gecko

The Common House Gecko (Hemidactylus frenatus) is recently being reported from multiple islands across the Lesser Antilles: Antigua, Dominica, St. Barthélemy, St. Eustatius, St. Kitts, St. Lucia, and St. Martin (Brisbane et al. 2021, Dewynter et al. 2022, Griffing et al. 2022, Thorpe 2022, Questel et al. 2023, Thibaudier et al. 2023, Lindsay et al. 2023). Here, we report on the establishment of the species on Saba, Dutch Caribbean.

On 27 November 2023, between 19.30–20.30 h, we surveyed buildings, walls, rock crevices and piles of wood, brick, concrete, and metal, including building supplies, on the Fort-Bay Road, adjacent to the Fort Bay harbor on Saba (17.61615, -63.25039). We found H. frenatus at eight locations along a 520-meter stretch of road, either on walls, next to the road between rocks, or between aforementioned materials. At each location one animal was captured, totaling four adults and four juveniles. The lamellae on the 4th and 5th digit were used to confirm species identity (Krysko and Daniels 2005). We collected one adult (Figure 1) that has been provided to Naturalis Biodiversity Center, Leiden, The Netherlands, for deposition in their collections. We note that Hemidactylus mabouia was also found at three sites within the 520-meter stretch, but never closer than ~30 meters to Hemidactylus frenatus, which is a known competitor of other gecko species (Petren & Case 1996).

ABSTRACT

A major challenge in invasion ecology is determining which introduced species pose a threat to resident species through competitive displacement. Here, we provide a statistical framework rooted in coexistence theory to calculate coexistence outcomes – including competitive displacement – between resident and invading species. Advantageously, our framework uses readily available trait and abundance data rather than the demographic data traditionally used in coexistence theory applications which is often difficult to collect for most species. Our framework provides methods for predicting displacement that has yet to manifest in incipient invasions, and for quantifying displacement in ongoing invasions. We apply this framework to the native and introduced gecko species on Curaçao and predict the displacement of all three native species by introduced species and quantify that the displacement of one native species is already underway. Our results affirm that trait and abundance data are suitable proxies to reasonably predict and quantify coexistence outcomes. 

Introduction

The Caribbean region is emerging as a hotspot for the spread of non-native reptile species (Powell et al. 2011; Powell and Henderson 2012). Two lizard groups, anoles (species from the genus Anolis) and geckos (species from the infraorder Gekkota), are among the most prominent of introduced reptiles on Caribbean islands (Helmus et al. 2014; Perella and Behm 2020). Anole and gecko species are frequently introduced accidentally through the live plant trade, but may also be introduced intentionally as pets (Kraus 2009). The Caribbean region is also a reptile biodiversity hotspot and most islands have unique endemic anole and gecko species (Myers et al. 2000; Hedges 2011). Therefore, identifying newly introduced gecko and anole species, including their introduction pathways and ecological impacts, is a conservation priority.

Aruba has 10 previously recorded introductions of non-native reptile species, including two anoles, Anolis sagrei (Duméril & Bibron, 1837) and A. porcatus (Gray, 1840), and four geckos, Gonatodes albogularis (Duméril & Bibron, 1836), G. antillensis (Lidth de Jeude, 1887), G. vittatus (Lichtenstein & Martens, 1856), and Hemidactylus mabouia (Moreau de Jonnès 1818), making it one of the most invaded islands in the Caribbean (van Buurt 2005, 2011). Aruba is also one of the most economically connected islands in the region which likely explains the high rate of introductions (Powell et al. 2011; Helmus et al. 2014). Interestingly, unlike most Caribbean islands, the natural habitat in Aruba is quite arid and may be difficult for species to invade if they are not adapted to those conditions. Many of the non-native species may be using anthropogenic habitat that receives irrigation subsidies. Given the high rate of introductions and harsh natural conditions, we searched anthropogenic habitat on Aruba for non-native reptile species. Here, we report the first observations of two new non-native anole and one non-native gecko species on Aruba. In addition, we report a range expansion of a non-native anole species that was previously observed at only one location on Aruba. To better understand the context and potential impacts of the four introduced species we documented on Aruba, we compiled information from the literature regarding the timing, introduction pathway, and ecological impacts of those four species in their introduced ranges within the Caribbean region.

Abstract

The Caribbean islands are becoming a hotspot for the spread of non-native reptiles. Consistent with this trend, we provide the first documentation of three new lizard species discovered on Aruba, Anolis gingivinus (Cope, 1864), Anolis cristatellus (Duméril and Bibron, 1837), and Hemidactylus frenatus (Duméril and Bibron, 1836). In addition, we provide an updated distribution on Aruba for a previously introduced lizard species, Anolis porcatus (Gray, 1840). All four species were identified phenotypically in the field and identifications were confirmed with genetics. Like most non-native lizards in the Caribbean, they tend to use anthropogenic habitats, and their impacts on Aruba’s resident species are not known.

House geckos in the genus Hemidactylus are highly successful colonizers of regions beyond their native range, with colonization often resulting in displacement of native gecko species through competitive interactions for daytime refuge (crevices) and prey resources. We report on data collected from nighttime surveys undertaken in April-May 2014 on Barbados, West Indies, that focused on the distribution and abundance of the endemic Barbados leaf-toed gecko (Phyllodactylus pulcher) and the introduced tropical house gecko (Hemidactylus mabouia) along unlit coastal walls and among boulders in the grounds of a hotel resort. In contrast to patterns of displacement of native species by H. mabouia seen elsewhere, P. pulcher was more abundant than H. mabouia on coastal walls, whereas the latter was found in greater numbers using boulders at this site. Walls and boulders differed with regard to availability of diurnal refugia suitable for geckos, with the walls having high frequency of small crevices with openings <20 mm, and boulders offering very little cover other than the underside of the boulder itself. To investigate whether this niche separation was a result of differences in diurnal refuge use between the species, we conducted experimental trials in which geckos were allowed to select between refugia with different characteristics. Both species selected for narrower and warmer refugia, and refugia that had been previously occupied by the other species. These shared preferences for refugia type suggest that other factors underlie the niche separation observed in the field. In supporting high densities of P. pulcher, coastal walls could offer important secondary habitat by augmenting the natural cliff side habitat of this endemic gecko, a finding that could be exploited for the conservation of this candidate species for Critically Endangered classification.

ABSTRACT

We used nightly surveys to monitor the status of building-dwelling gecko species on the southern Caribbean island, Curac ̧ ao. Two gecko species were detected in 10 counts across five nights from 18 sites. We recorded the nonnative Wood Slave, Hemidactylus mabouia (81%, 369/455 observations), native Dutch Leaf-Toed Gecko, Phyllodactylus martini (11%, 50/455 observations), and unidentified geckos (8%, 36/455 observations) on the island. The Dutch Leaf-Toed Gecko was most common near the forest and rare elsewhere. Wood Slave abundance was not influenced by forest proximity. Wood Slaves commonly perched near lights that provided heat and attracted insect prey. In contrast, the Dutch Leaf-Toed Gecko perched away from lights. Similar to gecko species in Florida, Wood Slaves displaced Dutch Leaf-Toed Geckos. The Dutch Leaf-Toed Gecko was syntopic with the Wood Slave on buildings near the forest when resources were not limiting or if other gecko populations were not self-sustaining. As Wood Slave populations grew, they excluded Dutch Leaf-Toed Geckos, and possibly Antilles Geckos, Gonatodes antillensis, from these buildings. This exclusion adds novel obstacles to the continued survival of the Dutch Leaf-Toed Gecko on Curac ̧ ao. A similar situation may be present on Bonaire, and for a congeneric species on Aruba, where the Wood Slave is a more-recent colonist.