Shinichi Yoshihiro

Environmental determinants of the altitudinal variations in relative group densities of Japanese macaques on Yakushima

Altitudinal variations in relative group densities of the Japanese macaques on Yakushima were studied. This is an ideal place for studying resource limitations because it avoids various complicating factors that are difficult to quantify but might affect animal densities, such as predation, interspecific competition, and past catastrophes. The relative group density was high in the coastal forest (0–400 m), while it did not differ among the higher zones (400–800, 800–1200 and 1200–1886 m). To examine this variation, three habitat variables were analyzed: total basal area of food trees per unit area, seasonal variations in fruit abundance, and total annual fleshy fruit production. All of these variables indicate that fruit and seeds are most available in the coastal forest. Thus, altitudinal variations in the density of Japanese macaques on Yakushima are determined by the total annual food abundance.

Vertical Distribution of Wild Yakushima Macaques (Macaca fuscata yakui) in the Western Area of Yakushima Island, Japan : Preliminary Report

A census of wild Yakushima macaques (Macaca fuscata yakui) was carried out in a 23-km2 area of the western coast of Yakushima Island, Japan. We analyzed the census data to investigate changes in monkey distribution associated with the vertical distribution of vegetation. In the lowland coastal zone of 0–300 m above sea level (a.s.l.), 4.8 troops and 62.4–99.8 monkeys are estimated to have existed per km2. In the mountainside zones of 300–900 m a.s.l., the troop density decreased to 1.3–1.6 troops/km2. Since there was no difference in size between the coastal and mountainside troops, population density should decrease with altitude to about 30–36 monkeys per km2. On the other hand, 2.4 troops and about 36 monkeys were estimated to have inhabited per km2 in the mountain summit zone of 900–1,323 m a.s.l.

A cytogenetic study on congenital limb malformations in the Japanese monkey (Macaca fuscata)

A cytogenetic investigation was performed on 88 Japanese monkeys (Macaca fuscata) with abnormal limbs from 11 free-ranging provisioned troops including nine individuals with abnormalities indistinguishable as to whether they were congenital or injurious. All of the monkeys with abnormal limbs including the nine questionable individuals had the same karyotypes as those of normal individuals. The chromosome number was 42, consisting of 20 bi-arm autosome pairs and a submetacentric X-chromosome and Y-chromosome. The ninth chromosome pair, which was the only chromosome pair with remarkable secondary constriction, displayed length polymorphism of the centromeric C-band and secondary constriction in both deformed and normal monkeys. These kinds of variants have also been commonly found in other monkey species, which have almost the same karyotype as the Japanese monkey and have not been reported to show frequent occurrence of limb malformation. We concluded therefore that chromosomal abnormalities could be excluded from the main causal factors for limb malformations of the Japanese monkey.

Density of Japanese Macaque (Macaca fuscata yakui) Males Ranging Alone: Seasonal and Regional Variation in Male Cohesiveness with the Group

Abstract. We conducted point censuses in Yakushima island to estimate the density of Japanese macaque (Macaca fuscata yakui) males ranging alone, focusing on its vegetational, seasonal, and regional variation. In highland areas, the detection frequency of males ranging alone did not differ among different types of vegetation, despite the latters effect on overall population density. The detection frequency of males ranging alone in the mating season was a third of that in the non-mating season. In the mating season, males exhibit strong cohesiveness with a group, probably in search of resident estrous females. Outside of the mating season, we detected 25% fewer males ranging alone in lowland areas, which have high population densities and strong inter-group competition, than in highland areas. The absolute density of males ranging alone was estimated to be 1.2–5.7 individuals/km2. Meanwhile, the group and population densities were 1.25/km2 and 19.3/km2, respectively. A considerable number of males therefore remained outside of groups, and male cohesiveness with groups is flexible in relation to ecological and social circumstances.