Wide corridors with much environmental heterogeneity best conserve high dung beetle and ant diversity

Abstract

Landscape ecological networks (ENs) consist of landscape-scale conservation corridors that connect areas of high natural value within a production mosaic with protected areas (PAs). In South Africa, ENs have been implemented on a large spatial scale to offset the negative impacts of plantation forestry on indigenous grasslands. We focus on corridor width as a factor for conserving dung beetle and ant diversity within an EN. We also investigate the importance of natural environmental heterogeneity (elevation, vegetation type) and habitat quality (soil hardness, invasive alien plant density). We sampled dung beetles and ants in 30 corridors of different sizes, and at ten sites in a nearby PA. In addition, we also analysed dung beetles according to their feeding guild. Tunnelling dung beetle species richness increased with corridor width. Rolling dung beetle species richness was higher in the PA than in the corridors of the EN. The dung beetle assemblage within the EN differed from that within the PA. Corridors of various widths differed in ant composition but not in species richness. Furthermore, the PA and the EN differed in environmental variables, which contributed to differences in dung beetle species richness and assemblage composition. Within the EN, environmental heterogeneity across the landscape was more important than corridor width for driving species diversity of both dung beetles and ants. When planning future ENs, wide corridors (>280 m) that encompass as much natural heterogeneity across the landscape as possible will best conserve the range of local insect species.