Amphibian and reptile diversity along a ridge-to-reef elevational gradient on a small isolated oceanic island of the central Philippines ANNOTATED LIST OF SPECIES

Despite multiple recent field studies, herpetological species diversity of the Romblon Island Group in the central Phil ippines—particularly Sibuyan Island—has remained underestimated. Recently, we investigated the diversity of the herpetofauna of Mount Guiting-Guiting Natural Park, based on an elevational transect (10–1557 m a.s.l.). Our surveys resulted in a total of 47 species of amphibians and reptiles, including 14 new island records and one atypical occurrence of a snake species recorded for the first time from a high elevation (939 m a.s.l). These new records constitute a notable increase (21%) in Sibuyan’s herpetological species diversity as compared to surveys from a decade ago. We also provide updates of the taxonomy and identification of species endemic to this island (e.g., members of the genera Platymantis Günther, 1858, Brachymeles Duméril & Gibron, 1839, and Pseudogekko Taylor, 1922), and discuss the importance of continued surveys and field-derived data to inform conservation status assessments of Sibuyan’s unique assemblage of amphibians and reptiles.


Introduction
The Philippine archipelago comprises over 7100 islands strewn over the Western Pacific Ocean (Goodman et al. 1995;Heaney and Regalado 1998;Heaney et al. 2005). The partitioned nature of the archipelago has contributed to the evolution of many unique and range-restricted life forms , and the country is now believed to harbor the greatest diversity of land vertebrate species per unit land area on earth Myers et al. 2000).
Our understanding of Philippine terrestrial vertebrate biodiversity has improved significantly over the past few decades Diesmos et al. 2015;Leviton et al. 2018). Extensive field surveys, coupled with major advances in analyses of available data have demonstrated that the Philippine fauna is far richer-with proportionally higher endemism and with more variable and complex evolutionary and biogeographic histories-than previously assumed Brown and Guttman 2002;Diesmos et al. 2002b). Of the 1196 native species of amphibians, birds, mammals, and reptiles currently known to occur in the country, nearly 46% are endemic, with many more island endemics continually being discovered Evans et al. 2003;Heaney and Regalado 1998;McGuire and Heang 2001;Peterson et al. 2008). Much of this shift in appreciation of evolutionary diversification in the archipelago has resulted from an increased understanding of the complex geological history of the archipelago (Hall 1998;Yumul et al. 2009), which is believed to have played a major factor in the evolution of the Philippines' soaring levels of terrestrial vertebrate diversity (Heaney 1986(Heaney , 1998(Heaney , 2000Brown et al. 2013a). Centers of endemism in the archipelago are coincident with the physiography of the greater Pleistocene Aggregate Islands Complexes (PAICs) of Luzon, Palawan, Negros-Panay (West Visayan islands), Mindoro, Mindanao, and the Sulu Archipelago during Pliocene and Pleistocene sea level regressions (Inger 1954;Voris 2000). However, until relatively recently, little attention has been paid to fully inventorying smaller islands like those in central Romblon Province.
The Romblon Island Group (RIG; Fig. 1) is approximately 350 km south of Manila and is situated in the Sibuyan Sea, south of Marinduque Island and north of Panay Island. East of the RIG is the island of Masbate; to the island group's west is the large Mindoro Island (Fig. 1). Aside from being renowned for its lush vegetation and mineral resources, the RIG is also known for its diverse offshore fisheries, where migration paths of many marine species from the Sulu and Visayan seas pass the Tablas Strait, Sibuyan Sea, and Romblon Pass (Carpenter and Springer 2005;Han et al. 2009;Leyzack et al. 2014). Hence, not only the landscapes but also the seascapes of the RIG are rich in biodiversity and possibly in need of wholesale faunistic studies and conservation management (DENR-PAWB 2009;Clemente et al. 2017).
Owing to the central position of the RIG and its geologic significance in the context of the Philippines' geologically dynamic arc-continent collision system ), the small islands of the RIG are of keen interest to geologists and biogeographers Alcala 1970, 1974;Goodman and Ingle 1993;Esselstyn and Goodman 2010;Siler et al. 2012). Romblon Province is composed of three major islands: Tablas has a land area of 668 km 2 , making it the largest; Sibuyan is the second largest (449 km 2 ); and Romblon Island proper is the smallest, with a land area of just 82 km 2 . The channel between Romblon and Tablas is less than 50 m deep and, thus, the two islands were likely connected by a Pleistocene land bridge at their northern ends (Allen 2006;Brown et al. 2011a;Siler et al. 2012); however these islands are separated from Sibuyan Island by water more than 500 m deep (Gordon et al. 2011), suggesting that the latter remained isolated during the entirety of the Pleistocene. The RIG's complex, mobile geologic history resulted from various crustal plate movements, spreading rift zones, and subduction-all of which could have contributed to the island group's terrestrial vertebrate biodiversity (Yumul et al. 2003Siler et al. 2012). Additionally, over the most recent millennia (Pleistocene: 2.5 million years ago), none of the landmasses of Romblon Province, including Sibuyan Island have been connected by dry land to the larger, surrounding landmasses of the Luzon, Mindoro, or West Visayan PAICs Diesmos 2002, 2009;Fig. 1).
On Sibuyan Island lies a prominent massif, called Mount Guiting-Guiting ( Fig. 1), which is central to Mount Guiting-Guiting Natural Park. Together with its forests, it is recognized as a key biodiversity area (Ingle 1993;Goodman et al. 1995;Rickart et al. 2005;Siler et al. 2012) and is noted as one of only a few remaining mountains in the Philippines with relatively intact habitats from sea level to its peak (Goodman and Ingle 1993;Tongson and McShane 2006;Siler et al. 2016 ). The mountain spans 45,600 ha, and roughly 70% is covered with forest along its entire elevational gradient relief (Tongson and McShane 2006). The Philippines' National Integrated Protected Areas Program (NIPAP) reported several distinct habitats types (vegetation zones) as: summit heathland and grasslands, mossy forests, montane forests, lowland evergreen forest, and forest over ultrabasic rocks (Goodman et al. 1995). This environmental and habitat diversity supports rich biodiversity that contributes to global recognition of the Philippines as a megadiverse, global conservation hotspot country (Myers et al. 2000;Von Rintelen et al. 2017). This fact warrants continued research and conservation effort focused on Mount Guiting-Guiting Natural Park.
Throughout the past three decades, the rich biodiversity of this protected area has been characterized, and new species discovered, by focusing on Mount Guiting-Guiting itself, which has bolstered the case for its extremely high conservation value (Esselstyn and Goodman 2010;Brown et al. 2011a;Siler et al. 2012Siler et al. , 2016. However, even as scientific research continues to highlight the protected area's rich natural resources, the mountain's rugged terrain and inaccessibility, together with limitations in resources for prolonged research, has resulted in the paradoxical situation in which the actual forests on the mountain itself have not been extensively studied. With rapidly expanding agricultural croplands, illegal logging, and human settlements (Goodman and Ingle 1993;Goodman et al. 1995;Esselstyn and Goodman 2010;Siler et al. 2016), a continuous degradation of Mount Guiting-Guiting's landscape, and potential loss of biodiversity and ecosystem services have contributed to recent estimates of nearly 30% of its original forests suffering some form of degradation (Heaney and Regalado 1998). As a consequence, an empirically documented understanding of Mount Guiting-Guiting's current environmental status has now become imperative. This spatial, elevational, and taxonomic analysis of biodiversity can serve as a resource to determine the status of the protected areas (Allen 2006;Davis et al. 2016).
Among the established indicators of environmental health are amphibians and reptiles which differentiate on a fine scale with environmental, elevational, and geographic history variation (Brown and Alcala 1961;Inger 1980;Lieberman 1986;Blackburn et al. 2013;Wollenberg-Valero et al. 2019). Alcala (1986) emphasized that proper management, conservation, and preservation of the natural resources of the Philippines depends on the availability of comprehensive and up-to-date biodiversity inventory information. Thus, updated and augmented information generated in this study will serve as a critical baseline for future amphibian and reptile ecological and systematic studies, and should prove significant for the assessment of conservation status of terrestrial fauna of the Mount Guiting-Guiting Natural Park Protected Area (Diesmos et al. 2014(Diesmos et al. , 2015Leviton et al. 2018).
Sibuyan was identified for this study as a focal site for research because of its unique complex ecosystem with notable geologic history that contributed with its high endemism-oceanic origin, geographic isolation, elevational relief, and relatively intact forests. In addition, Sibuyan Island presents biogeographically compelling questions relating to the colonization history of organisms that could only have arrived on Sibuyan by dispersing over water (Goodman and Ingle 1993;Siler et al. 2012). We also initiated the present study under the premise that a comprehensive characterization of the diversity and distribution of amphibians and reptiles of Mount Guiting-Guiting would be highly desirable on the part of the local government, specifically the Protected Management Board and the regional Department of Environment and Natural Resources (Region IV-B) for future management planning. The additional information and data will strengthen their existing conservation programs ideally by engaging local communities, wildlife managers, ecotourists, and university researchers in Romblon Province.
Here, we provide a comprehensive report of characterizing amphibian and reptile records for Mount Guiting-Guiting Natural Park and provide comparisons with previous faunal summaries of Romblon Province. We also follow suggestions of Siler et al. (2012) and emulate Goodman et al. (1995) in discussing biogeographical and evolutionary affinities of Sibuyan's endemic taxa. The study presents an up-to-date list with new island records of the diversity of amphibians and reptiles, which suggests the necessity and significance of periodic, repetitive surveys, and to revisit and augment the findings of previous studies in protected areas and other sites of high-value conservation importance.

Study Area
Sibuyan Island is the second largest island of Romblon Province; it is a small, geologically young island which is approximately six millions years old (Hall and Holloway 1998), surrounded by diverse source pools of potential vertebrate colonist from islands of Leyte, Luzon, Mindoro, and Panay (Esselstyn and Goodman 2010;Fig. 1). Sibuyan Island has not been connected to any other island throughout its geological history because it is oceanic in origin (Hall 1998;Heaney 1986;Inger 1954;Voris 2000). It measures 28 km from east to west and 24 km from north to south. The island is located at 12°24′, 122°33′E and has a total land area of approximately 44,500 ha.
At Sibuyan's heart is Mount Guiting-Guiting Natural Park (MGGNP), which is bounded on the north by the Municipality of Magdiwang. Mount Guiting-Guiting is a steep mountain with jagged topography ( Fig. 2A), standing 2058 m above sea level (a.s.l.); it is considered to be one of only a few remaining mountains in the archipelago with intact, forested habitats that covers an area of 10,000-15,000 ha out of Sibuyan's total area of 44,500 ha (comprising different vegetation types and floral communities) along its entire elevational gradient from sea level to its peak (Goodman et al. 1995;Goodman and Ingle 1993;Tongson and McShane 2006;Fig. 2). Mount Guiting-Guiting is formed by intrusive Sibuyan island ultramafic geology (Proctor et al. 1997;Yumul et al. 2003Yumul et al. , 2005Yumul et al. , 2008, and vegetational zonation associated with ultramafic rocks has been described as unusually distinctive and highly variable Payot et al. 2009;Yumul et al. 2009).
Fieldwork was conducted along the primary elevational gradient composing Mount Guiting-Guiting Natural Park. Our surveys were conducted at five major sites, and involved two separate seasonal sampling efforts. Locations 1-5 were surveyed 23 October-23 November 2016 and 24 May-25 June 2017 (six days exhaustive sampling per elevational base-camp increment), corresponding to the onset of the monsoon season, and then also to the final months of the dry season, respectively. Basecamp sampling sites were chosen with reference to the altitudinal gradient study of Goodman et al. (1995). Survey areas included the lowland evergreen forest, montane forest, mossy forest, coastal areas, and agricultural areas distributed throughout varying elevations between 10 and 1557 m a.s.l. (Fig. 1). The actual summit (>1600 m a.s.l.) was excluded in the sampling due to the limitation of financial resources, difficulty of the trail, time constraints, and extreme weather conditions.
Below is the summary of the ranges of elevation that were surveyed in different location sites.
Location 1: 10-148 m a.s.l. (12°28′53″N, 122°33′ 01″E). The site was characterized by secondary-growth forest mixed with private agricultural lands, and coastal mangrove forest stands. Several small to medium-sized streams and large rivers are found in the area (e.g., Lambingan Fall, Gaong River, Jao-asan River, and the Tampayan Dam). Location 1 was commonly characterized with frequently densely overhanging rocky streams, with habitat features such as rotten logs, tall grass, dipterocarp trees, swampy areas, cultivated rice paddies, and coconut palm and mango plantations.
Location 2: 213-405 m a.s.l. (12°27′17″N, 122°32′ 40″E). This area is characterized by its steeply sloping terrain and is composed of branching tributaries leading to the Gaong River and others leading to Barangay Tampayan. Common trees belong to the families Dipterocarpaceae, Lauraceae, and Anacardiaceae, with emergent trees reaching maximum heights of 30-40 m. Epiphytic plants include mostly Araceae, Pandanaceae, and ferns. Formerly intact lowland dipterocarp forest, logging activities have reduced climax forest to a few remnant patches (Fig. 2C,D), and illegal logging and hunting continue to the present (CGM pers. observ.).
Location 5: 1500-1557 m a.s.l. (12°25′45″N, 122°33′ 26″E). Our Location 5 is mossy forest, with evidently stunted (2.5-3.0 m tall) trees, covered with thick moss and lichens (Fig. 2H), and the forest understory is densely covered by an unidentified species of Pandanus. Exposed ultramafic rocks are abundant and an expanse of heathland was present and separated from patches of mossy forest.

Methods
Fieldwork was conducted under Wildlife Gratuitous Permit to Collect No. MIMAROPA-2017-0005. We employed a combination of time-constrained searches, focused microhabitat sampling, drift-fencing and pitfall trapping, and bioacoustical-auditory surveys (Alcala et al. 2004;Heyer et al. 1994). Opportunistic sampling technique was carried out in steep terrains across the full range of altitudes and habitats, with the intent of increased sampling of behaviorally cryptic and/or patchily distributed species. Purposive sampling was performed by five persons during both daytime (6:00-8:00 hr, 10:00-11:00 hr, and 16:00-17:00 hr) and night-time (18:00-23:00 hr) hours, at all sites. Sampling hours were modified depending on weather conditions and logistical constraints. Exhaustive searches of all microhabitats were performed at the most accessible sites per elevational increment; these included rotting vegetation and logs in contact with the forest floor, tree stumps, leaf litter, leaf axils of Pandanus, rock crevices, tree trunks, bark crevices, riparian habitats, tree holes, forest trails, and clearings. To avoid disturbance, sampling sites visited during daytime were adjacent to, but different from those targeted at night. Subsequently, rotational sampling was employed, to ensure sampling of all areas and microhabitats at different times. A total of approximately 300 person-hours (60 hours/person) of time-constrained efforts were accumulated throughout this study.
We recorded the heaviest precipitation during the period of October-November 2016 with an average of 288.0 mm, coinciding with two typhoons brought by the southwest monsoon (mean temperatures from 17.7-18.9 °C; 97.8-100% relative humidity): daily intermittent rain from one full day at 1121-1551 m a.s.l. On the other hand, we recorded an average of 15.0 mm precipitation during May-June 2017 (mean temperatures from 25.5-27 °C; 76.2-100% relative humidity).
Specimens were collected, euthanized with chloretone, dissected for tissue samples (liver preserved in 100% ethanol), fixed in 10% buffered formalin, and eventually (<2 months) transferred to 70% ethanol for long-term storage (Heyer et al. 1994;Simmons 2015). New specimens contributing to this report are deposited in University of the Philippines Los Baños Museum of Natural History (UPLB-MNH), College, Los Baños, Laguna, Philippines.
Following Siler et al. (2012), we considered Sibuyan's nearest surrounding potential colonization sources (major islands or PAICs) and calculated Simpson similarity indices (S) using the formula S = C / N, where C is the number of species common to both Sibuyan and the respective source landmass, and N, is the number of species on the island of interest (Cheatham and Lazell 1969). This index summarizes the degree of faunal similarity with surrounding PAICs, assuming correct taxonomy. Regression analyses were performed, using PAST v. 3 (Hammer et al. 2001) to explore species diversity as a function of increasing topographical relief, along our focal elevational gradient.

Results
We provide documentation of 47 species of amphibians and reptiles, including 11 anurans, 21 lizards, 14 snakes, and one freshwater turtle (Table 1). Fifteen new amphibian and reptile distribution records for Mount Guiting-Guiting were recorded in the Municipality of Magdiwang (i.e., excluding the Municipalities of San Fernando, Cajidiocan, and small offshore islands; refer to Siler et al. [2012] for records from the aforementioned localities). The calculated Simpson similarity indices support significant contributions from the Luzon, West Visayan, and Mindoro PAICs as biogeographical source populations for Sibuyan's herpetofauna (Tables 2, Table 3). Of the 15 new species distributional and elevational records, 10 are associated with unresolved taxonomic uncertainty; these will require future consideration (Table 4) before identifications are fully confirmed. These include frogs of the genera Platymantis and Kaloula; lizards of the genera Gonocephalus, Lepidodactylus, Lupero saurus, Parvoscincus, and Pinoyscincus; and snakes of Table 1. Updated checklist of shared terrestrial herpetofauna along elevation gradient of Mount Guiting-Guiting Natural Park, Magdiwang, Sibuyan Island between Luzon, Mindoro, and Visayan Pleistocene Aggregate Island Complexes (PAIC:  and the islands of the RIG, compiled on the basis of Siler et al. (2012) and Supsup et al. (2016).

Class Reptilia
Order Testudines

Family Scincidae
Brachymeles dalawangdaliri x x x

Family Varanidae
Varanus nuchalis x x x

Lepidodactylus christiani
Phenotypic similarity Exhibits a tail structure and pattern not observed in Panay endemic species Brown et al. 2013a;Eliades et al. 2021;Ota et al. 1995 6. Luperosaurus sp.

Luperosaurus corfieldi
Phenotypic similarity in terms of built and size Morphological structure such as eye color, superciliaries, and body pattern are in between L. cumingii (Luzon) and L. corfieldi Brown et al. 2011a;Gaulke et al. 2007 7. Pinoyscincus sp. (P. coxi divergens complex)

Pinoyscincus coxi divergens
Black markings on the chin and elongated tail Tail longer than its body and skinks are very complex species that needs additional inspection and genotyping for definite identification Brown and Alcala 1980;Linkem et al. 2010b 8. Parvoscincus sp. (P. decipiens complex)

Parvoscincus decipiens
Color pattern similarity Skinks are very complex species that needs additional inspection and genotyping for definite identification  9. Pinoyscincus cf. jagori

Pinoyscincus jagori grandis
Phenotypic similarity Skinks are very complex species that needs additional inspection and genotyping for definite identification Linkem et al. 2010b 10. Pseudorabdion sp.

Pseudorabdion talonuran
Elevational and close phenotypic similarity (large size) Close comparison of its other morphological data is in between P. mcnamarae and P. talonuran Brown et al. 1999;Siler et al. 2012 the genus Pseudorhabdion. Below we provide species accounts, notes on natural history, and in some cases, a revised conservation status assessment (with justification) based on International Union for Conservation of Nature categories (IUCN 2022).     with coloration that varies extensively. Its terminal phalanges end in blunt or rounded finger disks that are narrower than those of the toes, and scarcely broader than the widths of digits proximal to disks, as described by Alcala et al. (1998). It also has a few tubercles and some short, irregular folds on the anterior dorsum. This species can be recognized by its high-frequency, single note/pulse advertisement call "click-clickclick … " (Brown et al. , 2013bDiesmos et al. 2015 (Brown et al. , 2013bDiesmos et al. 2015). On Luzon, P. (L.) pygmaeus ranges from 400-1000 m a.s.l. (Diesmos et al. 2015), but we recorded this species at a higher elevation (up to 1557 m a.s.l.) on Mount Guiting-Guiting, which appears to represent a new elevational record. Originally classified as Vulnerable (IUCN 2022), this threat category may no longer be tenable (IUCN 2022), and we agree that the species' conservation status should be downgraded to Near Threatened, given that the original justification, B1ab(iii), relied on the assumption that P. (L.) pyg maeus was reliant on the forest, inhabited a restricted, fragmented forest range, and that this species may have been negatively impacted by habitat degradation (Brown et al. 2013b;Gonzalez et al. 2018)-all of which needs to be re-evaluated in conjunction with the more expansive extent of occurrence established here.  (Alcala 1986;Alcala and Brown 1999;Siler et al. 2007) with digital discs of fingers and toes slightly expanded beyond the width of the penultimate phalanx. Its skin is rugose on dorsal and ventral surfaces, its supratympanic fold rugose and protuberant, and its tympanic annulus is large (9% SVL). Although its advertisement call consisted of frequency sweeps and amplitude modulated notes, similar to the P. (L.) paengi on Panay, full taxonomic verification of its identification has not yet been undertaken. Hence, our tentative assignment of the Sibuyan population to P. (L.) paengi requires further quantitative analysis of advertisement calls and comparison to calls of true P. (L.) paengi at its type locality (northwest Panay Island).

Amphibians
Remarks. Platymantis (Lupacolus) paengi, until now, has been considered a Panay Island endemic, known from Mount Lihidan, a limestone karst mountain of Pandan, Antique Province (Siler et al. 2007;Gaulke 2011). It was commonly observed and collected calling from leaf litter, herbaceous vegetation (<1 m), stumps, and fallen logs, and even in residential areas surrounding the park's borders. The conservation status of P. (L.) paengi has been classified as Endangered (IUCN 2022), but the Romblon Province population of P. (L.) paengi has not yet been assessed taxonomically, which prevents conclusive characterization of its conservation status. Philippine distribution. Panay Island (Diesmos et al. 2015). Further assessment is deemed necessary.   ♀, UPLB-MNH- 3907,3908,3911,3929,[3932][3933][3934][3935]3937,3938,[3940][3941][3942] Identification. Specimens have moderately expanded terminal digital disks and wide lateral dermal flanges along all digits of the hands and feet. Subarticular tubercles have flat ventral surfaces and, like all species of Tira hanulap, P. (T.) lawtoni has greatly reduced first fingers. Its color patterns are highly polymorphic, SVL ranges from 26.0-39.0 mm, yet it can easily be recognized by its tonal (chiming, or ringing) advertisement call. The call is made up of two continuous notes, with the second note of higher frequency than the first, matching the description of Siler et al. (2012).
Remarks. This is a RIG endemic species that is an arboreal shrub frog, or cloud frog, of the Platymantis hazelae group (Brown et al. 2015a) and which has been documented on Tablas and Sibuyan islands but not yet on Romblon proper (Siler et al. 2012). Individuals were observed and heard calling on epiphytic Pandanus sp., from sapling leaves and branches (1-7 m above the ground in lowland forest, 70-1000 m a.s.l.) and 1-3 m above the ground in mossy forests (1100-1560 m a.s.l.); this species has not been observed calling from the ground; all observations were made by us far from the streams. We documented a clutch of six jelly-coated eggs attached to the upper surfaces of a leaf; paternal clutch attendance was observed (CMG pers. obs.). This species has previously been documented at elevation ranges from 300-1200 m a.s.l. (our specimens constitute the lowest and highest elevational records), and in this study, we recorded P. (T.) lawtoni from 70-1557 m a.s.l. (see also Brown and Alcala 1974;Diesmos et al. 2015); thus, our specimens constitute the lowest and highest elevational records ever reported. We noted extreme polymorphic color pattern variation (Fig. 5). This endemic species' conservation status is classified as Endangered (IUCN 2022) based solely on the size of its area of occurrence (most of which occurs within a protected area), so we anticipate necessary revision of this somewhat arbitrary classification. Identification. Platymantis (Lahatnanguri) levigatus is a moderate-size frog (males SVL 21.4-34.0 mm, female SVL 33.0-42.0 mm) with non-expanded digital discs, and slightly smaller finger discs than toe discs. Among all Platymantis, P. (L.) levigatus appears to have unusually smooth and delicate skin (prone to scratches and tears during routine handling by researchers; pers. obs.; Fig. 6). Most individuals were collected or heard calling from rock crevices mid-stream or along banks of fast flowing streams. Notable among all described species of the genus, when disturbed, P. (L.) levigatus jumps, directly into flowing water and often hides in rock crevices. It can be identified by its unique, tonal, peeping advertisement call.
Remarks. This species is a unique RIG endemic member of the subgenus Lahatnanguri (Brown et al. 2015a) and is unusual in that it has a strictly riparian microhabitat preference which, until recently (Brown et al. 2013b), had not been observed in other members of the genus Platymantis. It occurs in the forests of Romblon, Tablas, and Sibuyan islands. This RIG endemic species' conservation status was formulaically classified as Endangered (IUCN 2020) based solely on the size of its area of occurrence (which occurs on Sibuyan in the vicinity of water, along stream banks, within the protected area), so we anticipate necessary revision of this arbitrary classification. Identification. This species' body ranges from mediumsized to large, with SVL 35.5-59.0 mm in males and 50.0-69.0 mm in females. This species belongs to the Fejervarya cancrivora complex, as indicated by its possession of a free dermal flap along the outer edge of the fifth toe (Inger 1954). The head length is slightly greater than its width, the dorsum has irregular skin folds, not arranged in series, the skin on its dorsum and flanks has minute spinules and glandular warts, and the feet are moderately webbed-matching the descriptions by Yodthong et al. (2019) and Inger (1954). Remarks. Individuals were collected along the road of Barangay Tampayan, in a muddy canal near coastal mangroves. This is a widespread non-endemic species that is commonly found near human habitation or disturbed habitats in coastal areas. It has been observed previously on Tablas, Sibuyan, and Romblon in the 2012 study (Siler et al. 2012), and its conservation status is classified as Data Deficient (IUCN 2022 Identification. Body ranges from medium-sized to large (female, SVL 29.9-84.0 mm). We only collected one specimen (male, SVL of 35.0 mm) of this widespread species, but its presence was frequently noted, on the basis of its unique call (below). It can be identified by its head length (slightly greater than width), its more pointed snout (relative to F. moodiei), dorsum with irregular skin folds not arranged in series, skin on dorsum smooth and glandular warts present on its flanks. This species has darkly pigmented bands dark bands, transversely arranged across the dorsal surfaces of the forelimbs and transverse bands on dorsal surfaces of the hindlimbs, and feet moderately webbed. Lastly, we confirmed this identification of the Sibuyan population of F. vittigera, by its loud "honking" advertisement call, frequently heard in other parts of the archipelago Siler et al. 2012;Diesmos et al. 2015).
Remarks. This is a widespread Philippine endemic species that can be found in disturbed habitats. It is also common in land cleared for agriculture and flooded rice fields away from coastal areas. This species has been recorded on Tablas, Romblon, and Sibuyan islands (Siler et al. 2012), and its conservation status is classified as Least Concern (IUCN 2022). Identification. Limnonectes leytensis is a small-bodied Philippine species of fanged frog (adult male SVL 33.0-41.0 mm, female 44.0-49.0 mm) distinguished by its rugose, irregular folded and ridged dorsum, the presence of an Ʌ-shaped mark in the scapular region, and a moderately pointed snout. There species lacks dermal asperities, and its feet have reduced interdigital webbing. These characters match the descriptions of Inger (1954) and Siler et al. (2009). Moreover, the species can be identified by their distinct and unique, loud "shot-gun and flatulence" advertisement call.
Remarks. Individuals of L. leytensis were observed near water sources of various types, ranging from small temporary pools to stream banks, and swamps. In addition to these habitats, we collected individuals from riverbanks, and swamps in a mixed agricultural secondary-growth forest. And the species' conservation status is classified as Least Concern (IUCN 2022). Philippine distribution. Basilan, Bohol, Camiguin Sur, Cebu, Dinagat, Leyte, Mindanao, Negros, Romblon Island Group, Samar, Sulu Archipelago (Diesmos et al. 2015). Identification. This species' adult SVL ranges from 29.0-53.0 mm in both sexes. It has a short snout, with a squat, stocky, and muscular body. It has a small head with orbits situated on the dorsal surface and the skin of its anterior dorsum is slightly corrugated or smooth. The legs are muscular and short with fully webbed feet. Color variation is apparent, with some individuals solid gray or brown and others possessing a light vertebral stripe. The species can be recognized by its uniquely variable advertisement call, which consists of alternating fast (19.0 ms inter-click call interval) and slow (38.0-40.0 ms interclick interval) rates of note delivery; note (click) repetition rate progressively increases across the call. Remarks. It is commonly found in disturbed habitats, and we collected specimens from buffalo wallows and along a small stream, where they were observed in shallow side pools near residential and agricultural areas. We note that in October and November most females were gravid; large clutches of eggs were visible through the translucent abdominal skin. This non-endemic species of puddle frog commonly inhabits shallow muddy puddles, slow-moving streams, temporary and stagnant bodies of water (e.g., buffalo wallows), and side pools of forest streams. This species' conservation status is classified as Least Concern (IUCN 2022   Remarks. Kaloula conjuncta negrosensis was collected at three different elevations between 50 and 1121 m a.s.l., usually from mixed secondary and primary forests. Most individuals were collected in water-filled tree holes near Mount Guiting-Guiting Natural Park's headquarters at Location 1. Individuals were also heard calling from stagnant pools and buffalo wallows in privately owned mango plantations and rice fields, near residential areas, and at shallow pools near the bank of the Jao-asan River. The Kaloula conjuncta group has a patchy and unpredictable distribution that each may warrant specific status (e.g., K. conjuncta conjuncta from Luzon and K. conjuncta negrosensis from western Visayan islands of Panay, and Negros). Recent phylogenetic analysis demonstrated the monophyletic and distinctiveness of each subspecies (Blackburn et al. 2013). Further taxonomic study is needed, given differences in advertisement calls from West Visayan (Negros and Panay) populations and levels of genetic variation distinguishing Romblon versus West Visayan populations (Blackburn et al. 2013 Remarks. Specimens were observed in extremely disturbed areas near human habitation. Voucher specimens were collected from the river banks of the Jao-asan River and a shallow stagnant temporary pool at Barangay Tampayan River near the dam. Individuals were also observed from the mango plantations near rice fields at Sitio Logdeck, Barangay Tampayan, Municipality of Magdiwang. This is a wide-ranging, non-native species (Diesmos et al. 2006) that has been previously recorded in the RIG (Pili et al. 2019;Siler et al. 2012). In the early 1900s, this introduced species was initially thought to be a native species on the islands of Negros, Panay, Sibuyan, and Tablas (Pili et al. 2019). However, due to its disjunct distribution within Borneo, it was suggested that it may have been introduced via the agricultural trade (Inger   Identification. The specimens were identified on the basis of their dark olive cephalic coloration, with three yellow stripes running along each side of the head. The carapace is uniformly dark, elongate, and shallowly domed. Specimens have short stubby tails, a concave plastron, and shorter claws. These are combination of characters that distinguishes males from females of the same species (Barbour and Ernst 1992;Hall 1995).

Occidozyga laevis (Günther, 1858)
Remarks. This Asian box turtle was seen crossing from a water irrigation system to rice paddies on the opposite side of the road leading to the Department of Environment and Natural Resources (DENR) office at Sitio Logdeck, Barangay Tampayan. This species is commonly found in small river systems, streams, ponds, and temporary pools of water. The population of C. amboinensis amboinensis on Sibuyan island continuously faces serious threats from over-harvesting, which account for population declines. Historically, according to locals, Mount Guiting-Guiting Natural Park staff, and local government unit employees, this species experienced extreme hunting and illegal poaching on Sibuyan (see also Diesmos et al. 2008) for the exotic food market, which reportedly reduced their local abundance. This species' conservation status is classified as Vulnerable (IUCN 2022;Uetz et al. 2022 Identification. Bronchocela marmorata is readily identified by its particularly elongate body, with long, slender limbs, and tail. This species is characterized by having a tail more than three times the length of its body (SVL 90.0-98.0 mm vs. tail length (TL) 310.0-342.0 mm). Its body scales are keeled, and its nuchal crest scales are erect, laterally compressed, directed upwards, and somewhat higher (more elongate) than its vertebral crest, which is lower, continuous, with the nuchal crest, with its height decreasing caudally. Dorsal surfaces of the body and limbs are green with black streaks in some individuals collected at Location 1. This is the only species of Bronchocela known from Romblon Province (Siler et al. 2012).
Remarks. Individuals of these species were found asleep at night on branches of trees 3-5 m above the ground. In Barangay Jao-asan, the species was very active during the day and was observed in shrubs surrounding agricultural areas and coconut plantations. This endemic species is widely distributed in the central and northern Philippines. It has been recorded on Sibuyan and Tablas islands in a previous study (Siler et al. 2012 Siler et al. 2012). Enlarged gray blotches are present along the outer margin of the patagia of males (Fig. 13B), whereas in females the patagia have an extensive dark pigmentation (Fig. 13A). The nostrils are laterally oriented and enlarged, thorn-like supraciliary scales are absent, and dorsal scales are variably keeled. Transverse dorsal body scales range 21-33 in males and 15-24 in females. Males can be identified by their lemon-yellow triangular dewlap, absent in females.  Remarks. Individuals were found sleeping on saplings leaves 2-3 m above the ground at night, and others were observed on trunks of trees during the day. A gravid female was found in one of our pitfall traps at Location 2 (326 m a.s.l.), possibly moving on the ground if she was about to lay eggs, which has been observed within the park's borders (RMB pers. obs., 2000). This species has been recorded on Romblon and Sibuyan islands, but not Tablas, where it is replaced by the Luzon/West Visayan PAICs species, D. spilopterus (Siler et al. 2012  Identification. This agamid lizard is distinguished by its robust body, large head, and well-developed nuchal and vertebral crests. Its tail length is nearly twice the length of the head and body combined (TL >200.0 mm vs. SVL >70.0 mm). It can be distinguished by having a strongly laterally compressed tail, with a slightly serrated upper edge, and with regular darkly pigmented bands transversely encircling the tail throughout its length. It possesses a small gular sac, without a serrated anterior edge, and covered by small, strongly keeled gular scales, intermixed with a few more enlarged scales. Dorsal body scales are feebly keeled and intermixed with irregularly scattered, larger tuberculate scales. The ventral scales are moderate in size and strongly keeled. These characters match Boulenger's description (1885). However, the nuchal crest, reported as continuous with the vertebral crest series, is distinctly noncontinuous, that is, interrupted, with an unmistakable diastema between the nuchal and vertebral crests, in the Sibuyan population (Fig. 14). A further taxonomic study should consider the status of the phylogenetically distinct Romblon population (Welton et al. 2017).  Remarks. Specimens were collected at night on branches of trees suspended over the surface of stream pools and on the upper surfaces of large boulders along the banks of the Gaong River. This species of large, semi-aquatic, endemic agamid lizard is often associated with riparian and mangrove habitats. Adults are powerful swimmers and juveniles can locomote across the surface of the water. This species occurs throughout the archipelago, excluding the island of Palawan (Siler et al. 2011c(Siler et al. , 2012 (Welton et al. 2009(Welton et al. , 2010.

Remarks. Individuals of this
Remarks. This species is a Philippine endemic species that was noted to occur in Tablas, Romblon, and Sibuyan islands by Siler et al. (2012). Cyrtodactylus philippinicus is common in low to mid-elevation forests of Mount Guiting-Guiting, and specimens were collected on the bases and trunks (2-5 m above the ground) of trees, usually in close association with riparian habitats, under the bark of dead tree trunks, or underneath rotten logs. This endemic species' conservation status is classified as Least  Identification. Gekko gecko is a large gecko (SVL 87.0-160.0 mm), with bluish-gray body coloration with scattered orange or red spots. It is characterized by the presence of more than 18 subdigital toe IV scansors, presence of tubercles on vetro-lateral folds, absence of femoral pores, and presence of precloacal pores. It can be recognized by the male's loud vocalization, frequently heard at night or early in the morning, which sounds like "tokay!" (Bauer et al. 2008;Wood et al. 2019).
Remarks. It is a widespread, species, known to occur throughout the Philippines. Individual specimens are common in agricultural and residential areas. They are actively observed on ceilings, mango, and coconut tree trunks at night. It can be heard calling in and around residential areas. The conservation status of this common human commensal species is classified as Least Concern (IUCN 2022; Fig. 19   tree trunks 2-6 m above the ground, in mixed second and primary growth forests near sea level. Its conservation status was discussed by Brown et al. (2011a) who noted its apparent rarity compared to its sister species, G. romblon, from Tablas and Romblon islands, despite the protection afforded to G. coi by Mount Guiting-Guiting National Park. Brown et al. (2011a) recommended Data Deficient until the species could be studied in depth on Sibuyan. Philippine distribution. Sibuyan Island Siler et al. 2012). Identification. This small-bodied (SVL 38.0-53.0 mm) house gecko is characterized by its well-developed limbs, moderately dilated and unwebbed digits, a sessile claw on digit I, and a tail generally round in cross section. Its body color varies from gray or light brown to beige, but some individuals have a dark dorsal vertebral line. The forehead is concave, with smaller subcircular auricular opening, 4 or 5 scansors under inner digits, and 9 or 10 subdigital toe IV scansors. The mental is large and triangular, and its rounded tail is covered above with small smooth scales, and transverse rows of 4-6 longitudinallykeeled tubercles per annulus (Boulenger 1885;Brown and Alcala 1978;Vasquez-Restrepo and Lapwong 2018). Remarks. Specimens were collected at night on the ground in the forest, on rocks near Gaong River, and from mangroves. Others were found on walls of houses near outdoor lights, on lamp posts where they were frequently observed preying on insects, in agricultural areas, and on mango tree trunks around the vicinity of the Identification. Our specimens possess 23 or 24 precloacofemoral pores in a continuous series, which is within the range reported for true L. christiani from Negros Island (its type locality; Taylor 1917) and Panay Island (Gaulke 2011). Additionally, body coloration and the repeated dorsal chevron pattern appear to match reports for the species (Brown and Alcala 1978). Siler et al.'s (2012) report of "L. planicaudus" from three islands (Carabao, Tablas, and Sibuyan) could be misidentifications of L. christiani from one or more of these three islands. Although L. planicaudus possesses 28-44 precloacofemoral pores (Eliades et al. 2021), the identification of these populations (only currently represented by old specimens at CAS, for which genetic data are unavailable) will require genetic comparisons to our specimen from Sibuyan, once tissues become available (Eliades et al. 2021).

Remarks.
One male specimen was accidentally caught in a mist net used for capturing bats; no microhabitat preference was noted. However, Lepidodactylus lugu bris, L. balioburius, and L. planicaudus are commonly collected under the dead external layer of the husks around the trunks of banana plants, on leaves of coastal shrubs, or understory trees along forested streams, and also from dead trees in lower-to mid-montane forests (Brown and Alcala 1978;Eliades et al. 2021). This gecko exhibits variable morphology, which requires further study, including genetic confirmation of its affinities, to ascertain possible taxonomic assignment Eliades et al. 2021). Only L. lugubris was previously recorded and reported from Tablas and Carabao islands (Siler et al. 2012). This study appears to be the first to document the occurrence of L. christiani on Sibuyan Island, which is also the first record from Romblon Province. Its conservation status is Least Concern (IUCN 2022; Uetz et al. 2022).

Philippine distribution.
Originally described from Mount Canlaon on Negros Island and has since been reported only from Panay (Gaulke 2011).  Identification. This rare forest gecko species is identified by its moderate to large body size (male SVL 67.0 mm, female SVL 80.0 mm) and its unique combination of characters, including well-developed interdigital webbing, no ventrolateral tail tubercles, and small, granular dorsal body scales interspaced with a few, slightly enlarged dorsolateral tubercles (Gaulke et al. 2007). It has enlarged and imbricate ventral scales and undifferentiated subcaudals; small scales entirely encircle the tail. Remarks. Adult male and female specimens were collected along a stretch of the Gaong River (71 m a.s.l.). The female was caught 1-3 m above the ground at around 23:00 hr on branches and leaves of a bushy tree extending over the river. The adult male was found perched on a vine, also suspended 3-5 m above the river, and only 30-40 m from the female specimen. Forest geckos of the genus Luperosaurus are rarely encountered although they have been recorded from all of the archipelago's large PAIC faunal regions; however, Luperosaurus has never been recorded on Mindoro Island or small landmasses of the RIG (Gaulke et al. 2007;Brown et al. 2011b). This record constitutes the first report of the genus from Sibuyan Island and Romblon Province. Like most of the poorly known species of the genus, L. corfieldi's conservation status is not evaluated (Gaulke 2011). Philippine distribution. Presently unknown, but possibly restricted to the Romblon Island Group and Panay Island to the south (Fig. 1). Identification. Species in the genus Brachymeles generally share elongate, slender bodies with the head weakly differentiated from the neck, poorly developed limbs and limb reduction and loss of digits varying among species. This species can be recognized by its small body size (SVL: males 54.7-74.9 mm, females 52.0-80.9 mm), its elongate, particularly slender shape, head nearly undifferentiated from body, and bidactyl forelimbs and hindlimbs. Additionally, coloration is uniform throughout the body: dorsal, lateral, and ventral surfaces are all medium brown, both in life and in preservative Meneses et al. 2020).

Brachymeles dalawangdaliri
Remarks. In Mount Guiting-Guiting Natural Park, individuals were captured in pitfall traps deployed in combination with drift fencing at elevation ranges of 50-800 m a.s.l. They were also encountered during purposive searches in loose soil under large rocks and rotting logs. The microhabitat of older specimens was unrecorded. This slender skink is a RIG endemic and a member of the Brachymeles bonitae complex (Brown and Alcala 1980;Davis et al. 2016). Brachymeles dalawangdaliri appears to be a forest obligate species. It has been collected from both Tablas and Sibuyan islands.  found that B. dalawangdaliri qualified for Vulnerable status, because it was known from a single small island (B2ab(iii, iv); D2; IUCN 2015). At that time, the species was known only from Tablas, but now that it is also known from Sibuyan, and that a large portion of its range occurs within a protected area, its status should be re-evaluated. We expect it will no longer has a threatened status and that it will eventually be recognized as Least Concern. Philippine distribution. Sibuyan and Tablas islands Siler et al. 2012).   pineal eyespot, supranasals that are in medial contact, and the presence of two enlarged pairs of chin shields .

Brachymeles talinis Brown, 1956
Remarks. This endemic semifossorial slender skink is typically found in dry, decaying forest floor detritus, either inside rotting logs or underneath logs in loose soil. Individuals were captured in pitfall traps set under large rotten logs. The species was recently redescribed in conjunction with a phylogenetic analysis using molecular genetic data to infer its evolutionary relationships with other Brachymeles (Siler et al. , 2011bSiler and Brown 2011). The conservation status is Least Concern (IUCN 2022). Philippine distribution. Probably Guimaras, Inampulagan Island, Negros, Panay, Romblon, Sibuyan, and Tablas islands (Uetz et al. 2022). Identification. Eutropis borealis has a small to mediumsized (SVL 51.0-69.0 mm), robust body, with 66-89 total subdigital toe lamellae, numerous (6-9) pronounced keels in each of its dorsal trunk scales, 35-42 vertebral scale rows, and lateral surfaces with a thick, dark brown band, bordered above and below by light lines, that extends from the eye, to a point beyond insertion of the hindlimbs, at which point the band become thinner and less distinct. This species possesses a creamy-white chin with streaks or dark markings, and its ventrum is grayish tan, with a lighter precloacal region. These traits agree with Barley et al.'s (2020)   Identification. This conspicuous arboreal lizard species can be readily identified by its distinctive, glossy, emerald-green overall body color; some specimens additionally possess dark spots on dorsal surfaces of the head and neck. It has a robust body, with a long and pointed snout, unkeeled body scales, and two enlarged, nuchal scales posterior to parietals. Philippine populations are presently still considered to be an endemic subspecies of the more widespread Pacific Lamprolepis smaragdina .

Lamprolepis smaragdina philippinica
Remarks. This arboreal subspecies is a widespread human commensal with a distinct color pattern Alcala 1970, 1980). It is commonly encountered in disturbed areas and agro-ecosystems with open canopies (e.g., coconut palm plantations and mango orchards). Specimens were found sleeping on a branch of a tree 3-4 m above the ground along the road near a residential area in Barangay Tampayan and were also observed active on the trunk of a coconut tree in Barangay Jao-asan. The conservation status of this species is classified as Least Concern (Uetz et al. 2022 (Linkem et al. 2011), and variable intensity of dark labial region bars on lateral surfaces of the head (Brown and Alcala 1980;Linkem et al. 2011). Our specimens key out to the subspecies P. coxi divergens, which reportedly possesses bold black bars beneath the eye (vertically crossing supralabial and infralabial surfaces), and irregular black markings on the chin (Brown and Alcala 1980). Pinoyscincus coxi di vergens has been genetically confirmed (Linkem et al. 2010b) as a resident on nearby Mindoro Island to the west and Panay Island to the south (Fig. 1). Remarks. Specimens were collected under rocks, from rock crevices, and while basking on rotten logs. Pi noyscincus coxi divergens belongs to the P. coxi jagori abdictus complex, presently understood as an 11-clade group (Linkem et al. 2010b: fig. 3), and additional study of phenotypic characters and genetic variation is needed for definitive identification by comparison to data presented by Linkem et al. (2010b). Genetic confirmation of the Sibuyan population is needed; see Linkem et al.  Identification. This common, generalist, terrestrial skink is identifiable by its medium-sized to large body (SVL 50.0-92.0 mm) and its overall dorsal body coloration of homogeneous dark gray to brown, with light, transverse markings crossing the trunk (Linkem et al. 2010b); it has prominent black bars on lateral surfaces of the head, from the ventral edge of the orbit, bisecting supralabial and infralabial surfaces, and extending ventrally to the chin (Brown and Alcala 1980;Linkem et al. 2010b: fig. 3). Remarks. Pinoyscincus jagori grandis was commonly found under leaf litter. It was trapped in pitfall traps set under large rotten logs or rocks, and it was also captured opportunistically by hand. Pinoyscincus jagori is classified as Least Concern. Genetic data are required to ascertain the true affinities of the Sibuyan population (Linkem et al. 2010b). Philippine distribution. Caluya, Cebu, Masbate, Negros, Panay, Sicogon, Gigante (Uetz et al. 2022). ( 4776, 4778, 4779, 4781, 4785, 4788, 4791. Identification. This skink possesses a diminutive body size (male SVL 51.0-55.0 mm, female SVL 43.0-59.0 mm) and has 36-54 midbody scales, 20-28 toe IV lamellae, four enlarged supraoculars, and a single anterior loreal. It lacks apical pores on dorsal body scales (present on scales of lateral surfaces). The dorsum is brown without dark brown lateral spots. Lastly, both males and females have white throats .

Parvoscincus decipiens
Remarks. This species is similar in color pattern several new species belonging to the P. decipiens complex, which are widely distributed throughout the Sierra Madre Mountain Range (Cagayan and Isabela provinces; . Several specimens were collected from the mid-elevation forest where this species was found in leaf litter, around fallen logs and rocks, or while basking above rocks and rotten logs. This species' conservation status is Least Concern (IUCN 2022;Uetz et al. 2022). The species overall body coloration is reddish to brown, sometimes with light spots extending the throughout length of its body and tail. This skink is identifiable by the presence of dorsal, lateral, and hindlimb apical pores, and the absence of forelimb apical pores . This common, widespread endemic species is one of the smallest species in the Philippines and has been documented throughout the archipelago (Brown and Alcala 1980). On Sibuyan, it is commonly found on the forest floor under leaf litter. Remarks. Although P. steerei can be encountered in a variety of habitat types and throughout the archipelago, its presence is generally associated with some form of vegetation cover, so a conservation status of Near Threatened has been proposed   Welton et al. 2020), with head predominantly black, overlain by occasional small white markings. The trunk has variable numbers of transverse bands of white oscelli, and its limbs are gray to black, with occasional yellow-white spots. It possesses a white or cream venter, with dark transverse bands on the snout. Varanus nuch alis has strongly enlarged, domed nuchal scales, 54 supralabials, and a single enlarged rostral scale. Remarks. Varanus marmoratus is a common West Visayan water monitor that is a genetically distinct endemic species limited to the central Philippines (Welton et al. , 2013b. Masbate and Sibuyan islands are populated by V. nuchalis with a conspicuously melanistic color pattern (Welton et al. 2020: fig.1). It has previously been documented in mixed-agricultural habitat in Mount Guiting-Guiting Natural Park (Siler et al. 2012) and in our study, specimens were caught using snare traps baited with rotten fish. Two individuals were observed in the forest near a rapidly cascading river with steep topography at 306 m a.s.l. One individual was repeatedly observed emerging from a large tree hole, 4-5 m above the ground, and another was observed perched on a branch of a tree, 7-10 m from the ground at 50 m a.s.l. Populations are susceptible to poaching, smuggling, and illegal pet trade (Welton et al. 2020), and this species was treated as Near Threatened (  into multiple smaller scales. Additionally, it is identifiable by the presence of paired internasals, positioned somewhat posterior to the nasals, which are in medial contact. Its dorsal body coloration is near-uniform gray to greenish-brown, or with faint, darker, irregular transverse markings. The species can be differentiated from congeners by the combination of <28 dorsal scale rows at midbody, imbricate and plate-like parietal scales, and the presence of smooth, horizontally divided upper labials (Weinell et al. 2019).

Parvoscincus steerei (Stejneger
Remarks. These fully aquatic, non-endemic homatropine snake, are commonly found in brackish water and estuarine substrates throughout the Philippines (Bernstein et al. 2021). The collected specimen is in Sibuyan's mangrove forests in a coastal area. They were found beneath the surface of shallow, muddy water while actively hunting for prey. Cerberus schneiderii in the Philippines was formerly referred to as the widespread species C. rhynchops until a recent taxonomic revision (Murphy et al. 2012)  Identification. This arboreal snake has a slender body form, with a long, pointed, projecting snout and horizontally oriented pupils. The body coloration varies from gray, dull yellow-green to fluorescent green, with lateral body scale in oblique rows. This species can be identified by the presence of a single, undivided precloacal scale, two or more preoculars, 1-4 small loreals, a single preocular that is in contact with the frontal scale, and its 3rd supralabial scale which does not border the orbit (Weinell et al. 2019).
Remarks. Ahaetulla prasina is widely distributed in the Philippines and this subspecies is endemic to the archipelago (Leviton 1967). Even though its presence on Sibuyan is not surprising, our collections appear to be the first specimen-associated records from the island.
The IUCN (2022) database cites a personal communication from Maren Gaulke (2008) of an observation on Sibuyan, and it is also known from nearby Tablas Island (Siler et al. 2012  Identification. Members of the genus Boiga are large, slender, arboreal snakes, with laterally compressed bodies, distinctly enlarged heads with a rounded snout, with large eyes and pupils oriented vertically. Our B. cyn odon specimen was identified by its overall dorsal body color pattern, which consists of tan ground coloration, accented by irregular bands of yellow, brown, and black; like most examples of this species in the Philippines, our specimen has a conspicuous, thick, dark stripe behind the eye. The species has 23 dorsal scale rows at midbody, three anterior temporal scales, and eight infralabial scales situated anterior to the center of the eye (Leviton et al. 2018;Weinell et al. 2019).
Remarks. This species previously has been reported from the islands of Basilan, Culion, Dinagat, Leyte, Luzon, Mindanao, Palawan, Polillo, Panay, Tablas, and Sibutu (Sulu Archipelago) (Leviton 1963(Leviton , 1970Alcala 1986;Ferner et al. 2000;Gaulke 2001;Siler et al. 2012). We caught our specimen downstream from Location 3 (213 m a.s.l.). It was first observed actively hunting at night, 5-7 m above the ground on a tree branch overhanging a steep rocky stream. Our record is the first from Sibuyan Island. The conservation status of this species is Least Concern (IUCN 2022; Fig. 28). The species has parietal scales in contact with supralabial scales, lacks internasal scales and differentiated temporal scales, and prefrontals are fused into a single shield. It can be distinguished from congeners by 13 dorsal scale rows at midbody and by the presence of a light stripe on the first row of dorsal body scales (Weinell et al. 2019).
Remarks. Generally, this species has been documented frequently in disturbed areas, secondary-growth forests, forest edges, and primary forests (Brown et al. , 2013bLeviton et al. 2018). Our specimens were collected  at three elevation increments where pitfall traps were deployed: 10-148, 213-405, and 576-405 m a.s.l. Others specimens were found coiled in cavities in a rotten log or beneath leaf litter. This is a Philippine endemic species of small, semifossorial snake that is common throughout the Philippines (Inger and Marx 1965). It was first recorded in Tablas and Carabao islands (Siler et al. 2012).
Our specimens from Sibuyan represent the first records from this island. This species is classified as Least Concern (IUCN 2022). Identification. Members of this genus are moderatesized, active, arboreal "flying snakes", possessing a capacity for directed aerial descent, which is unique among snakes. This species can be distinguished from congeners by having 17 dorsal scales rows at midbody, the presence of a divided last ventral body scale, and in the Philippines by its unique overall body color pattern, with light gray or tan dorsal and lateral body surfaces, and variably dark transverse bands (Weinell et al. 2019 Remarks. This is a widespread and semi-arboreal species of snake found in Luzon PAIC Leviton et al. 2018) that is often associated with varied microhabitats of mixed vegetation, forest edges, agricultural, and residential areas. Specimens were found 2-4 m above the ground, coiled, and sleeping on branches or shrubs. Our specimens are new island records for the Romblon Island Group. The conservation status of this widespread habitat generalist species has been classified as Least Concern . Philippine distribution. Luzon (north of the Tayabas Isthmus). Remarks. This is a widespread but uncommon endemic Philippine vine snake, found in central and southern Luzon (i.e., Mount Makiling, Bataan, Zambales, southern Cordillera Mountains), Mindoro, Marinduque, Panay, Negros, Siguijor, western Mindanao and Sibuyan Island (Brown et al. , 2013bLeviton et al. 2018). It is arboreal but so seldomly observed, that we have very little information about its specific microhabitat preferences (Gaulke 2011;Leviton et al. 2018 (Leviton et al. 2018). Remarks. An endemic Philippine terrestrial snake known to be Panay, Negros, and Tablas islands (Leviton 1963;Leviton et al. 2018 Identification. This genus is represented in the Philippines by a single species, which is readily distinguished by its large body size (SVL: 805.0-1372.0 mm; TL: 239.0-426.0 mm), projecting and elongate snout, typically emerald green color throughout the body with a dark red tail, and smooth dorsal scales in 23-27 rows at midbody (Weinell et al. 2019). The Sibuyan population, however, appears unique in that there are two distinct color dimorphisms: the typical green morph, and a unique, golden-yellow phase (Fig. 33).

Oligodon modestus
Remarks. This Red-tailed Green Rat Snake is a nonendemic, widespread species, found throughout Southeast Asia. This genus is represented in the Philippines by a single species. It is known to occur in almost all major islands of the Philippines (Alcala 1986;Gaulke 2011;Leviton et al. 2018). Specimens were collected at between 576 and 939 m a.s.l., atypical snake species occurrence that was recorded for the first time from an unusually high elevation and one was found asleep on a tree branch (UPLB-MNH-Z-NS 4936: 6-7 m high above the ground) and another was first observed resting on a large fallen log (UPLB-MNH-Z-NS 4935). At Barangay Jao-asan (25-37 m a.s.l.) we observed a greenish morph individual asleep and coiled around a tree branch, 7-10 m high, overhanging a river at night. In 2013, a road-killed specimen was reported from the Cabitangahan River area (Sy and Tan 2013). Our one goldenyellow morph individual (UPLB-MNH-Z-NS 4935) from Mount Guiting-Guiting Natural Park is considered the first record for the protected area.
The conservation status of this widespread nonendemic generalist species is classified as Least Concern Leviton et al. 2018). Philippine distribution. Babuyan Islands (Calayan and Camiguin Norte provinces), Balabac, Bataan, Bohol, Di-  nagat, Leyte, Lubang, Luzon (Aurora, Ilocos Norte, Isabela, Laguna, Nueva Vizcaya, Quezon, Sorsogon, Zambales provinces), Marinduque, Mindanao (Agusan del Sur, Davao Oriental, South Cotabato, Surigao del Sur provinces, Zamboanga City), Negros, Palawan, Panay (Aklan, Antique, Iloilo provinces), Sabtang, Sibuyan, and Sulu Archipelago (Bongao Province) (Leviton et al. 2018). Leviton, 1967  , head only slightly distinct from neck, eyes small with round pupils, and unique dentition (Gaulke 2011); they also have unusually high numbers of subcaudal scales (Weinell et al. 2019). Our confirmation of the Sibuyan population as Cyclocorus lineatus alcalai is based on Leviton's (1965) original diagnosis, emphasizing two anterior temporals, eight supralabials, 142-159 ventrals, 33-53 undivided (single) subcaudals, cloacal scale single, venter dark, with irregularly triangularly-shaped blotches well-developed only along the lateral edges of ventral shields. Remarks. Cyclocorus is one of four snake genera endemic to the Philippines (Brown et al. 2013b) and Cy clocorus lineatus alcalai is the West Visayan endemic subspecies found in Negros, Cebu, and Panay. Previously, it was noted on Tablas Island (Leviton et al. 2018;Siler et al. 2012). Individuals in this study were found at three elevation sites (Locations 1-3, with elevations ranging from 300-939 m a.s.l.), in two different habitat types: lowland and montane forest. Individuals were found actively crawling under leaf litter near stream banks, on a forest trail, and under rocks. Recently, a male individual was reported from Sibuyan Island and recorded from Barangay Jao-asan secondary forest (Pili and Del Prado 2018). Cyclocorus lineatus' conservation status is classified as Least Concern (IUCN 2022;Leviton et al. 2018). Philippine distribution: Cebu, Guimaras, Inampulugan, Negros (Negros Occidental, Negros Oriental provinces), Panay (Aklan and Antique provinces), and Tablas (Leviton et al. 2018). Identification. This semi-aquatic species is mediumsized (TotL: 723.0-750.0 mm), with moderately elongated body and tail, dorsal scales strongly keeled, head distinctively enlarged relative to its neck, and with large eyes (with large, round pupils) and a divided cloacal scale. This natricine species has a pale nuchal spot, 17 rows of dorsal scale rows at midbody, and pale ventral coloration (Weinell et al. 2019). Remarks. This natricine species is commonly recorded at low elevation areas throughout the archipelago (Leviton et al. 2018;Malnate and Underwood 1988). On Sibuyan Island, specimens were collected at two sites: at 71 and between 213 and 260 m a.s.l. These sites are mixed agricultural, second-growth forest, and primary  growth forests. This is a Philippine endemic that was not previously recorded in Romblon Province, and this record from Sibuyan also represents a new island record. Specimens were observed actively crossing rocky trails at both sampling sites during the daytime. The conservation status of this widespread species is classified as Least Concern (IUCN 2022  Identification. Our specimen was compared to older museum collections (CAS 169979) and the redefinition of the M. ruficaudus group, provided by Wynn et al. 2016), and we initially noted its general body size, short tail (broader than long; McDowell 1974), and stratified body color pattern: dark brown dorsum, demarcated from lighter yellow ventrals. In this species, dorsal body transverse rows between head and tail are fewer than 350, and the rostral scale is rounded. The total length (TotL) of our specimen is 246.0 mm (Weinell et al. 2019).

Cyclocorus lineatus alcalai
Remarks. An endemic Philippine species of blind snake that, like so many fossorial species, is poorly known due to a paucity of specimens and a problematic history of specimen misidentification (Wynn et al. 2016). It has been recorded from Luzon, Marinduque, Tablas, and Sibuyan (CAS 169979; Leviton et al. 2018). Little is known about the species' habitat and ecology. We collected an individual at 306 m a.s.l., where it was captured (between 06:00-07:00 hr) in a pitfall/drift-fence trap, installed under a large, rotten dipterocarp trunk and thick leaf litter. This cryptic species' conservation status is  Identification. This entirely aquatic marine sea snake has an elongate, cylindrical body, short indistinct head, blunt snout, and a laterally compressed tail. It has an attractive silver and black banding pattern that covers the entire body, from its neck to the tip of its tail. This species has an undivided rostral scale, nasal scales separated (internasal scales present), and a yellow upper labial region; additionally, the width of its ventral body scales is exceeds 1/3 of its body width and its total length (TotL) is 608.0 mm (Weinell et al. 2019). Remarks. Laticauda colubrina is a widespread sea snake, which we recorded in coastal habitats in the vicinity of Lambingan Falls. One individual was found crossing sand, as it moved from rocks to the seashore at 22:00 hr; another was found dead behind boulders, 20 m from the shore (presumed killed by residents known to hunt octopus and crabs after dark). This species is found in a wide range of marine microhabitats, including shallow  waters surrounding Sibuyan Island.
It was previously recorded on the coast of Maestre de Campo Island (part of Romblon Province) by Siler et al. (2012) although records from coastal northwest Panay may constitute the most geographically proximate previous record of the species' regional occurrence. Leviton et al. (2018), in summarizing the species' distribution, found no records of the species in the seas surrounding Romblon, Tablas, or Sibuyan islands, and, as such, our record appears to be the record of the species for Sibuyan Island and Romblon proper. This non-endemic species' conservation status is classified as Least Concern (IUCN 2022 (Leviton et al. 2018).

Discussion
Our study highlights the degree to which underestimates of species diversity can persist problematically through time, mostly as a result of a lack of deliberate, focused attention to study design, methodology, and study replication. By emphasizing seasonal/atmospheric (i.e., rainy season and dry season, survey and resurvey sampling regime) and environmental and microhabitat variation (such as sampling an extensive elevational gradient), we added numerous species of high conservation value to the total documented amphibian and reptile fauna of Sibuyan Island. In some ways, our results are concerning and should be taken as a warning about the pitfalls associated with negative data or the assumption of completeness of species diversity estimates for an area such as a particular island, protected area, or even an established national park. Even after an apparent comprehensive inventory (Siler et al. 2012) built on years of intensive local fieldwork (Brown and Alcala 1974, 1978, 1980 in a celebrated protected area that had been considered reasonably well characterized (Goodman and Ingle 1993;Goodman et al. 1995;Allen 2006), we were still able to increase Sibuyan's known herpetological species diversity by 21% (Tables 1-3). This has become a pattern with repeated, survey-and-resurvey, follow-up field studies (Brown et al. 1996(Brown et al. , 2013bDiesmos et al. 2004;Siler et al. 2011c;Devan-Song and Brown 2012) and serves as a continuous reminder of the crucial need for regular, ongoing, repeated biodiversity inventories, surveys, and re-estimates of species diversityparticularly in high conservation value sites like national parks and other protected areas. This is of utmost importance in Philippine National Parks where increased bureaucratic and administrative oversight (often as part of protected area management boards in collaboration with indigenous peoples' groups), and a very understandable and justified effort to protect biodiversity can result in strong sentiments and policies against hunting or commercial collecting of animals . Unfortunately, if commercial versus scientific faunal collecting is not clearly defined, and legislatively distinguished at national and local levels, a general tendency to discourage the collection of any specimens from within protected areas may result ). In the case of Sibuyan's protected area, it is clear that incomplete knowledge of amphibians and reptiles species diversity, and a shortage of information on their patterns of distribution and habitat requirements within Mount Guiting-Guiting Natural Park has negatively impacted conservation management priorities, and misinformed policy assessments, even though Mount Guiting-Guiting is widely recognized as a high-value conservation priority and federally managed protected area (Goodman and Ingle 1993;Goodman et al. 1995;Heaney and Regalado 1998;Rickart et al. 2005;Esselstyn and Goodman 2010).
The data we have presented paints a revised picture of Sibuyan Island's herpetofauna, particularly Mount Guiting-Guiting amphibian and reptile diversity-which is still far from completely known (Table 1). Here we augment a growing body of extensive scientific literature on Sibuyan Island biodiversity, with new and up-to-date data, including many surprises and discoveries, which build directly on the study of Siler et al. (2012), with the notable addition of species by Supsup et al. [2016]), which was synthesized data from six Romblon Province islands and 28 surveyed localities, resulting in the documentation of 56 species of amphibians and reptiles. A review of the summarized records from the 2012 and 2016 reported observations, combined with specimenassociated data from vouchered records among all global museum collections, resulted in the identification of nine new geographical records for Tablas, eight for Romblon, five for Sibuyan, and five for Maestro de Campo (Siler et al. 2012).
We summarize the results of the past and the previous survey, providing extensive new specimen-based data for a total of 63 species of amphibians and reptiles. These include one introduced species, 53 Philippine endemic species, and nine non-endemic species; 13 species of frogs, 30 lizards, one turtle, and 19 snakes, distributed among 18 families and 46 genera (Table 1). Recently collected data consisted of 14 amphibian and reptile species recorded for the first time from Sibuyan Island and maybe the RIG and one substantial elevational record for the snake, Gonyosoma oxycephalum (742 m a.s.l.) (Table 1).
Our resurveys increase Sibuyan's herpetological species diversity by an 21%. This substantial proportional increase possibly results from sampling different drainages, different microhabitat types, and sampling a wider range of elevations-all known axes of environmental variation documented to have distinct herpetofaunal communities (Brown et al. 1996(Brown et al. , 2013bDiesmos et al. 2004;Siler et al. 2011c;Devan-Song and Brown 2012). This posits the importance of repeated visits, a combination of sampling techniques, focusing on different times of the year, covering sufficiently broad ranges of distinct habitat types, and targeting different elevations characterized by variable atmospheric, precipitation, and temperature conditions. Exhaustive and repeated sampling approaches have the potential to fill in gaps in biodiversity data, that have plagued earlier studies which were unable to offset or account for the oftenpatchy distributions of many amphibian and reptile species in a given area (Diesmos et al. 2005;Diesmos and Brown 2011;Oliveros et al. 2011;Siler et al. 2011c;Brown et al. 2013b). We consider a 21% proportional increase in Sibuyan's herpetological biodiversity to constitute an important accomplishment, given the previous lack of information on amphibian and reptile diversity in the protected area situated on such a celebrated mountain, Mount Guiting-Guiting. All 21% constitute significant records or range extensions for the recognized species.
Because of the geographic position of Romblon Province, which is situated between three major adjacent island banks, and distinct Philippine faunal regions (the Luzon, Mindoro, and the West Visayan PAICs; Brown and Diesmos 2009), we used simple Simpson similarity indices to evaluate the degree to which each surrounding region has possibly served as a biogeographic source for Sibuyan's species and which uniquely assembled to form the remarkable and biogeographically noteworthy herpetofauna of Sibuyan. Siler et al. (2012) concluded that, with few exceptions, the Luzon, Mindoro, and West Visayan PAICs had contributed disproportionately to the faunal diversity they found on the islands of Romblon Province. One exception is Carabao Island, wherein the degree of similarity indicated a simple West Visayan PAIC origin of that island's fauna, which makes sense given its geographic position, between Tablas and Panay islands. In this study, the biogeographical species affinities for Sibuyan' herpetofauna were skewed towards the Luzon PAIC (76%), followed by West Visayan PAIC (75%), then the Mindoro PAIC (73%) (Tables 2, 3). Siler et al. (2012) estimated these same similarities at 77%, 74%, and 66%, respectively. The similar proportional similarity estimates may be because we include some widespread species (i.e., Ahaetulla prasina preocularis and Gonyo soma oxycephalum) which we would expect to find on most Philippine islands (Brown and Alcala 1970;Leviton et al. 2018) among the 14 additional species added by our study. However, we also take note of important new Sibuyan records for species that most likely have Western Visayan PAIC and Luzon PAIC biogeographical affinities: Oligodon modestus, Pseudorabdion talonuran (phenotypically similar to P. talonuran from Panay), Lu perosaurus corfieldi (morphologically intermediate between L. cumingii [Luzon] and L. corfieldi [Panay]) and D. luzonensis, respectively. We do not doubt that with the constant field research, and application of new industry-standard technologies (DNA sequencing, bioacoustics monitoring) many new and interesting herpetofaunal discoveries will be recorded and that other interesting biogeographical relationships with the surrounding PA-ICs will be revealed (Tables 1, 2).
Two species of frogs (Platymantis lawtoni and P. lev igatus) are assessed by the IUCN (2022) and Amphib-iaWeb (2022) as Endangered; two species of lizards (Parvoscincus steerei and Varanus nuchalis) are listed as Near Threatened; four species (one species of lizard: Hydrosaurus pustulatus; one species of a turtle: Cuora amboinensis amboinensis; and two species of snakes: Dryophiops philippina and Oligodon modestus) are listed as Vulnerable; and four species (one species of frog: Fejervarya moodiei; two species of lizards: Bron chocela marmorata and Gonocephalus sophiae; and one species of snake: Malayotyphlops ruficaudus) are listed as Data Deficient. Several endemic species have not yet been assessed, including two recently described gekkonid lineages (Gekko coi and Pseudogekko isapa); two species of scincid lizards (Brachymeles dalawang daliri and Pinoyscincus jagori grandis), and one species of homalopsine snake (Cerberus schneiderii). In addition, we tentatively identified 10 species that need confirmation, and therefore, we recommend additional specimen-based evaluations of these taxa, including genotyping, for verification (Platymantis pygmaeus, P. paengi, Kaloula conjuncta negrosensis, Gonocephalus sophiae, Lepidodactylus christiani, Luperosaurus cor fieldi, Pinoyscincus coxi divergens, Parvoscincus decip iens, Pinoyscincus jagori grandis, and Pseudorabdion talonuran) (Table 4). Aside from this list of uncertain taxa, there are two unidentified species of frogs from the genus Platymantis recorded in high-elevation habitats of Mount Guiting-Guiting Natural Park not included in our annotated list of species.
In Table 4, we showed evidences of species' unresolved uncertainty that requires future taxonomic reconsideration, it showed that all Platymantis are new since Siler et al. (2012). Our tentative identification of P. paengi and P. pygmaeus were mainly based on the close relationship of these species to P. pygmaeus in Luzon and P. paengi in Panay based on the initial result of our molecular analysis. The unresolved uncertainty of the morphological data of the Platymantis populations on Sibuyan as compared to the true and identified species suggests that additional studies are needed before we can confidently establish their identities. The same uncertainties were observed with the other species. Kaloula conjuncta negrosensis displays phenotypic similarities (like color pattern and overlapping SVL) and shares microhabitat preferences, but exhibits a different advertisement call. Lizard species such as Gonocephalus sophiae, Pinoycin cus coxi divergens, Parvoscincus decipiens, and Pinoy scin cus jagori grandis require integrated taxonomic studies to delimit unresolved species complexes. Lastly, Pseudarabdion talonuran, specimens exhibit some physical characteristics similar to P. mcnamarae which has been recorded on Tablas and Sibuyan islands (Siler et al. 2012) but our specimen is similar in other respects to the true P. talonuran, a Panay Island high-elevation endemic recorded from Mount Madja-as . Its large size precludes us from confidently assigning it to P. talonuran, and our specimen requires additional close comparison to P. macnamarae and P. talonuran and genetic analysis before we can confidently establish its taxonomic identity. Similarly, our specimens of Luperosau rus corfieldi, are morphologically similar to L. cumingii and L. corfieldi but cannot be reliably identified as either species, and we are hesitant to include this species in our list until genetic data can be analysed.
Our survey also discovered two undescribed highelevation species of Platymantis; Platymantis cf. polil lensis (temporary identification), which belongs to the Platymantis hazelae group according to Brown et al. (2015a) based on information from Brown et al. (1996). The Sibuyan Island population is phenotypically most similar to P. polillensis. Its SVL ranged from 21.5-26.1 mm, based on six individuals with similar morphological characteristics. They were observed in shrubby vegetation, at the peak of Mount Guiting-Guiting. This arboreal species can be distinguished from its sympatric congener, P. lawtoni, by its uniformly yellow body and bluish eye ring, both typical of P. polillensis, but the uniform body coloration was only observed at the highest elevations (1557 m a.s.l.) along our elevational transect. Despite the morphological distinctiveness of this Mount Guiting-Guiting peak population (which, alone, is usually not sufficient for identifying species with a highly polymorphic color variation like Platymantis), we hesitate to describe this potentially distinctive species because we were unable to obtain advertisement call recordings. Thus, acoustic and molecular data are needed (e.g., Brown and Gonzalez 2007;Siler et al. 2007;Brown et al. 2015a).
The second unidentified Platymantis, Platymantis cf. dorsalis (previously reported nomen; collected at higher elevations) is from the P. dorsalis group. It is clearly of the subgenus Lupacolus (Brown et al. 2015b) and was collected from elevations of 55-1557 m a.s.l. within Mount Guiting-Guiting Natural Park. Individuals collected at 1121-1492 m a.s.l. have notably extensive morphological and microhabitat preference variation, and at these higher elevations, individuals were observed calling on branches of trees or saplings, on the ground near large boulders, within leaf axils of Pandanus, perched on top of fallen logs, and on the tops of rocks and leaf litter on the forest floor. The SVL of an adult male and female ranges from 18.0-55.0 mm, and the higher elevation form resembles P. paengi (uncertain species: from lower elevations; with SVL of 23.0-30.0 mm). It is conceivable that the high-elevation form is a variant of the same species (P. paengi) but that at higher elevations, the colder environmental conditions have locally selected a substantially larger body size (consistent with Bergman's Rule; Olalla-Tarraga and Rodriguez 2007; Liao et al. 2016;Guo et al. 2019;Yu et al. 2019). However, this hypothesis warrants further study of intermediate elevations and body sizes, and overall verification, with molecular and bioacoustic data.
Aside from taxa potentially new to science, our study also provides many new records and geographical range extensions for previously known species of amphibians and reptiles. Our study updates the species list from Sibuyan by including specimen-associated data and properly prepared scientific specimens now archived in publicly accessible biodiversity repositories. These collections, like conservation and research resources, not only allow future verification of uncertain species identifications but also for complete taxonomic description in the event that any are determined to be new species. The increase in the number of Sibuyan species detected, including new island records and possibly new species, all from a single island and a formerly poorly surveyed protected area, emphasizes how much more there is to learn about the fauna of Sibuyan Island, despite historic interest and a rich tradition of literature (Alcala and Alviola 1970;Brown and Alcala 1970, 1974, 1978, 1980Heaney 1986;Dickinson et al. 1991;Goodman and Ingle 1993;Ingle 1993).
We observed a clear decline in amphibian and reptile species diversity with increasing elevation: herpetological diversity was highest at our low-elevation sampling areas and, conversely, lowest at higher elevations (Fig. 38). Previous studies have observed this same pattern: generally, the archipelago's richest herpetofauna diversity estimates have been recorded in lower montane forests, including moderate percentages of Philippine-endemic species, with species diversity varying inversely-proportional to elevation (however, higher proportions of Philippine-endemic species result from wellstudied sites at higher elevations; Brown et al. 2000;Siler et al. 2012;Supsup et al. 2020).
Biogeographers and conservationists recognize that former dry land exposure forged connections among modern islands during Pleistocene sea-level oscillations, which influenced the assembly and partitioning of terrestrial biodiversity and may have in part contributed to the evolution of some taxa by means of isolation and divergence (Taylor 1928;Inger 1954;Heaney 1985;). Considering that Sibuyan Island is separated on all sides by deep-water channels, it is not surprising that the island harbors largely distinct biological communities, derived from faunal elements bearing biogeographical relationships to the surrounding adjacent landmasses Alcala 1974, 1978;McGuire and Alcala 2000;Siler et al. 2012Siler et al. , 2016.
Past considerations of the biogeographical relationships of Sibuyan's fauna (Brown and Alcala 1970;Esselstyn and Goodman 2010;Goodman et al. 1995;Siler et al. 2012) emphasized their perspectives, derived from amphibians, reptiles, birds, and mammals, that the unique species assemblages on Sibuyan were all ultimately derived from over-water dispersal, colonization, and in the case of the island's endemic species, subsequent isolation and divergence (Brown and Alcala 1970;Gillespie 2013;). It is assumed in such cases, that the combined effects of isolation and time have allowed for the development of Sibuyan's unique, biogeographically combined biota. Thus, there is much to be learned from natural patterns of diversification even on this single island; dimensions of biodiversity patterns associated with isolation, topography, climate, habitat structure, species interactions, and individual species' microhabitats should all be the subject of future studies on Sibuyan using continued integrative and multidisciplinary research.
From a conservation perspective, a rapid loss, extirpation, or extinction of Sibuyan's biodiversity remains possible-even in its large, protected areas-as a consequence of the underestimated estimates of its biodiversity. Sibuyan's amphibians and reptiles face continuous threats via incessant anthropogenic activities, including poaching, forest habitat degradation, and overharvesting (Siler et al. 2012;Welton et al. 2013aWelton et al. , 2013bWelton et al. , 2020. Curtailing or restricting legitimate scientific research only serves to undercut management of protected areas for the simple reason that protected areas need biodiversity information to prioritize the conservation value of individual species, identify threats, fuel public education, increase environmental awareness, and enhance local stakeholder pride and engagement.
Aside from the impact on taxonomic and biogeographical studies, incorporating enhanced biodiversity data collection and regular, periodic monitoring, will provide a tractable, mechanistic strategy for future effective, sustainable, data-driven, and Sibuyan-specific conservation programs. Engaging civic-minded Sibuyan residents in citizen science efforts may be particularly effective if combined with a collection of photographic records, genetic samples, and passive environmental monitoring of frogs using acoustic data. Increased and IT-enabled collection of scientific data combined with insights from local community stakeholders will provide essential information in the formulation of appropriate management strategies directed toward the conservation of amphibian and reptile diversity in Sibuyan-and the Philippines in general.
Sibuyan Island's rich amphibian and reptile diversity could be utilized to enhance the public's appreciation of the Philippines' conservation value via promotional campaigns (e.g., former "More Fun in the Philippines, the Galapagos of Asia") and other proven tools for public education. This is because Sibuyan embodies an extreme biological "island syndrome" case study in which, in addition to Mount Guiting-Guiting Natural Park's striking land-and-seascape beauty, clearly exhibits (1) an island characterized by extreme isolation, (2) a truly "oceanic island" with no history of connection to any surrounding landmasses, and (3) high species diversity, present in a unique combination of amphibians and reptiles, that colonized Sibuyan from at least three different sources, and (4) a surprisingly high proportion of Sibuyan-endemic species: distinct species that ecotourists can find nowhere else on Earth (i.e., P. levigatus, P. lawtoni, Brachymeles dalawangdaliri, Pseudogekko isapa, and Gekko coi).
Finally, within this tiny island is a remarkable array of distinct and accessible classes of environments: five forest types, each representing unique environments: (tropical lowland evergreen rainforest, unique forests of limestone formations, forest associated with ultramafic rock, coastal beach forest, and mangrove forest. Sibuyan supports 70-80% uninterrupted forest cover and is one of only a few places left in the Philippines where intact ridge-to-reef continuous elevational gradients still exist as they did before the arrival of the first European conquistadores (Tongson and McShane 2006). Given its unique flora and fauna, the island should remain a priority for sustainable conservation efforts, which will require enhanced mobilization of resources associated with environmental protection and collaboration at local, national, and global scales.