Impacts of selective logging on tropical butterflies in Sabah, Malaysia

Abstract

This study investigated the impacts of selective logging on tropical butterflies in the lowland dipterocarp rainforest of Sabah (Malaysia, Borneo). Walk and point-count transect methods were used to survey butterflies in unlogged forest and forest that had been selectively logged 10-11 years previously. The study focused on butterflies in the sub-families satyrinae and morphinae (Nymphalidae) and the family Riodinidae. A total of 1825 adult butterflies was recorded from 34 species at 80 observation stations on 8km transects repeated four times per month for a period of one year (March 1999—February 2000). Most of the butterfly species that were present in the unlogged forest were also present in logged forest. There was little difference in numbers of individuals or numbers of species recorded in logged and unlogged forest. However Shannon- Wiener and Simpson's diversity indices (species evenness) were significantly higher in unlogged forest than the logged forest, although there was no difference in Margalef's index (species richness). These results show that selective logging affected species evenness of tropical butterflies more than species richness. Vegetation structure in logged forest was significantly different from that in unlogged forest >10 years after logging. However changes in vegetation structure were only weakly related to butterfly diversity. There was no strong evidence that selective logging contributed to the loss of butterfly species with more restricted geographical distributions. Seasonal effects in terms of monthly rainfall did not relate to seasonal changes in diversity of butterflies, but there was a relationship with sunshine. Fruit-baited traps were used to investigate vertical stratification of butterflies in unlogged forest from ground to canopy levels. A total of 542 individuals from 40 species were captured in traps. Low-level (2m) traps caught species with more restricted distributions than medium-level (20m) or high-level (40m) traps (31, 19 and 12 species repectively). Adult longevity showed that individuals could survive up to 164 days. Movement of butterflies between traps at different heights was relatively low. Data from traps confirmed that species of satyrinae can be recorded reliably using ground-based transect techniques.