The Continuing March of Common Green Iguanas: Arrival on Mainland Asia
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Journal for Nature Conservation 57 (2020) 125888 Contents lists available at ScienceDirect Journal for Nature Conservation journal homepage: www.elsevier.com/locate/jnc The continuing march of Common Green Iguanas: arrival on mainland Asia Matthijs P. van den Burg a,*, Steven M. Van Belleghem b, Christina N. De Jesús Villanueva c,d a Department of Biogeography and Global Change, Museo Nacional de Ciencias Naturales, Spanish National Research Council (CSIC), c/ Jos´e Guti´errez Abascal 2, 28006 Madrid, Spain b Department of Biology, University of Puerto Rico, Río Piedras, San Juan, Puerto Rico c College of Environmental and Life Science. University of Rhode Island, Kingston, Rhode Island, USA d International Institute of Tropical Forestry, United States Forest Service, United States Department of Agriculture, San Juan, Puerto Rico ARTICLE INFO ABSTRACT Keywords: The popularity of the Common Green Iguana (Iguana iguana) as a pet has contributed to its global occurrence as Citizen science an invasive alien species. Early detection and control of alien I. iguana populations is necessary to prevent the Invasive alien species need for large and financially demanding eradication actions. Here, we first collated information from digital Legislation footage and interviews regarding sightings of free roaming I. iguana specimens in Singapore and Thailand. We Range expansion use this information to report and discuss an ongoing invasion with early stage establishment being facilitated by Social media Wildlife trade release of pets and escape from recreational parks, as well as the resulting conservation implications. Using species-distribution modeling to assess the potential distribution in Southeast Asia, we identify large regions with suitable habitat that could aid the expansion of these alien populations in the absence of future control measures. In addition, given the availability of suitable habitat throughout the Philippine archipelago and its high number of imported iguanas and within-country trade, we call for awareness of future alien I. iguana populations in the Philippines. Next, the alien population in Singapore is of additional concern given that the excellent swimming capacity of I. iguana allows it to reach neighboring Sumatra and > 3,000 islands of the Indonesian Riau archi pelago. Finally, we report I. iguana sightings in Hong Kong and Peninsular Malaysia. We provide strategy rec ommendations for implementing mitigation efforts and to halt future release and spread in order to prevent negative biodiversity impacts associated with a large invasive alien I. iguana population. 1. Introduction established populations of this invasive alien species (IAS) have so far not been successfully eradicated (Lee et al., 2019; Rivera-Milan´ & The Common Green Iguana (Iguana iguana, Linnaeus, 1758) is a Haakonsson, 2020), though several efforts are currently underway (e.g. heavily traded reptilian pet species that has seen its global transport Dominica and Fiji). regulated since 1977 (CITES, 2019). In fact, the pet trade is the most The rapid growth of I. iguana populations can pose a threat to the important contributor to the origin of non-native populations of green economy of invaded territories, through infrastructure damage and iguanas (Bock, Malone, Knapp, & Aparicio, 2018; Falcon,´ Ackerman, agricultural loss, as well as threats to biodiversity (Bock et al., 2018; Recart, & Daehler, 2013; Kraus, 2009), although invasions have also Falcon´ et al., 2013). As alien populations can originate from multiple been aided through over-water dispersal following hurricanes and sub genetic lineages (Stephen, Reynoso, Collett, Hasbun, & Breinholt, 2013; sequent post-hurricane relief efforts (Censky, Hodge, & Dudley, 1998; van den Burg, Meirmans et al., 2018) high genetic diversity might in van den Burg, Brisbane, & Knapp, 2020). Iguana iguana is native crease adaptive variation to persevere in non-native environments, as throughout Central and South America as well as on several Caribbean seen for other non-native lizards (e.g., Kolbe et al., 2004). It has been islands (Stephen, Reynoso, Collett, & Hasbun, 2013; Bock et al., 2018). suggested that the growth of non-native I. iguana populations is aided by Invasions of I. iguana are mainly restricted to Caribbean islands and the low number of predators and direct competitors (Lopez-Torres,´ Florida (USA), with only a small set of islands known from outside this Claudio-Hernandez,´ Rodríguez-Gomez,´ & Longo, 2011); however, this region: Fiji, Hawaii (USA), Japan (Ishigaki island), and Taiwan (Bock and other hypotheses on the growth of these populations remain un et al., 2018; Lee, Chen, Shang, & Clulow, 2019). Importantly, tested (e.g., lack of parasites, high food abundance, enemy-release * Corresponding author. E-mail address: [email protected] (M.P. den Burg). https://doi.org/10.1016/j.jnc.2020.125888 Received 2 March 2020; Received in revised form 12 August 2020; Accepted 13 August 2020 Available online 18 August 2020 1617-1381/© 2020 Elsevier GmbH. All rights reserved. M.P. den Burg et al. Journal for Nature Conservation 57 (2020) 125888 hypothesis). Furthermore, non-native I. iguana populations are a threat recreational parks) we asked whether I. iguana were kept in holding to native species through direct physical and hierarchical competition cages or were freely roaming. In the latter case, we recorded these fa and hybridization (Vuillaume, Valette, Lepais, Grandjean, & Breuil, cilities as potential sources for current and future alien populations. 2015; Moss et al., 2017; van den Burg, Breuil, & Knapp, 2018; van Wagensveld & van den Burg, 2018). On Grand Cayman, an island of 196 2.2. Suitable habitat modeling km2, the present invasive I. iguana population was estimated to reach between 0.9–1.9 million individuals in early 2018 before the start of a Species distribution modeling is generally used to identify the cli government-financed culling program (Rivera-Milan´ & Haakonsson, matic niche of a species using available climatic data retrieved from 2020). During this program’s initial year, through collective work of 500 observation record locations. This method has been broadly imple hunters, over 960,000 iguanas were removed at the expense of 5.7 mented to predict the potential distribution of both native and alien million USD (Rivera-Milan´ & Haakonsson, 2020). As the successful species (e.g. Srivastava, Griess, & Keena, 2020), as well as for future eradication of Eleutherodactylus coqui on O’ahu (Hawai’i) (Beachy, climate scenarios (Velasquez-Tibat´ a,´ Salaman, & Graham, 2013). Pre Neville, & Arnott, 2011) demonstrated, preventing further spread of IAS viously this method has also been applied to Iguana iguana (Falcon´ et al., and the need for multimillion-dollar population-reduction or eradica 2013), although elevation data – an important abiotic variable that tion programs depends on key rapid management action during the limits this species presence and distribution (Stephen et al., 2013) – introduction and establishment phases (Davis, 2009; Blackburn, Pyˇsek, were not included in the model. & Bacher, 2011). To understand the potential range of Iguana iguana in Southeast Asia, In Southeast Asia, Thailand and Singapore are considered important we used MaxEnt (Philips, Dudík, & Schapirem, 2018) as implemented in hubs in the international wildlife trade (Nijman, 2010). In these coun the dismo R package (Hijmans, Phillips, Leathwick, & Elith, 2017; R Core tries, herpetofaunal survey reports identified notable discrepancies Team, 2019) to build species distribution models (SDM), for current and among CITES import data and the presence of several non-native species future climate scenarios. Specifically, it allows us to identify the po in the wild (Nijman & Shepherd, 2007, 2010, 2011; Yeo & Chia, 2010; tential Southeast Asian range of I. iguana in the absence of mitigation Poole & Shepherd, 2017). For Thailand, Nijman and Shepherd (2011) actions and identify those areas where viable populations are most likely found that over 150 distinct non-native species of amphibians and rep to occur. MaxEnt uses environmental and climatic data from tiles had CITES import records between 1990–2007. In contrast, only species-occurrence localities to build a predictive SDM of habitat suit two alien reptile species (Trachemys scripta elegans and I. iguana) were ability (HS) for the study species, which runs between 0 (low suitability) recorded in Thailand during a 2011–2012 inventory of wild alien and 1 (high suitability). vertebrate fauna (Boonkuaw, Kanchanasaka, & Prayoon, 2014). For We acquired I. iguana occurrence data uploaded to the Global I. iguana, Boonkuaw et al. (2014) reported three sightings of single Biodiversity Information Facility (GBIF.org, 2019), and observations of specimens in Thailand, all of which had disappeared before the report’s free-roaming iguanas from Thailand and Singapore through iNaturalist. publication. Singapore is mainly regarded as an import and re-export We retained occurrence data from established alien populations where country (Nijman, Todd, & Shepherd, 2012) and was the main regional breeding occurs, arguing that, although non-native areas can hold reptile importer between 1998–2007 (Nijman, 2010). In contrast to different climatic compositions compared to native areas, local climatic Thailand, over 20 alien reptile species were present in Singapore in 2010 variables are suitable for successful reproduction and thus help to (Ng & Lim,