Invasive rodents, an overlooked threat for skinks in a tropical island hotspot of biodiversity

Abstract

Squamata are one of the most threatened groups among island vertebrates, facing high pressure from exotic species. However, the contribution of small terrestrial reptiles in invasive rodents' diet remains poorly investigated, partly because of the lack of tools for accurately identifying chewed prey fragments in gut contents. The New Caledonia archipelago (South Pacific) hosts an exceptional terrestrial squamata fauna (105 species, 91.6% endemic) that are faced with many invasive species (rodents, feral cats, feral pigs, ants) and strong human pressures. Our study aimed to evaluate the frequency of occurrence of endemic skink remains by gut content analysis of two species of invasive rodents. Four rodent trapping sessions were implemented at two ultramafic sites and for two distinct habitats (closed canopy forest and open shrubland habitat). A total of 284 rats were trapped from two species (the ship rat Rattus rattus and the Pacific rat R. exulans) over 1200 trap nights. Combined analysis of stomach and caecum contents provided far more information than traditional stomach analysis alone. Analyses showed that 15.9% of rat samples included remains of at least 12 different skink species out of the 23 present. Six species are classified as threatened by the IUCN, the most endangered being Marmorosphax taom (CR) and Kanakysaurus viviparus (EN). This study provides new prospects for the assessment of invasive rodent impacts and new insights into the respective impacts of two sympatric invasive rodent species on native skinks.

Ship rats and island reptiles: patterns of co-existence in the Mediterranean

“…The ship rat is also an efficient colonizer of small islets, and once it reaches an archipelago, there is frequent inter-island dispersal (Cheylan, Granjon & -Davidian, 1998). Both its diet and dispersal capacity induced historical pernicious effects on island reptiles, particularly on isolated oceanic islands (Thibault et al, 2017).…”

Sympatric Invasive Rats Show Different Diets in a Tropical Rainforest of an Island Biodiversity Hotspot1

“…Although the management of invasive species in New Caledonia is of primary importance in order to preserve its native and endemic biodiversity (Beauvais et al, 2006, Pascal et al 2008, very few studies have been conducted on New Caledonia's rat population ecology and diet (Robinet et al 1998, Rouys 2008, Brescia 2011, Thibault et al 2017). Our study shows that both Rattus spp.…”

“…For both rat species, diets were assessed by morphological analysis of food items from stomach and caecum contents. Although the majority of diet studies are based on stomach contents alone (Sugihara 1997), a recent study has shown that combined analysis of stomach and caecum contents provides much more information on taxon richness in rat diet, particularly for Squamata (Thibault et al 2017). Each sample, that is, stomach or caecum, was rinsed with tap water and sieved through a 500 mm mesh (Sugihara 1997).…”

“…Therefore, we chose to estimate frequencies of occurrence and volume scores based on stomach contents data only. By contrast, we used both stomach and caecum data in order to get the maximum resolution on Squamata diversity in rat diet (Thibault et al 2017).…”

Kuniesaurus albiauris, a New Genus and Species of Scincid Lizard from the Île des Pins, New Caledonia, with Comments on the Diversity and Affinities of the Region's Lizard Fauna

“…come from the presence of invasive species, primarily rodents (Pacific Rat and Ship Rat), feral cats, and invasive ants. The negative impact of rats on island lizard populations has been well documented (Whitaker 1973;Monks et al 2014), with their presence clearly suppressing potential lizard population densities (Thibault et al 2017). A negative impact on lizard populations by the Little Red Fire Ant (LFA) Wasmannia auropunctata has also been identified, with studies in dry forest habitat in New Caledonia reporting a lower abundance of several lizard species in invaded areas (Jourdan et al 2001), and it is considered to be a major threat islandwide.…”