Distribution and Diversity of Fiji’s Terrestrial Herpetofauna: Implications for Forest Conservation

In 2003 The Wildlife Conservation Society attempted to evaluate the conservation status of Fiji’s natural forests including identifying a series of biological provinces (based on the distribution and endemism of a number of terrestrial taxa) in which some form of conservation area would need to be established or maintained. A combination of literature surveys, consultations with local researchers, and targeted field surveys was used to identify herpetological provinces within Fiji. With the exception of the iguanas (restricted to dry forest habitats), the frogs, and one of the skink species (restricted to wet forest habitats), the herpetofauna of Fiji is widespread in terms of both geography and habitat type and consequently there are no real distinct species assemblages or communities. Based on areas with the highest levels of herpetofauna species richness and endemism, forest reserves need to be established or maintained on Yadua Taba, Taveuni (particularly the northern and eastern sides), Ono-i-Lau, Ovalau, Gau, Rotuma, and the Monasavu area of Viti Levu to maximize conservation of herpetofauna diversity. Because there are gaps in the knowledge of geographic distributions of species resulting from incomplete surveys of several areas of the country, further targeted surveys are needed to completely evaluate the distribution of all herpetofauna species in Fiji. Fiji’s forests and wildlife are a unique blend of ancient continental groups and more recent arrivals from across the oeans that have diversified. The resulting forest ecosystems are still distinctly islandlike but are exceptionally species rich (Mitchell 1991, Ryan 2000). Many species and species groups occur only in Fiji, including an entire family of plants (Degeneriaceae), two unique iguanas, an endemic snake genus (Ogmodon), and a wealth of plants and invertebrates, many of which are restricted to single islands, mountaintops, or watersheds (Ryan 2000). Nearly 40% of Fiji’s forests remain intact, and on some islands there are large expanses of forests extending from mountaintops (>1,000 m) down to the coast, thereby offering one of the few opportunities to conserve large blocks of rain-forest wilderness in the South Pacific. To date the conservation importance of Fiji forests has been largely overlooked by global and regional conservation analyses. In 2003 The Wildlife Conservation Society evaluated the conservation status of Fiji’s natural forests as part of its ‘‘Conservation of Fiji’s forests and wildlife: Building conservation landscapes into forestry operation and forestry certification’’ project (Farley et al. 2004). A herpetofauna survey was conducted as part of the overall Wildlife Conservation Society project to determine herpetological provinces that might be used to evaluate representation in Fiji’s current forest reserve network. The known terrestrial herpetofauna of Fiji consists of 30 species: 3 frogs, 2 iguanas, 3 snakes, 10 geckos, and 12 skinks. Forty perPacific Science (2005), vol. 59, no. 4:481–489 : 2005 by University of Hawai‘i Press All rights reserved 1 This project was funded by The Wildlife Conservation Society as part of its ‘‘Conservation of Fiji’s Forests and Wildlife: Building Conservation Landscapes into Forestry Operations and Forest Certification’’ project. Several of the field trips (Viwa, Viti Levu) were funded by the Pacific Biological Foundation. Manuscript accepted 7 October 2004. 2 Institute of Applied Sciences, University of the South Pacific, Suva. Fiji. (e-mail: [email protected]). cent (12/30) of these species are endemic to Fiji, and a further 40% are considered native species. The remaining six species (20%) are human-mediated colonizers (Morrison 2003). To date, work on the distribution and abundance of Fiji’s herpetofauna has been fairly limited in scope. The work done by George Zug, Dick Watling, Paddy Ryan, Stanley Gorham, and other researchers has provided valuable information on the species; however, there remain many large gaps both in our knowledge and in areas of the country that are yet to be surveyed. Consequently, the aims of this study were to (a) determine the geographic distribution of all species of terrestrial herpetofauna within Fiji; (b) identify preferred habitat types of all species; (c) identify herpetological assemblages and/or communities found in different habitats; and (d) identify areas of high species richness or endemism that should be included in Fiji’s forest reserve network. materials and methods Data were collected in three ways: (1) from an analysis of published and unpublished literature, (2) from consultations with other researchers familiar with these taxa in Fiji, and (3) from targeted field surveys. Key references used in data collation were Gibbons (1981), Gorham (1968, 1970), Morrison (2003), Ryan (2000), Shea (1995), and Zug (1991, 1995). Targeted visual encounter surveys (VES) were carried out in Taveuni, Viti Levu, Gau, Viwa, and Vanua Levu between February and October 2003. Fixed-effort (16 person hours) diurnal and nocturnal surveys were carried out in a range of habitats on each of the islands. Data collected included presence/ absence of herpetofauna species, habitat, and microhabitat types. Habitats on each island were assigned to one of nine vegetation classes based on Mueller-Dombois and Fosberg’s (1998) description of the major vegetation types found in Fiji (and other Pacific Islands). Lowland rain forest is found in the wet zone of the high islands of Viti Levu and Vanua Levu and extends from near sea level to an altitude of 600 m, with a mean annual rainfall of 2,000–3,000 mm. Upland rain forest occurs mostly in areas above 600 m in both the wet and dry zones, the latter toward the interior of the large islands. These areas receive a mean annual rainfall of 2,000–3,750 mm. The cloud forests are mainly enshrouded in clouds and are restricted to mountaintops and ridges above 600 m near the coast and higher than 900 m inland with more than 9,000 mm of annual rainfall. Dry forests are only known to occur in parts of the dry zone of Viti Levu and Vanua Levu and some of the western islands. Rainfall is very low, with a mean annual range of 1,750–2,250 mm. Talasiga vegetation is dry-zone vegetation found in fire-degraded environments and spreads from sea level to 1,000 m. It receives a mean annual rainfall of 1,500–2,500 mm. The freshwater wetland vegetation occurs only in the wet zone of Viti Levu in poorly drained alluvial sites along coastal flatland along the Rewa and Navua Rivers and is dominated by ferns, grasses, and sedges. Mangrove forests are associated with river estuaries and are found along the coastline. Moving landward, coastal stand vegetation changes from creepers and herbs to shrubs and trees. On Viti Levu such vegetation is only found on the northeastern coast, where human habitation is not as dense. Smallisland vegetation is a combination of coastal stand vegetation, mangrove forest, and talasiga vegetation. These islands receive a mean annual rainfall of approximately 2,000 mm.