a1 Museo regionale di Scienze naturali, Division of Zoology, via G. Giolitti 36, 10123 Turin, Italy and Parc Botanique et Zoologique de Tsimbazaza, BP 4096, Antananarivo 101, Madagascar.
Surveys of the amphibians (Order: Anura) of Ranomafana National Park, a midaltitude rainforest in central-eastern Madagascar, and nearby areas of disturbed habitats were carried out in two seasons (December 1991 and August 1992). A total of 40 frog species was recorded. In undisturbed areas many strictly terrestrial species were present, most of them belonging to the endemic family Mantellidae. These species showed changes in abundance between August and December, probably due to temperature variation. In contrast, most of the species found in altered habitats were arboreal or semiarboreal. These are ‘ecologically opportunistic’ species, not so sensitive to habitat variations and able to reproduce whenever conditions are favourable. These species were equally abundant in December and August and they appear to be able to live in a more varied habitat patchwork. To preserve the diversity and abundance of amphibians, nature reserves should retain a central core of primary forest to ensure the survival of the more specialized species, surrounded by a buffer zone of degraded vegetation to sustain the presence of more adaptable frog species.