Conserving dragonfly (odonata) assemblages relative to river dynamics in an African savanna game reserve

Abstract

Adult male dragonflies were sampled from 42 sites on four variously disturbed rivers and three reservoirs in Kruger National Park, South Africa. Fifty-one species and 2671 individuals were recorded. Large flow fluctuations resulted in a high species turnover during sampling. Dragonfly species richness mostly conformed with the intermediate-disturbance hypothesis, with species richness high on the rivers with moderate disturbance and low on the most disturbed ones. Ordination of dragonfly species data separated rivers into clear groups, indicating that the dragonfly assemblages reflected the distinct plant physiognomic and physical environmental conditions of each river system. Species that were abundant on any particular river had biotope preferences that reflected the overall environmental conditions of that river. Aquatic macrophytes, including two exotic invasive species, promoted dragonfly species richness. These species, however, were not rare or threatened. Highly disturbed rivers were characterized by species that preferred highly exposed situations with broad environmental conditions. In contrast, long grass or shady trees were important for some species because they buffered larger-scale, unpredictable environmental changes. Biotic disturbance was also important because trampling by buffalo reduced local species richness and composition. Dragonfly assemblages were highly visible and sensitive indicators of aspects of long-term environmental conditions of the water body. Management recommendations for dragonflies and other aquatic invertebrates include maintaining water and riparian biotope heterogeneity, maintaining constant flow rates and water levels, and allowing some macrophyte cover. A little natural and anthropogenic disturbance encourages much greater species richness than more extreme disturbance. The Sable River is a major subject for conservation action in the premier protected area of Kruger National Park.