Effects of forest fragmentation on four Ctenus spider populations (Araneae: Ctenidae) in central Amazonia, Brazil

The effects of habitat fragmentation on four Ctenus spider populations in central Amazonia were investigated. Fourteen Ctenidae species were collected in nine forest fragments (<= 10 ha) and nine continuous forest sites (> 1000 ha). Four species, belonging to the genus Ctenus (C. amphora, C. crulsi, C. manauara and C. villasboast), were found in sufficient numbers to determine by covariance analyses, how isolation and litter depth affect their population densities. Litter depth did not affect spider densities, however, controlled experiments involving litter manipulation are more appropriate to test these relations. C. amphora and C. villasboasi presented much smaller populations in fragments, while C. manauara and C. crulsi apparently were not affected by forest fragmentation. On the other hand, the abundance of these species in the edges of fragments and continuous forest were similar, suggesting a decrease in the populations of C. amphora and C. villasboasi between 5 and 150 m from the edges. Thus, isolation and forest reduction increase the chances of local extinction and threaten the diversity of ctenid spiders.