Heterogeneity of dung beetle (Coleoptera: Scarabaeidae) assemblages in northern KwaZulu-Natal, South Africa: conservation implications

Abstract

Investigating the extent of local scale heterogeneity in assemblages is necessary to achieve a sound understanding of the processes giving rise to local assemblage patterns and the variation between them. Moreover, a clear understanding of local scale heterogeneity of assemblages is imperative in the development of effective regional conservation strategies. Previous studies examined the local scale heterogeneity in dung beetle assemblages between mixed woodland and sand forest habitats in Tembe Elephant Park, KwaZulu-Natal. Sand forest is an endangered habitat type in southern Africa which, when disturbed, opens up and changes towards mixed woodland. Reversion to the original sand forest structure after disturbance has never been recorded. Dung beetle assemblages were found to be homogenous within, but significantly heterogenous between, habitat types. It was therefore suggested that disturbance of sand forest (elephant foraging inside, and human occupation outside the Park) was likely to affect the assemblage structure of dung beetles in sand forest. Therefore, the aim of this study was to determine the effect of human- and elephant-induced disturbance on dung beetle assemblages in sand forest. Furthermore, disturbed sand forest dung beetle assemblages were predicted to be more similar to mixed woodland than to undisturbed sand forest assemblages. Disturbance by elephants causes sand forest vegetation structure to change to that of mixed woodland and this resulted in elephant-disturbed sand forest dung beetle assemblages becoming more similar to mixed woodland assemblages. Assemblages in human disturbed sand forest were unique and associated with human-related activities. The reliability and predictability of dung beetle indicator (species specific to a particular habitat type) and detector species (species indicative of the direction of habitat change) identified for Tembe in a previous study were tested. The results of this study largely supported the suite of bioindicator species first identified. Detector species were found to provide information complimentary to the indicator species and vegetation data available for sand forest. In addition, an identification key for the dung beetle species collected in Tembe Elephant Park to date was compiled. This key facilitates the use of dung beetle assemblages in indicator and monitoring systems in this reserve by providing a rapid and effective means of identifying the dung beetle species. The abundance-body size relationships of the dung beetle assemblages in mixed woodland, undisturbed and disturbed sand forests were also determined. Four hypotheses that account for the relationship between body size and abundance or its variants, were tested here, namely the energy equivalence rule, interspecific competition, differential extinction, and the biomass frequency distribution hypothesis. The disturbed sand forest assemblages were used to test whether disturbance alters the relationships between the macroecological variables (i.e. body size, abundance and biomass) and their interrelationships. This study provided some support for the biomass hypothesis. The major relationship between body size and abundance held despite human- and elephant-induced disturbance. Nonetheless, this study indicates that human- and elephant-induced disturbance alter sand forest dung beetle assemblages and may have significant implications for other taxa that occupy this endangered habitat type. Monitoring of the impacts of large herbivores on sand forest in reserves should thus be continued, and dung beetles provide one effective means by which this can be achieved.