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 fromcompetition in both within- and inter-troop contexts. The balance between these two formsof competition was analyzed from the behavioral and demographic data recorded for a wildpopulation of ring-tailed lemurs at Berenty Reserve, Madagascar. Within a troop, harsh andpersistent aggressive behavior (targeting behavior) among female members ultimately evictedsome victims. Troop size may infl uence the correlations between female rank and their reproductiveparameters. In large troops, lower ranked females tended to show lower reproductivesuccess than other females, but the differences were not significant. Birth rate and reproductivesuccess (number of surviving infants) exhibited a humped curve against troop size, corresponding to Wrangham's IGFC (inter-group feeding competition) hypothesis. A troopmay 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 eachfemale may decrease due to serious within-troop competition. Then, dominant females mayevict subordinate females from the troop. The evicted females may form a new troop (troopfi ssion), and transfer into other troops (i.e., female transfer/fusion), or die (group extinction).