Aggregating behavior during oviposition in the dragonfly Sympetrum vicinum (Hagen) (Odonata: Libellulidae)

This study examined the adaptive significance of ovipositing near conspecifics by pairs of the dragonfly Sympetrum vicinum. Studies were conducted at two artificial ponds in New York using a series of 1 m(2) plots along their shorelines. Although the majority of pairs oviposited alone, pairs also tolerated the presence of others only 5-10 cm away, and sometimes 2-7 pairs oviposited together within a single plot. Habitat selection (preference for certain plots over others) partially accounted for such behavior. However, where adjoining plots were homogeneous (i.e., used equally for oviposition), newly arriving pairs were more likely to begin dipping in a plot in which one or more pairs were already present, thus also suggesting mutual attraction among pairs. Oviposition efficiency (measured as no. abdominal dips/s) was apparently not compromised by ovipositing near conspecifics. Harassment from unpaired males had little effect on oviposition since unpaired males were uncommon and rarely approached pairs. However, lone pairs were attacked relatively more frequently by frogs than were pairs present simultaneously in die same plot. Although none of the 112 predation attempts I recorded were successful, frog attacks forced pairs to change sites, thereby lengthening the time required for oviposition. The absence of frogs or frog attacks at a site provided favorable conditions for pails to accumulate at a site; thus the presence of conspecifics may have signaled a safe area for oviposition.