Lizard diversity patterns along disturbance gradients in polillo island: implications for effective conservation

An ecological study of the lizard species in Polillo Island (c. 350-400m elevation) was conducted for a period of two months (July-September, 1999). Drift fences in conjunction with pitfall traps and intensive searching that utilizes a plot as sampling area, constituted the sampling techniques employed in the field. Using these two methods to sampling lizard populations, diversity patterns using standard diversity indices (i.e. Shannon-Weaver Indices) were computed and ecological relationships among the different habitats were determined. A total of 783 individuals belonging to 25 species in four genera were recorded from the island. Four of the 25 species are new island records. Of the four groups of lizards, family Scincidae is the most represented taxon, followed by Gekkonidae, Agamidae and the Varanidae to which the endangered and endemic Varanus olivaceus belong. Across disturbance gradients, primary forest harbors the most number of species with a total of 11 followed by the secondary growth with eight species and agro-ecosystem with only five. Species diversity is highest in the primary forest and lowest in the agro-ecosystem. Likewise, endemicity was observed to be highest in the primary and decreases as the species go towards the more disturbed habitats. The trends in the diversity patterns as observed among the lizard fauna on the island largely contributed to the assessment of the existing faunal population. Several conservation measures for the protection and conservation of the species were recommended for the sustainability of the species and their remaining habitats. Introduction Made up of more than 7,100 islands and islets, the Philippine Archipelago lies between South China and the Greater Sunda Islands, but zoogeographically it is a fringing archipelago extending northeast from Borneo for nearly a thousand miles (Darlington, 1957). Heaney (1985) divided the entire archipelago into six faunal regions as defined by the extent of the Pleistocene islands – Greater Luzon (this include Luzon island and the adjacent islands of Catanduanes, Marinduque and Polillo), Greater Mindanao, Greater Palawan, Greater Mindoro, Greater NegrosPanay and Greater Sulu. The entire island is home to various floral and faunal assemblages, unique only to the region. At present, more than 1,700 species of vertebrates are found in the Philippines, most of which are island endemics (Dans and Gonzalez, 1998). Among the 224 reptiles that have been recorded from the island, 123 species are lizards, 97 of which are endemic. Gonzalez, 1995). Although the Philippines is regarded as one of the major centers of biological diversity (“biodiversity”) and endemism due to its unique and exceptionally rich biota it is also considered as one of the world’s biodiversity “hotspots” for having a markedly high number of threatened plant and animal species. Apparently, this is mainly due to (i) habitat loss as brought about by deforestation and increasing human encroachment on forested areas; and (ii) hunting and illegal poaching of wild animals from the forests. This present predicament has prompted various researchers involved