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 communal farm, each bordering a different commercially managed farm. Results of pitfall trapping and Berger–Parker dominance indices showed that invertebrate abundance was consistently higher in the heavily grazed areas. Species richness was greater on the moderately grazed areas at two of the three sites, while Shannon diversity was higher at all three moderately grazed localities. Cluster analysis, multidimensional scaling and ANOSIM (Analysis of Similarities) pointed to considerable differences in invertebrate assemblages 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 compound the effects of overgrazing, because further degradation of habitat may hinder recruitment by palatable perennials