Effects of rainforest fragmentation and correlates of local extinction in a herpetofauna from Madagascar

Abstract

Habitat destruction in tropical forests often produces fragmented landscapes where relatively small forest remnants are present in a human-dominated matrix. To estimate rates of species loss after fragmentation and identify the traits of species which are most vulnerable to extinction, we assessed the distribution of amphibians and reptiles in an old (>50 yr) fragmented landscape in southeastern Madagascar. In the six rainforest fragments (10-457 ha) surveyed between 1999 and 2002, we detected forty-five species (28 reptiles, 17 amphibians). These species were not distributed randomly among the fragments but rather were very highly nested. The herpetofauna of small fragments consisted of smaller subsets of the species pool found in larger fragments. Species loss rates were high, with up to 64% of reptile and 88% of amphibian species lost when compared to the largest fragment. Species that were particularly prone to local extinction were generally rare, habitat specialists, and/or intolerant of the matrix habitat. Edge-avoidance was a good predictor of extinction vulnerability for frogs, but not for reptiles. Body size was generally not a good predictor of extinction proneness. In contrast with some other studies of amphibians and reptiles in fragmented landscapes, the results of this study indicate that species loss is a likely consequence of persistent isolation.