Overlap at landmarks by lek-territorial and swarming males of two sympatric polistine wasps (Hymenoptera Vespidae).

A mark-recapture study revealed that, in September and October, males of two Polistes species share the same trees and electricity poles: P. dominulus defend small fixed territories (an alternative strategy is flying through several territories), while P. gallicus patrol numerous landmarks in swarms, returning to the same collective perches day after day. This species-specific difference in spatial behaviour (but not in site-attachment), confirmed by laboratory experiments, is associated with higher P. gallicus density at landmarks over a shorter activity period. 2. The aggressive, territorial, P. dominulus males direct repeated attacks towards the swarming P. gallicus, which show weaker aggressive displays. The greater number of P. gallicus leads to a reduction in territory size followed by displacement at landmarks of P. dominulus, both in the field and in captivity. Interspecific competition around vertical silhouettes is reduced by a partial shift in seasonal activity, variation in the territorial habits of P. dominulus males, divergent preferences inside the same landmarks systems, and different settlement rules (resident versus mobile males). 3. The difficulty in monopolizating female groups and the proximity of landmarks to resources may explain the overlap at the same display sites. Both species were able to discriminate between conspecific and heterospecific females when tested in double choice trials at habitual perches, where most natural copulations were observed. The higher «mistake» rate in P. gallicus males than in P. dominulus is consistent with their different mating systems (scramble competition polygyny in the former species, lek polygyny in the latter).