Comparison of carabid beetle (Coleoptera: Carabidae) occurrence in rain forest and human-modified sites in south-eastern Madagascar

Abstract

High species diversity and endemism make Madagascar one of the world's biodiversity hot spots. However, forest cover and, thereby, biodiversity are decreasing rapidly due to human activities. Most of Madagascar is now covered by secondary vegetation, which is species-poor and contains many introduced species. In this study, the effect of human impact through alteration in vegetation on carabid beetles (Coleoptera: Carabidae) was assessed. The study was conducted in montane rain forest in the Parc National de Ranomafana (south-eastern Madagascar), and in a nearby village area with various types of secondary vegetation. Beetles were collected by hand and by pitfall traps from ten sites from both areas. A total of 246 specimens belonging to 54 species were collected. Pitfall traps yielded only six specimens, which clearly shows that pitfall trapping is not a feasible method for catching carabids in such habitats. From the forest in the national park, 38 species were collected and from the village area 28 species. Species compositions and the dominant species were different: 12 species were found from both areas, while 16 species were unique to the village area and 26 species were unique to the forest. Half of the species were singletons and three most abundant species formed 31% of the total number of individuals. We conclude that because forest-dwellers do not occur in the human-modified environment, such species are at great risk of becoming extinct if current rates of forest decline continue in Madagascar.