than two decades, from 2.4 million households in 1994 to 5.6 million in 2012 (APPA 2018). Keeping exotic pets is also geographically widespread. In Indonesia, Jepson and Ladle (2005) found that households were more likely to keep exotic pets, such as birds (22%) and fishes (9.5%), than they were to keep common domesticated pets, such as cats and dogs (3% or less). In some regions, such as Asia and South America, the exotic pet market is expanding rapidly as living standards improve (Ding et al. 2008; McNeely et al. 2009; Alves et al. 2010). Even if the per-capita demand for exotic pets worldwide remains stable, a growing human population and expanding middle class will lead to growing demand for vertebrates as exotic pets (Shepherd et al. 2007). Keeping exotic pets often strains the commonWestern definition of household “pet”. For example, Alves et al. (2010) reported that in Brazil “caged birds can be found on bar counters, in grocery stores, in shoe stores and in homes”, and Su et al. (2015) documented the range of bird species kept captive just long enough to be released as part of traditional Asian religious services. A recent trend in Chinese markets is the selling of live-animal keychains, in which live reptiles, amphibians, or fishes are kept in small pouches as jewelry; these animals either die, are removed from the pouches, and kept in captivity, or are released from the pouches into the wild (CNN 2011). For all of these examples, we categorize the animals as “exotic pets” because they are kept for non-utilitarian reasons (WebPanel 1) and pose an invasion risk when released into a new geographical locale. A complex market The trade in exotic pets can be legal, illegal, or both, as a species’ status may change as it moves across political boundaries within the commodity chain, and this variation in legal status creates a confusing array of terminology that has inhibited comprehensive understanding In a nutshell: • The worldwide market for exotic pets is large and growing, with implications for both the conservation of native biodiversity and the emergence of invasive species • The exotic pet trade pathway has already led to the establishment of several hundred non-native and invasive vertebrate animal species globally, and is poised to contribute to the establishment of even more in the future • Characterizing and reducing the invasion risk posed by exotic pets requires integrated research on social, economic, and environmental factors Figure 1: Exotic pets are those that are kept for non- utilitarian reasons and have a relatively short history of domestica- tion; examples are as diverse as the (a) central bearded dragon (Pogona vitticeps) and (b) pow-der blue surgeonfish (Acanthurus leucosternon). Dragons are sourced from captive breeding facilities and surgeonfish from the wild, and although nether species are considered threathened with extinction, it is illegal to export dragons from their native Australian range. >>> 22 Article