Annual variation in the mating system of the dragonfly Paltothemis Kneatipes (Anisoptera: Libellulidae)

The libellulid dragonfly Paltothemis lineatipes exhibits annual variation in male mate-locating behaviour, variation that appears to be related to changes in the number of males competing in an area. In a year when males were numerous, as reflected in a high rate of male-male interactions, individuals defended small streamside territories, regularly raided neighbouring territories in an attempt to steal females there, and often were forced off their territory after a few hours of daily ownership. In this year, temporal partitioning of a given site was common, with the same males taking it in turns to defend the location for part of each day. In a year when males were much less numerous, as seen in a very reduced rate of aggressive encounters, males defended territories more than twice as large on average than in the high-density year; they rarely took females from neighbours, and they much less frequently 'shared' ownership of a site with another male on a given day. The changes between low- and high-density years were not associated with a change in average daily copulatory success of territorial males, although the variance in mating success was significantly greater in the high-density year.