The value of forest fragments for maintaining amphibian diversity in Madagascar

Abstract Forest fragmentation often causes biodiversity loss, but there is no consistent pattern on species' reactions. Considering the alarming rate of deforestation in the tropics, and the fact, that large areas of protected continuous forest are limited, it becomes increasingly important to determine the biodiversity value of fragmented forests. In order to investigate fragmentation effects on rainforest frogs in Madagascar and to assess the conservation value of these fragments, we analyzed amphibian diversity in a continuous rainforest and nearby forest fragments. We hypothesized that species richness is lower in fragments compared to continuous forest, and that fragmentation leads to altered assemblage composition. We found no fragmentation effects on species richness, demonstrating that fragments may maintain local species richness comparable to continuous forest. The presence of streams was the most important factor for high species richness, independent of fragmentation status. However, we detected fragmentation effects on species composition. As expected, several species were restricted to continuous forest, but many species occurred in both forest types, and some species were only found in fragments. Rainforest amphibians in our study area were less sensitive to fragmentation than expected. Adaptations to natural disturbances like cyclones could be one reason to explain this. However, as some species exclusively occurred in continuous forest and species composition differed between continuous forest and fragments, we conclude that fragments cannot substitute continuous forest blocs, but are generally important for maintaining amphibian diversity in Madagascar, especially if they comprise streams. Forest fragments should hence be included in conservation planning.