Edge effects of oil palm plantations on tropical anuran communities in Borneo

The expansion of industrial agriculture (oil palm) has significantly reduced lowland tropical diversity through direct loss or alteration of habitat, leading to habitat fragmentation and edge effects. Edge effects can have serious impacts on species diversity and community dynamics. To assess the effect of oil palm plantation edges on anuran communities in Sabah, Malaysian Borneo, we surveyed anuran species and measured structural habitat and landscape parameters at 74 sites spread across forest and plantation habitats along the Kinabatangan River. We then evaluated how anuran species richness and assemblage composition varied in relation to these environmental parameters. Relative species richness was higher at forest sites, compared to oil palm plantation sites. Plantation sites were dominated by wide-ranging terrestrial species, and assemblage composition varied mostly in relation to standing surface water. Forest habitats supported both more endemic and arboreal species. Variability on anuran assemblage composition in forest habitats was greatest in relation to distance to forest edge followed by canopy density, which was also partially correlated with forest edge distance. Moreover, anuran species richness in forest habitats declined as proximity to the forest-plantation interface increased, and as canopy density decreased. Our study provides further evidence that oil palm plantations provide little conservation benefit to anurans. Furthermore, oil palm plantations appear to have adverse pervasive impacts on amphibian diversity considerable distances into adjacent forest areas. These findings suggest that in order for small patches or narrow corridors of retained forest in landscapes managed for oil palm to maintain biodiversity values in the long term, their sizes and widths need to adequately account for the considerable influence of edge effects.