Aspects of Ecology and Threats to the Habitats of Three Endemic Herpetofaunal Species on Negros and the Gigante islands, Philippines

Abstract

The nature of the microhabitats and the population 1 density of two endemic frogs (Plahjmantis spelaeus and P. insulatus) and one endemic gekkonid lizard (Gekko gigante) were studied in southwestern Negros Island and Gigante Islands in the Visayan Sea from January 2004 to March 2005. Platymantis spelaeus is found only in southwestern Negros Island. Platymantis insulatus and Gekko gigante are found only in the Gigante Islands in the Visayan Sea. The study used direct observations and the quadrat technique for population counts. Temperatures and relative humidity ranges in the general environment (limestone karst rainforest) and in the microhabitats (rock crevices, rock fissures, and caves) occupied by the three species were recorded. The population density of each of the three species was found to be more than the minimum viable or effective population size for long-term fitness. The two species on the Gigante Islands are limited in distribution to the study areas, hence could qualify under the conservation status of Endangered. However, because these island populations have apparently existed for millions of years, the appropriate status is Vulnerable. The temperatures in the microhabitats were stable, in the lower 20s°C, and the relative humidity ranges were 75-95%. The microhabitats ranged from moist to wet. The egg-laying sites of P. spelaeus (a direct developer needing moisture for reproduction) are apparently the deep rock crevices inside caves and those of G. gigante are the cave roofs. The main threats to the survival of the three species are direct human disturbance and reduced supply of water resulting from forest destruction and prolonged droughts.