Distance-driven species turnover in Bornean rainforests: homogeneity and heterogeneity in primary and post-logging forests

Selective logging is practiced extensively within tropical rainforests of south-east Asia, and its impact on local biodiversity is well documented. Little is known, however, about the impact of selective logging on patterns of spatial heterogeneity of species. We set out to test the hypothesis that selective logging will lead to a homogenization of the associated faunal assemblages, using moths (Lepidoptera) as our subject taxa. Large-scale transects were established within primary and post-logging lowland mixed dipterocarp rainforests around the Danum Valley Conservation Area and surroundings, Sabah, Malaysia (4 degrees 50N5 degrees 00N and 117 degrees 35E117 degrees 45E). Five study sites were located within each habitat with geometrically increasing inter-site distances. Macro-moths plus Pyraloidea were sampled by light trapping in 2007 and 2008. Vegetation state was also measured at each site. A clear distancedecay relationship (decreasing assemblage similarity with increasing geographic distances) was observed in primary forest but was absent in the post-logging forest. Large, comparable numbers of macro-moth species were found in both primary and post-logging forests. There were no significant differences in moth assemblage composition between primary and post-logging forests. There are important structural differences between primary and post-logging forests reflected in the moth assemblages. A two-stage hypothesis combining both neutral and niche concepts is probably the most parsimonious explanation of these results. First, the composition of the moth assemblage is almost certainly determined locally by the variety of planthosts available to larvae, with the plants representing important niche dimensions for the moth species. Second the turnover (or lack of same) in the underlying plant assemblage probably reflects clumping and, in turn, dispersal capacity of the commoner plants in each forest type. Although the impact of selective logging may be subtle, this study suggests that selective logging results in the spatial homogenization of macro-moth assemblages.