Amphibians and reptiles in tropical rainforest fragments on Negros Island, the Philippines

To elucidate effects of fragmentation and degradation of tropical rainforest on Negros Island (Philippines) on tropical herpetofauna, nine tropical rainforest fragments (eight limestone and one non-limestone), ranging in area from five to 122 ha (total area = 352 ha) in south-western Negros were surveyed using cruising and quadrat sampling methods, between December 2001 and October 2002. A 14-ha limestone plantation forest served as a reference site. Ten to fifteen of the total 61 species (16.4-24.6%) expected in the nine forest fragments (taken as a whole) had been lost in the previous 50 years. These species are known to occur in the tropical rainforest on Cuernos de Negros and environs in south-eastern Negros Island at altitudes <500m above sea level. The factors responsible for the loss of these species appear to be (1) removal of large trees, which decreases canopy cover causing physical changes; and (2) forest fragmentation, which increases the edge areas. However, it is not possible to separate the effects of each of these two factors. The main factor that was correlated with the number of species in the limestone forest fragments appeared to be area. Two species of frogs appeared to be represented by relatively moderate population densities: the Negros cave frog (Platymantis spelaeus) and the common forest frog (Platymantis dorsalis). The burrowing skink (Brachymeles boulengeri taylori) also exhibited a relatively higher density than the other burrowing species of skinks. The other herpetofaunal species exhibited low population densities.