VN April 2023

Vetnuus | April 2023 24 the density of pet-owning households in cities and suburbs. As a result, cities tend to be hotspots for non-native animals that likely established after being kept as pets, especially if they are located in tropical and sub-tropical climates (eg Krysko et al. 2011). Figure 3: Cumulative (total) number of individuals across species imported as exotic pets for four taxonomic groups (amphibians, reptiles, birds, and marine fish). “Species rank” indicates the ranked number of imports for a species (ie a lower rank means more individuals were imported). Each black dot represents a single species and signifies the total cumulative sum (primary y-axis) of the number of individuals for all species imported into the US up to that rank, as derived fromUS Fish and Wildlife Service records. For each taxonomic group, few species predominate in the number of individuals imported, causing the points on the cumulative import ranking curve to aggregate after the first few species (ie those with the highest number of imported individuals). The numbers of species recorded as introduced (orange bars) or established (red bars) within either 50-species (amphibians) or 100-species (reptiles, birds, marine fish) incremented import volume bins are depicted as overlapping histograms (secondary y-axis).As such, most exotic pets introduced or established were imported at very high volumes (left-hand side of each panel), but a few introduced species have established wild populations despite being imported in relatively small numbers (right-hand side of each panel); note: secondary y-axes differ in scale between taxa (number of species established: amphibians = 3, reptiles = 43, birds = 46, marine fish = 1). See Romagosa (2014; birds, amphibians, reptiles) and Rhyne et al. (2012; marine fishes) for details on time period of import records and data sources for species’ non-native status. Research into what makes some exotic pet species more popular than others is central to predicting the risk that trade contributes to biological invasions. The exotic pet trade exhibits similar supply-and- demand characteristics to those of other markets. For instance, Vall-llosera and Cassey (2017b) showed that the price of pet birds increased with reduced availability. The number of pet birds held by any one consumer therefore varies widely, from several individuals of very rare birds to several thousand in the case of very popular species (Vall-llosera and Cassey 2017b). However, exotic pet consumers also exhibit “bandwagon” and “snob” effects, so price is only one factor in the purchase decision (Chen 2016). For bandwagon consumers, the demand for a particular item increases as more people purchase it, whereas snob consumers demand a particular item precisely because few other consumers own it. Bandwagon species tend to be traded at higher volumes and lower prices and are consequently more likely to be released by owners or to escape confinement, especially if they become difficult to maintain in captivity (Rhyne et al. 2012; Holmberg et al. 2015; Stringham and Lockwood 2018). Perhaps as a result of this dynamic, there is a consistent pattern in pet trade import data where a few species constitute themajority of individuals imported and sold, and these species are also the ones that are commonly introduced and regularly become established (Figure 3). For example, the green iguana (Iguana iguana) accounted for 46% of the total trade in reptiles in the US between 1996 and 2012 and non-native populations are now established across several US states (Figure 4; Robinson et al. 2015). Similarly, Rhyne et al. (2012) found that only 12% of marine fish species were imported into the US at volumes greater than 1000 individuals, but these species make up a disproportionate number of those that have been recorded as introduced (Figure 3). Livengood et al. (2014) found that the top 23 of 255 ornamental freshwater fish species imported into the US in 2010 accounted for 87% of total fish imports and have consistently topped the list of imports over a 30-year time span, disproportionately contributing to the set of established non-native fishes in the US. Yet there are also a few species that have been introduced or have become established despite being imported in relatively small numbers (Figure 3), suggesting other factors contribute to release (eg difficulty in care) or establishment (eg environmental matching). Knowledge gaps Existing research suggests that the exotic pet trade generates, and will continue to pose, a substantial invasion risk worldwide. The imperative to reduce this risk is growing as the impacts of several invasive species originating from the exotic pet trade become clear, and as this market experiences rapid future growth. We suggest four knowledge gaps that need to be addressed to reduce invasion risk. First, existing knowledge about market dynamics, supply and demand, and consumer behavior largely originates from – and focuses on – the US, Australia, and the EU. As these regions aremajor components of the exotic pet trade, the attention is warranted, but this ignores the massive rise in pet-keeping in emerging economies such as Brazil, China, and Southeast Asian countries, where there is every reason to believe the invasion risk is considerable (Alves et al. 2010). Existing evidence suggests that the motivations and practices associated with pet-keeping in these cultures differ substantively Article