The impact of landuse on invertebrate assemblages in the Succulent Karoo, South Africa

[摘要] The Succulent Karoo biodiversity hotspot is threatened by pressure caused by increasinghuman populations and its associated land use types. Land use is primarily focussed onagriculture, with livestock grazing as a dominant land use in the region. Cultivation isalso practiced along the major perennial rivers, and in drier areas, where this largelydepends on rainfall. Only about seven percent of the biome is formally protected, and thisarea substantially under-represents the biodiversity of the Succulent Karoo and does notincorporate key ecological processes and biodiversity drivers. Therefore, there is urgentneed for outside reserve conservation initiatives, whose success depend on understandingthe ecosystem function of the Succulent Karoo. This study aimed to determine theimpacts of heavy grazing, light grazing and cultivation (in a 30-year old fallow field) onassemblages of ground-dwelling and flying invertebrates. Seasonal assemblage changeswere also determined. Vegetation structure and composition were determined using theline-intercept method to determine if vegetation patterns explain patterns in invertebrateassemblages. Abandoned fields harbour the lowest number of plant species, and thesetogether with the heavily grazed sizes are dominated by a high cover of Galenia africana(Aizoaceae). Lightly grazed sites have the highest structural complexity, with a highcover of succulents and non-succulent perennials. After the winter rains, annual plantsoccupy most of the bare ground in heavily grazed and previously cultivated sites.Seasonal changes in assemblages of ground-dwelling and flying invertebrates weredetermined by sampling during the four seasons at the same localities. Results of pitfalltraps sampling for ground-dwelling invertebrates and coloured pan traps for flyinginvertebrates showed that overall species richness and diversity peaked in spring forflying invertebrates while peaks in richness for ground-dwelling invertebrates were insummer, with no difference in overall diversity. Overall abundance for ground-dwellinginvertebrates was highest in summer and lowest in winter. Ground-dwelling invertebratefauna was dominated by Formicidae and Araneae. Grazing and cultivation lead to skewedcommunity composition of ground-dwelling invertebrates which favours disturbancetolerant and generalist species such as Anoplolepis steingroeveri (Forel).

[发布机构] Stellenbosch University