Determinants of adult dragonfly assemblage patterns at new ponds in South Africa

Adult Odonata species assemblage patterns were studied at 8 ponds near Pietermaritzburg, South Africa. Different ponds had different assemblages. Strong inferential evidence from multivariate analysis and correlation suggested that the main determinants of assemblage patterns were certain biotic and abiotic environmental variables. In other words, assembly ‘rules’ may be governed more by factors external to the taxon than by interspecific competition. Larger ponds were not necessarily richer in species than smaller ponds because factors such as water quality, vegetation type and microsite diversity overrode biotope size. Species richness was greatest at shallow, well-vegetated ponds with clear, oxygenated water. Such ponds provide suitable conditions for both larvae and adults. Sunlight/shade and marginal/submerged vegetation gradients were the main drivers of assembly patterns at the ponds. Species assemblage patterns were determined by several variables acting together. In turn, the assemblage patterns at each pond were influenced by different variables representing different ecological successional stages.