Disentangling the Influence of Urbanization and Invasion on Endemic Geckos in Tropical Biodiversity Hot Spots: A Case Study ofPhyllodactylus martini(Squamata: Phyllodactylidae) along an Urban Gradient in Curaçao

Abstract

Predicting the response of endemic species to urbanization has emerged as a fundamental challenge in 21st century conservation biology. The factors that underlie population declines of reptiles are particularly nebulous, as these are often the least understood class of vertebrates in a given community. In this study, we assess correlations between feeding ecology and phenotypic traits of the Lesser Antillean endemic Dutch leaf-toed gecko, Phyllodactylus martini, along an urban gradient in the Caribbean island of Curaçao. There has been a marked decline of this species in developed habitats associated with the invasive tropical house gecko Hemidactylus mabouia. We find a correlation between aspects of locomotor morphology and prey in undeveloped habitats that is absent in developed habitats. Analyses of stomach contents further suggest that Phyllodactylus martini alters primary prey items in developed areas. However, changes in prey promote the overlap in foraging niches between Phyllodactylus martini and Hemidactylus mabouia, suggesting that direct resource competition is contributing to the decline of Phyllodactylus martini. In addition to competitive exclusion, we suggest that the urban extirpation of Phyllodactylus martini could also be attributed to a top-down control on population growth by Hemidactylus mabouia. Colonizations of walls put Phyllodactylus martini in direct contact with Hemidactylus mabouia increasing the chances for predation events, as evidenced by our observation of a predation event on a Phyllodactylus martini juvenile by an adult Hemidactylus mabuoia. In total, our results add to a growing body of literature demonstrating the threat that invasive synanthropic reptiles pose to endemics that might otherwise be able to cope with increased urbanization pressures.

Comparing the dietary niche overlap and ecomorphological differences between invasive Hemidactylus mabouia geckos and a native gecko competitor

“…We conducted a principal components analysis (PCA) to visualize the overall morphospace occupied by both species. In geckos, size has been shown to covary with our target morphological measurements (Dornburg et al, 2016). To account for this, we first regressed all the measurements per species against log-transformed SVL and used the residual values of individual traits regressed against log-transformed SVL as data for the PCA.…”

“…While this suggests competition to be an important aspect of H. mabouia invasions, dietary niche overlap with native species is often not known, and other hypotheses concerning possible ecological advantages over native species remain little explored. For example, the feeding mode of H. mabouia combines ambush tactics (Vitt, 1983) with active pursuit of nearby prey (Dornburg et al, 2016). Such a foraging mode could have been selective for larger hind limb or shorter fore-limb proportions that, respectively, offer a locomotor advantage over native species when accelerating or decelerating on sheer vertical surfaces common in urbanizing landscapes (Zaaf & Van Damme, 2001).…”

“…Similar to H. mabouia, P. martini readily colonizes walls and takes advantage of insect and arachnid prey drawn to artificial lights (Dornburg et al, 2016;van Buurt, 2004). Although P. martini is predicted to fare well in suburban conditions (Dornburg et al, 2016;van Buurt, 2004), established populations have been rapidly declining following the introduction of H. mabouia in the 1980s (Dornburg et al, 2016;Hughes et al, 2015;van Buurt, 2004van Buurt, , 2006. This decline has been attributed to H. mabouia possessing a superior competitive ability based primarily on behavioral observations (Hughes et al, 2015), with no quantification of dietary overlap between these species.…”

Terrestrial Vertebrate Invasions in South Africa

“…Populations of H. mabouia species have invaded West Africa, the Caribbean, South America and Florida (Weterings and Vetter 2018). Invasions have resulted in displacement of native geckos in Florida and Curaçao (Dornburg et al 2016;Short and Petren 2012, but see also Williams et al 2016). The first extralimital records in South Africa for this species are for East London and Port Elizabeth in the 1980s (Brooke et al 1986;Rebelo et al 2019), although, like the common dwarf gecko (see below), first sightings in Port Elizabeth may be biased to the activities of a keen resident herpetologist and the true dates for other cities may be earlier than reported.…”

What makes Hemidactylus invasions successful? A case study on the island of Curaçao

“…feeding mode of H. mabouia combines ambush tactics (Vitt 1983) with active pursuit of nearby prey 111 (Dornburg et al 2016). Such a foraging mode could have selected for limb proportions that offer a 112 mechanical advantage on sheer vertical surfaces (Zaaf and Van Damme 2001 ordination represents a viable indicator of species dissimilarity, with stress values less than 0.1 indicating 201 good representation of the dissimilarities (Clarke 1993).…”