Plantgemeenskappe en hulle geassosieerde epigeale en epifitiese invertebrate in 'n weidingsgebied in die Potchefstroom-omgewing

Abstract

Ecological models for rangeland management are limited by the lack of representative knowledge of the invertebrate communities in the South African grassland . The aim of this study was to investigate the vegetation and its associated epigeic and epiphytic invertebrates in a natural rangeland in the Potchefstroom district. The total composition of the epigeic and epiphytic invertebrates which was estimated by means of surveys is described to serve as a basis for future research in the grassland biome. It was established that changes in the composition of t he invertebrate community did occur within a year cycle and that such changes should be taken into account in research on invertebrate plant associations. Direct relationships between climatic changes and / or biotic factors and the species composition of the invertebrate community were difficult to ascertain. Phenological changes in the vegetation resulted in a higher diversity of microhabitats in the same area at different times of the year. Significant correlations and response of invertebrates to differences in the vegetation were found. A high vegetative biodiversity in the study plots was accompanied by a high biodiversity and species richness of invertebrates. Some Hemiptera species were associated with overgrazed patches in the rangeland which were caused by sheep and which were dominated by Aristida congesta, an increaser IV grass species. There was a lack of associations for most of the Coleoptera and Lepidoptera species with the dominant vegetation (Poaceae) while more phytophagous Coleoptera and Lepidoptera species were observed to feed on plant species not belonging to the Poaceae. Results on the distribution of some ant species showed that simple plant-insect relationships can be limited as parameters for environmental changes, though the habitat requirements of these ant species could not be fully established. A more synecological approach should therefore be adopted and complemented by the necessary autecological studies on invertebrates in South African grasslands. Many recommendations for relevant follow-up research were the outcome of this study. Multi variate analytical techniques proved to be a useful aid to investigate the associations of invertebrates and plants on a community level. The need for a more extended taxonomic service to identify the invertebrate morphospecies to a generic- and specific level in South Africa became evident during this study. A better knowledge of associations between invertebrates, vegetation and habitats can be applied to the management of natural resources. Applications include more sophisticated rangeland management, the conservation of endangered species as well as biodiversity, rehabilitation of environments, the identification of indicator species and a better understanding of ecosystem dynamics and in the final analysis the biogeography of invertebrates.