Cryptic extinction risk in a western Pacific lizard radiation

Abstract

Cryptic ecologies, the Wallacean Shortfall of undocumented species' geographical ranges and the Linnaean Shortfall of undescribed diversity, are all major barriers to conservation assessment. When these factors overlap with drivers of extinction risk, such as insular distributions, the number of threatened species in a region or clade may be underestimated, a situation we term 'cryptic extinction risk'. The genus Lepidodactylus is a diverse radiation of insular and arboreal geckos that occurs across the western Pacific. Previous work on Lepidodactylus showed evidence of evolutionary displacement around continental fringes, suggesting an inherent vulnerability to extinction from factors such as competition and predation. We sought to (1) comprehensively review status and threats, (2) estimate the number of undescribed species, and (3) estimate extinction risk in data deficient and candidate species, in Lepidodactylus. From our updated IUCN Red List assessment, 60% of the 58 recognized species are threatened (n = 15) or Data Deficient (n = 21), which is higher than reported for most other lizard groups. Species from the smaller and isolated Pacific islands are of greatest conservation concern, with most either threatened or Data Deficient, and all particularly vulnerable to invasive species. We estimated 32 undescribed candidate species and linear modelling predicted that an additional 18 species, among these and the data deficient species, are threatened with extinction. Focusing efforts to resolve the taxonomy and conservation status of key taxa, especially on small islands in the Pacific, is a high priority for conserving this remarkably diverse, yet poorly understood, lizard fauna. Our data highlight how cryptic ecologies and cryptic diversity combine and lead to significant underestimation of extinction risk.

Supplementary information: The online version contains supplementary material available at 10.1007/s10531-022-02412-x.

Keywords: Geckos; IUCN red list; Lepidodactylus; Linnean shortfall; New Guinea; Philippines; Wallacea.

Fig. 1

Examples of Lepidodactylus: a the newly described Lepidodactylus bisakol from the southern Bicol Peninsula, Philippines (Jason Fernandez and Rafe Brown); b the newly described Pseudogekko hungkag from Luzon Island, Philippines (Jason Fernandez and Rafe Brown); c an undescribed Lepidodactylus species from the Bismark Islands, Papua New Guinea (Steven Richards); and d Lepidodactylus flaviocularis known from only two specimens at one location on Guadalcanal, Solomon Islands (Scott Travers)

Fig. 2

a Distribution of described Lepidodactylus species (black dots represent location records; www.gbif.org) across regions of the tropical western Pacific (excluding the widespread anthropogenically dispersed species L. lugubris). b Status of described Lepidodactylus species (n = 58) by region (DD data deficient, LC least concern, NT near threatened, VU vulnerable, EN endangered, CR critically endangered, EX Extinct)

Fig. 3

Distribution of key threats nominated to described Lepidodactylus species across regions of the tropical western Pacific, including numbers of species affected by each threat. Note that not all species have listed threats and some species have multiple threats, thus total numbers across threat categories will not match the number of species in each region

Fig. 4

Numbers of described and candidate Lepidodactylus species by region (indicated above each column) and threat status (colours; see key below) in the tropical western Pacific. ‘Threatened’ (VU, EN, CR) and ‘Other’ (DD, LC, NT) candidate species were assigned based on our logistic regression model