INTER- AND WITHIN-TROOP COMPETITION OF FEMALE RING-TAILED LEMURS: A PRELIMINARY REPORT

Abstract

In a female-bonded/matrilineal group of primates, females may suffer from competition in both within- and inter-troop contexts. The balance between these two forms of competition was analyzed from the behavioral and demographic data recorded for a wild population of ring-tailed lemurs at Berenty Reserve, Madagascar. Within a troop, harsh and persistent aggressive behavior (targeting behavior) among female members ultimately evicted some victims. Troop size may infl uence the correlations between female rank and their repro- ductive parameters. In large troops, lower ranked females tended to show lower reproductive success than other females, but the differences were not significant. Birth rate and repro- ductive success (number of surviving infants) exhibited a humped curve against troop size, corresponding to Wrangham's IGFC (inter-group feeding competition) hypothesis. A troop may show the following cycle: First, a troop gains advantages via inter-troop competition, and increases in size. When optimal troop size is exceeded, the reproductive success of each female may decrease due to serious within-troop competition. Then, dominant females may evict subordinate females from the troop. The evicted females may form a new troop (troop fi ssion), and transfer into other troops (i.e., female transfer/fusion), or die (group extinction).