Topographic heterogeneity plays a crucial role for grasshopper diversity in a southern African megabiodiversity hotspot

Abstract

Topographic heterogeneity as a determinant of insect diversity pattern has been little studied. Responses of grasshopper assemblages to three hill sizes were assessed in the arid Succulent Karoo, South Africa. This area is one of the world’s 25 hotspots for conservation priorities. Small hills overall were more speciose than medium or large hills. There were also significantly higher densities of small-sized grasshoppers on small hills than on medium or large ones. The slopes of the three hill sizes did not differ significantly either in their species richness or abundance, and there was no significant difference in species richness between summits only of the three hill sizes. Patterns of grasshopper species dominance were markedly variable among sites, but with clear differences between small and larger hills, associated with vegetation characteristics. Vegetation cover and grass cover was less on the small hills. Grasshopper taxonomic groups varied among the three hill sizes, with small hills being taxonomically more diverse, supporting species from four families and nine subfamilies, while medium and large hills only supported Acrididae. It is concluded that topography has a remarkably strong effect on various aspects of grasshopper spatial heterogeneity and that small hills in particular are a major factor to consider in spatial conservation planning.