DOES TROOP SIZE OF WILD JAPANESE MACAQUES INFLUENCE BIRTH-RATE AND INFANT-MORTALITY IN THE ABSENCE OF PREDATORS

For the wild Japanese macaques of Yakushima and Kinkazan Islands, we a nalyzed the relationship between the troop size or the number of adult females of each troop, infant/adult female ratio (IFR; crude birth ra te), and infant mortality (IM) in habitats with no predators. In Yakus hima, IFR was positively correlated to troop size and the number of ad ult females. In Kinkazan, however, IFR tended to decrease with the num ber of adult females. This difference may be due to the difference in troop size; i.e. in Yakushima, where troop size was small, IFR may inc rease with that of troop size, because a relatively larger troop is li kely to the advantage in intertroop competition. In Kinkazan, where tr oop size was large, however, IFR is likely to decrease with troop size , because intratroop competition may increase. Thus, the present data roughly support WRANGHAM's model of the social structure of female-bon ded primates, and suggests that there is an optimal troop size for bir th rate (BR). On the other hand, there was no clear correlation betwee n IM and the troop size or number of adult females of each troop.