Effects of heavy grazing on invertebrate assemblages in the Succulent Karoo, South Africa

Invertebrate assemblages occurring on Paulshoek, a heavily grazed communal farm in Namaqualand, South Africa, were compared to those found on adjacent , moderately grazed farms. The study was conducted at three sites on the co mmunal farm, each bordering a different commercially managed farm. Results of pitfall trapping and Berger-Parker dominance indices showed that inverte brate abundance was consistently higher in the heavily grazed areas. Specie s richness was greater on the moderately grazed areas at two of the three s ites, while Shannon diversity was higher at all three moderately grazed loc alities. Cluster analysis, multidimensional scaling and ANOSIM (Analysis of Similarities) pointed to considerable differences in invertebrate assembla ges where habitat degradation was severe. Invertebrate diversity decreased sharply with decreasing total and perennial plant cover. Dominance indices, on the other hand, tended to increase in response to decreasing vegetation cover. Greater invertebrate abundance in severely degraded areas may compo und the effects of overgrazing, because further degradation of habitat may hinder recruitment by palatable perennials. (C) 1999 Academic Press.