Seasonal abundance and prey selection of the nymphs of three sympatric species of Sympetrum (Odonata: Libellulidae) in an intermittent pond

Odonates are obligate predators (Pritchard 1964), and the composition of their diet is reflective of their microhabitat and effectiveness in detecting and capturing prey (Griffiths 1973; Thompson 1978). In an intermittent woodland pond in southern Ontario, Canada, three species of Sympetrum (Odonata: Libellulidae) were found to coexist: S. internum Montgomery, S. costiferum (Hagen), and S. obtrusum (Hagen). Sympetrum species spend most of their life cycle in the aquatic stage and consume prey at all nymphal stadia (Pritchard 1964; Corbet 1999). They overwinter in the egg stage, hatch in early spring, and typically emerge in late June to late July (Walker and Corbet 1975). To better understand the role of coexisting Sympetrum nymphs in this intermittent pond environment, and to evaluate potential mechanisms behind their coexistence, we collected seasonal abundance and body size data for 2 years and analyzed gut contents of each species. In addition, we experimentally tested the prey selection and predatory rate of two different size classes of Sympetrum nymphs and two of their potential competitors, Lestes sp. (Odonata: Lestidae) and Acilius sp. (Coleoptera: Dytiscidae), in laboratory microcosms