Effect of habitat transformation on dung beetle assemblages: A comparison between a South African nature reserve and neighboring farms

The effect of habitat transformation on dung beetle assemblages in the north-western Free State was investigated by comparing the fauna of a nature reserve with that on neighboring farms. Dung beetle sampling was done in four different localities within two different habitat types, a grassveld area and a bushveld (savanna) area. In these two habitat types, dung beetle assemblages in Sandveld Nature Reserve (27° 37′ S, 25° 46′ E) and on farms were compared. Eighty-three species belonging to 26 genera were captured in the study area. Doube’s classification was used to divide the dung beetles into functional groups according to the manner in which they use and disturb dung. The grassveld habitats were dominated by larger dung beetles belonging to functional groups I and II, whereas in the bushveld habitats smaller dung beetles belonging to functional groups IV and V were dominant. There were definite habitat preferences, with the larger dung beetles belonging to functional group I and II preferring the grassveld habitats and having higher abundance in the natural rather than the disturbed habitats. The smaller dung beetles, belonging to functional group V, preferred the bushveld habitats. The better competitors (the larger dung beetles) occurred more abundantly in the grassveld habitats and also more abundantly in the natural grassveld habitat than in the disturbed habitat. None of the indices measuring species richness nor dominance showed significant differences between the four habitats. The dung beetle assemblages in all four habitats showed a log series pattern, with high abundance of a few dominant, highly effective competitors and a large number of ‘rare’ species, which were assumed to be less effective competitors. This does not, however, imply that the dung beetles were similarly affected by the different habitats, because the biomass of dung beetles was higher in the grassveld than the bushveld habitats and also higher in the natural habitats. A change in vegetational ground cover caused by overgrazing and trampling has a greater effect on the larger, more effective competitors in the assemblage, whereas the smaller less effective competitors do not seem to be affected by this change.