Effects of rain forest logging on species richness and assemblage composition of small mammals in Southeast Asia

Aim The effects of logging and habitat degradation on the richness and abundance of small mammals in Asian rain forests are largely unknown. This work compares the species richness, dominance and evenness of small non-volant mammals between logged and unlogged forests, and assesses whether assemblage variability (beta-diversity) is similar between forest types. Location Southeast Asia, northern Borneo (Sabah, Malaysia), Sunda-shelf. Methods We surveyed species-rich assemblages of small non-volant mammals in three unlogged and three logged forests for 2 years. At each forest site, we sampled a permanently marked transect and two additional sites in three trapping sessions. All analyses were performed at both levels to include the effects of local abundances and point estimates, separately from the relative abundances of species on a more regional scale. Results We trapped a total of 1218 individuals of 28 species. Eleven common species accounted for 95% of all captures. Species richness and diversity were significantly higher in unlogged forest (27 species) than in logged forest (17 species). This was mainly attributable to the smaller number of rarely recorded species in logged forest (five compared with 16 in unlogged forest, with a total of fewer than 10 captures). However, all common species were present in both logged and unlogged forests, and our analyses revealed similar patterns of dominance, evenness and fluctuations in abundance. Hence overall assemblage composition in multivariate space did not differ greatly between forest types. Assemblages of Muridae and Tupaiidae showed similar population fluctuations in space and time, indicating that the ecology of these taxa may be partially driven by the same environmental factors. Main conclusions Although species were distributed patchily within sites, analyses at local and regional scales revealed similar patterns in diversity and assemblage variability, suggesting that effects of forest modification did not differ extensively locally and regionally, but had a profound effect on rare species. Our results emphasize the importance and conservation value of logged forest stands that are able to hold a large proportion of the small mammals also found in unlogged forests. Rare and more specialized species are more vulnerable to forest degradation than commonly caught species, resulting in the complete loss, or a decrease in numbers, of certain groups, such as arboreal small mammals and Viverridae.