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

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)

DO RINGTAILED LEMURS EXHIBIT A SKEWED BIRTH SEX RATIO DEPENDING ON SOCIAL AND ENVIRONMENTAL CONDITIONS? A PRELIMINARY ANALYSIS OF A WILD POPULATION

In a 13-year study, we examined the birth sex ratio (BSR) of wild ringtailed lemurs at Berenty Reserve in Madagascar. Their BSR represented an equal sex ratio at the population level, irrespective of population change. High-ranking females did not always overproduce sons or daughters. In newly formed groups, females did not always overproduce daughters, and the BSR of young females was similar to an equal sex ratio. Thus, our data do not support the Trivers–Willard, local resource competition–population, or local resource enhancement hypotheses. Only one significant skewed BSR was observed: low-ranking females in medium-sized groups overproduced sons. This finding may support the local resource competition–individual hypothesis, but does not do so robustly

DECREASE IN THE BODY MASS OF WILD RINGTAILED LEMURS AT BERENTY RESERVE IN MADAGASCAR WITH ENVIRONMENTAL CHANGES

We measured the body mass of 76 (in 2006) and 73 (in 2011) wild ringtailed lemurs (Lemur catta) inhabiting the Berenty Reserve in Madagascar. Compared with the data recorded in 1999 (Koyama et al., 2008), the mean body mass of the adults had decreased significantly. In 2006, the adult females had decreased from 2.27 kg to 1.98 kg, and the adult males from 2.22 kg to 2.03 kg. In 2011, the body mass of both adult males and females was still 1.99 kg. In 2011, the group variations in body mass may have expanded. No sexual difference was observed in body mass, similar to the data from 1999. Despite their reduced body mass, adult females maintained a high birth rate (73.0% annually), but infant mortality was very high (86.2%) from 2006 to 2011. We discuss these phenomena with reference to environmental changes in this reserve