INFLUENCES ON VARIATION IN TERRITORIAL TENURES OF MALE WHITE-FACED DRAGONFLIES (LEUCORRHINIA-INTACTA) (ODONATA, LIBELLULIDAE)

Some individuals in species with extended periods of territorial occup ancy may change territory locations within a single bout of territoria l activity. Length of occupancy of mating territories among males in a local population of white-faced dragonflies (Leucorrhinia intacta) va ried from more than 6 h to 15 min or less. Males with short tenures of ten established territories in several locations on the pond during a day. Several hypotheses have been proposed to explain shifting territo rial sites rather than remaining in a single sire during one bout of t erritoriality. We attempted to test the hypothesis that males shift to leave low-quality sites. Site quality may be affected by costs of def ense in relation to intruder rate and the mating benefits of holding t he territory. To test whether variation in these possible effects of b enefits and costs of territoriality influenced tenure, we manipulated local quality of oviposition substrate and perch density. The quality of oviposition substrate, but not perch density, influenced both poten tial benefits and costs of territoriality. Female density was higher i n areas with good substrate, but so were rates of males intruding into the territories, rates of chasing by territorial males, and local den sity of territorial males. More matings occurred in areas with good su bstrate, but among males with tenures of 15 min or more, mating succes s per male and tenure lengths did not differ statistically among treat ments. Defense costs were low for all treatments and perhaps were not an important influence on tenure duration. Territorial males in this p opulation probably adjusted local density to expected mating success b y initial choice of site rather than by varying tenure length. Variati on in tenure length at a site resulted, in parr, from stochastic exter nal factors, such as predation attempts.