Reproduction of wild Japanese macaque females of Yakushima and Kinkazan Islands: A preliminary report

Abstract

Wild Japanese macaque females of the Yakushima and Kinkazan populations exhibited similar reproductive features. (1) Births/female/year (BR: 0.27–0.35) was lower than those of provisioned troops, but (2) infant mortality (IM: 0.23–0.25) was higher than those of provisioned troops. (3) The interbirth interval (IBI) following the death of infants was 1.5–1.6 years, shorter than that following surviving infants (2.2–2.4 yrs). (4) Birth sex ratio (BSR) did not differ from 1∶1. There was no consistent correlation between (5) female age and IM, (6) maternal rank and offspring BSR, or (7) maternal rank and reproductive success. On the other hand, (8) BR of Yakushima females was significantly lower than that of Kinkazan females. In particular, (9) Yakushima females stopped reproduction earlier than Kinkazan females, although (10) the first birth of Yakushima females was about one year earlier than Kinkazan females. (11) BR exhibited a humped curve against female age in Yakushima, but it was uncertain whether old-aged females of Kinkazan exhibited a post-reproductive life span (PRLS). (12) The survivorship for female juveniles was lower than that for male juveniles in Yakushima, whereas the survivorship for male juveniles was lower than that for female juveniles in Kinkazan. These data may indicate that Yakushima females more severely compete for resources than Kinkazan females, because of high population density, whereas the population density of Kinkazan might be limited by climate (e.g. heavy snow) rather than density dependent ecological effects.