|Kuppler, J; Fricke, J; Hemp, C; Steffan-Dewenter, I; Peters, M: Conversion of savannah habitats to small-scale agriculture and its effects on grasshopper communities at Mt. Kilimanjaro, Tanzania, Journal of Insect Conservation, Springer, 19(3), 509-518 (2015), doi:10.1007/s10841-015-9772-7 [Link]|
About 20 % of the natural grasslands in Sub-Saharan Africa have been converted to cropland and 80 % of the converted area is managed by small-scale farmers. Despite the large contribution of small-scale subsistence farming to agricultural expansion in Sub-Saharan Africa only few studies investigated the effects on insect biodiversity. We studied the effects of the conversion of savannah to small-scale extensively managed ruderal areas and corn fields on grasshopper communities (Orthoptera: Caelifera). The study was conducted on the eastern slopes of Mount Kilimanjaro, Tanzania. Three plots per land use type were established and grasshoppers were repeatedly collected between September and December 2010 using standardized transect walk methods. In comparison to the natural savannah, cornfields exhibited lower numbers and densities of grasshopper species, while ruderal areas exhibited similar species richness. However, vegetation cover was the best predictor for species richness, with the number of grasshopper species nearly doubling from plots with scarce vegetation to those with a dense grass cover. The composition of grasshopper communities differed between land use types and vegetation cover, with habitat generalists being scarce. Therefore, the species richness of all land use types combined was considerably higher than the richness of single land use types. We found no rare or threatened species during sampling. Our study suggests that a mosaic agricultural landscape with areas of savannah and extensively managed ruderal areas may maintain a high biodiversity of grasshoppers. However, the effectiveness of such mosaics is strongly dependent on extensive farm management practises which retain significant amounts of grass cover throughout the year.