Variety among physical landscape features in natural grassland-plantation forestry mosaics promotes diverse butterfly assemblages

Abstract

Various physical landscape features across local and regional spatial scales contribute to heterogeneity. This means that ostensible maintenance of physical landscape features as representatives of heterogeneity (i.e., a meso-filter conservation approach) can contribute to conservation of insect assemblages. Using butterflies as model organisms, we investigate the conservation value of specific physical landscape feature types (rocky areas, wetlands, and gullies) relative to open grasslands, across 32 study sites in a natural grassland-plantation forestry mosaic in South Africa. We found that all considered landscape feature types had equal species richness and diversity levels compared to open grasslands. Yet, β-diversity (mostly accounted for by species turnover) was overall high between rocky areas, wetlands, and open grasslands, resulting from associations between some butterfly species and certain landscape feature types. Gullies were occupied by nested assemblages of rocky areas and open grasslands, suggesting that gullies have lower conservation importance, and should be targets for restoration. Topography and butterfly food plant availability further influenced β-diversity patterns and should also be considered when adopting a meso-filter conservation approach. β-diversity was also high among similar feature types, suggesting that a variety of landscape features that encapsulates environmental variation at a landscape scale can best conserve regional butterfly assemblages. While our focus was on butterflies, we anticipate these findings to be relevant to other insect groups, given that butterflies have successfully been used as conservation surrogates for other terrestrial insect taxa (e.g., grasshoppers) in the same area.