Aggregation during oviposition and predation risk in Sympetrum vulgatum L. (Odonata: Libellulidae)

Summary

Tandem pairs of the libellulid dragonfly Sympetrum vulgatum always start oviposition with contact guarding directly over the surface of shallow water, where they are exposed to green frogs (Rana esculenta). Tandems which approached locations with other pairs already present started oviposition nearby regardless of whether or not predators were actually present. With predators present attack rates during arrival were lower on tandem pairs in groups than on pairs that oviposited alone. During oviposition the attack rate on groups was similar to that on solitary pairs, but predation risk to individual tandem pairs was lower due to dilution effects. Predation risk during tandem oviposition was similar for both sexes, but females had a higher risk of falling prey to frogs during post-tandem oviposition than males. If tandems were attacked by frogs, females left the site after tandem oviposition despite the male hovering above her, and the frequency of non-contact guarded post-tandem ovipositions was reduced.