Grasshopper assemblage response to surface rockiness in Afro- montane grasslands

Grasshoppers are often an important functional component of ecosystems, and many species show high levels of endemism. Evidence exists that percentage surface rock cover within a landscape can predict diversity of grasshopper species. Nevertheless, the reason why grasshopper species are responding to rocky landscapes has not been established. Here, we explore whether grasshoppers are responding to physical rockiness per se, or rather to specific correlates of higher surface rock exposure within a landscape. We also determine if this response varies between grasshopper taxonomic groups. We sampled grasshoppers in Afro-montane grasslands in KwaZulu-Natal, South Africa, and recorded 10 environmental variables. We explored the influence of these variables on grasshopper community composition and grasshopper family composition. We also determined the vegetation characteristics, which significantly correlate with percentage surface rock cover in this landscape (geophyte richness, perennial grass richness and vegetation density), and then measured the similarity of species composition across these correlates. Overall, grasshopper assemblage composition, as well as familial composition, responded strongly to an elevation gradient, and not to the correlates of surface rock cover. In turn, the higher species richness in such areas is more likely a function of the significant vegetation correlates of higher surface rock cover. Across taxonomic groups, there are specialist species within each group which are associated with environmental conditions related to surface rockiness through its underlying correlates. Rock exposure across this grassland landscape is therefore an important contributor to grasshopper dispersion patterns, and has important implications for conservation planning for this taxon.