EFFECTS OF FOREST FRAGMENTATION ON CANOPY SPIDER COMMUNITIES IN SE-ASIAN RAIN FORESTS

摘要

Species diversity is by far highest in arthropods, and is in the tropics exceptionally high in the tree canopy. Until today canopy diversity has been neglected in research, however, so that the real impact of anthropogenic forest destruction on species diversity, as well as its functional importance can hardly be assessed. We collected canopy arthropods by insecticidal knockdown fogging in SE-Asian lowland rain forests between 1992 and 2001, and here we use spiders to investigate the consequences of slash-and-burn cultivation. We measured species diversity in a primary forest and in six forest fragments of different age and degree of isolation. Our statistical analysis suggests that neither year of sampling nor tree species significantly affected spider communities. By contrast, spider communities were clearly determined by forest isolation followed by forest age, both resulting in spicier communities specific to different forest types. In respect of guild composition, spider communities in the isolated forests were most clearly affected with the result that orb-web weavers had increased at the expense of sheet-web weavers, agile hunters, and cursorial hunters. Species richness was positively correlated with forest fragment age only under conditions where colonization was possible. In those gradient forests which adjoined primary forests, communities approximated those in the primary forest within 40 years. In contrast, a distance of 10 km effectively prevented re-immigration, resulting in low-diversity communities that showed hardly any development in 50 years. Our data suggest that most primary forest spiders are habitat specialists with restricted dispersal ability, indicating that the erosion of biodiversity can only be stopped by a high degree of habitat connectivity. Accepted 7 December 2010.