Hiroyuki Takasaki

Troop size, habitat quality, and home range area in Japanese macaques

SummaryThe correlation between troop size (N) and home range area (R) is examined in terms of habitat quality with 32 data sets for the Japanese macaque (Macaca fuscata) from its entire distribution range. The habitat quality is represented by the vegetation type and the degree the habitat is disturbed. A proportional relationship is found between N and R when the two major vegetation types (deciduous and evergreen) are discriminated and only the data from relatively undisturbed habitats are considered. This result is discussed in relation to bioenergetics.

New records of within-group infanticide and cannibalism in wild chimpanzees

Two cases of within-group infanticide and cannibalism were observed among the M Group chimpanzees of the Mahale Mountains, Tanzania. In both cases, victimized infants were male, 5 – 6 months of age, and in good health when killed. Four to five years have passed since the mothers of the victims immigrated into M Group as nulliparous immigrants. In one case the 2nd-ranking male was observed to detach the infant from the mothers belly. Both infants were finally killed by the alpha male after several adult males scrambled for the bodies. There was no evidence that the mothers had mated with males other than those of M Group. Nor was there evidence that the mothers had restrictive mating relationships with some of the M Group adult males. What little evidence is available shows that the mothers had mated mostly with adolescent and other immature males during their conception cycles. However, at least in one case, the mother began to mate more with adult males rather than with immature males after the infanticide. It is proposed that the function of within-group male infanticide can be explained by the male-male competition hypothesis developed for hanuman langurs and other nonhuman primates.

Measurement of the energy release rate and the reconnection rate in solar flares

By using the method presented by Isobe et al., the nondimensional reconnection rate vin/vA has been determined for the impulsive phase of three two-ribbon flares, where vin is the velocity of the reconnection inflow and vA is the Alfven velocity. The nondimensional reconnection rate is important to make a constraint on the theoretical models of magnetic reconnection. In order to reduce the uncertainty of the reconnection rate, it is important to determine the energy release rate of the flares from observational data as accurately as possible. To this end, we have carried out one-dimensional hydrodynamic simulations of a flare loop and synthesized the count rate detected by the Soft X-Ray Telescope (SXT) aboard the Yohkoh satellite. We found that the time derivative of the thermal energy contents in a flare arcade derived from SXT data is smaller than the real energy release rate by a factor of 0.3-0.8, depending on the loop length and the energy release rate. The results of the simulations are presented in the paper and used to calculate the reconnection rate. We found that the reconnection rate is 0.047 for the X2.3 flare on 2000 November 24, 0.015 for the M3.7 flare on 2000 July 14, and 0.071 for the C8.9 flare on 2000 November 16. These values are similar to that derived from the direct observation of the reconnection inflow by Yokoyama et al. and consistent with the fast reconnection models such as that of Petschek.

Multiple plasmoid ejections and associated hard x-ray bursts in the 2000 November 24 flare

The Soft X-ray Telescope (SXT) on board Yohkoh revealed that the ejection of X-ray emitting plasmoid is sometimes observed in a solar flare. It was found that the ejected plasmoid is strongly accelerated during a peak in the hard X-ray (HXR) emission of the flare. In this paper, we present an examination of the GOES X 2.3 class flare that occurred at 14:51 UT on 2000 November 24. In the SXT images, we found multiple plasmoid ejections with velocities in the range of 250-1500 km s–1, which showed blob-like or loop-like structures. Furthermore, we also found that each plasmoid ejection is associated with an impulsive burst of HXR emission. Although some correlation between plasmoid ejection and HXR emission has been discussed previously, our observation shows similar behavior for multiple plasmoid ejection such that each plasmoid ejection occurs during the strong energy release of the solar flare. As a result of temperature-emission measure analysis of such plasmoids, it was revealed that the apparent velocities and kinetic energies of the plasmoid ejections show a correlation with the peak intensities in the HXR emissions.

Aggression toward Large Carnivores by Wild Chimpanzees of Mahale Mountains National Park, Tanzania

In the Mahale Mountains National Park of Tanzania, a group of about 33 chimpanzees were observed to surround a leopard den containing a mother and at least one cub and to drag out and kill the cub. This is the first report of chimpanzees or any other primate species killing their potential predators offspring. The incident suggests that chimpanzees, without any weapons, can manage to defend themselves against a carnivore of at least up to leopard size, and implicates how the early hominids may have reacted against their potential predators.

Winter Range Utilization of a Japanese Macaque Troop in a Snowy Habitat

The winter range utilization pattern of a Japanese macaque troop in a snowy habitat was studied. The vegetation areas essential for subsistence were found to be relatively undisturbed mixed and deciduous forests. The concept of essential resource area (ERA) is defined. Our comparison among three troops in the same habitat in the past and present with different population densities indicated that the per capita ERA is quite important in determining the range area. This implies that the population and range area are resource-correlated.

Female life history and mating patterns among the M group chimpanzees of the Mahale national park, Tanzania

The mating behavior of receptive females in the M group chimpanzees (Pan troglodytes schweinfurthii) of the Mahale Mountains, western Tanzania, was studied by intensive sampling over a period of 5 months. Restrictive matings were observed only between parous females mostly in the ovulatory stage and prime adult males, in particular the alpha. Young, nulliparous and/or non-ovulatory females tended to mate with immature or low-ranking adult males. By contrast, older, parous and/or ovulatory females tended to mate with adult and higher-ranking males. These confirmed the results of a previous extensive study of the same group. In addition, gradual shift from opportunistic to restrictive matings after inter-unit-group transfer was revealed for 2 ex-K-group parous females. The findings were discussed in relation to the life history of female chimpanzees.

Physiological activities and the active constituents of potentially medicinal plants used by wild chimpanzees of the Mahale mountains, Tanzania

Potential medicinal plants for wild chimpanzees have been studied in order to discover their physiologically active compounds. Tests of the physiological activity of 3 plant species—Vernonia amygdalina, Aspilia mossambicensis, andFicus exasperata—indicate that they contain a variety of active compounds. From one species,V. amygdalina, an antitumor agent and 2 possible antitumor promoters are identified. Furthermore, steroid glucosides were isolated as the bitter substances. These structurally new compounds are expected to exhibit a number of significant physiological activities. The chemical investigation of possible medicinal plants used by chimpanzees should be helpful in recovering naturally occurring compounds of medicinal significance for human use.

New Evidence on Scavenging Behavior in Wild Chimpanzees

the period between 0.8 and 3 years of age and the early pubertal phase); and (3) a shift of developmental stages towards earlier calendar years due to acceleration of development. Examination of figures 1and 2 suggests the simultaneous operation of all three. Their interrelations have not so far been elucidated and require further study. It is of interest that whereas for the population of Warsaw in the past decade or so the rate of increase in stature has been greater in boys (on the average, 1.3%) than in girls (1.2%), for the populations of the Silesian towns and of the rural regions it has been greater in girls than in boys (except in the youngest and oldest age-groups). Sexual dimorphism in stature shows great changes during the period investigated, although materials for an analysis of this phenomenon are scarce. Between 1879 and 1959, a substantial change took place in the preschool years; in 1879 dimorphism was most intense at early preschool age, decreased with the approach of the prepubertal period, and rose again with the beginning of the pubertal phase (fig. 3). The studies performed in 1959 and 1979 show great similarities in stature dimorphism. Dimorphism is somewhat more intense at 3-4 years of age and decreases until the 12th year, whereupon it rapidly rises. It is assumed that changes in dimorphism are related primarily to differences in the living conditions of the sexes, which are known to have changed greatly during the past century.

Newly acquired feeding habits among the chimpanzees of the Mahale Mountains National Park, Tanzania

The M group chimpanzees (Pan troglodytes schweinfurthii) of the Mahale Mountains National Park, Tanzania, began to feed on three agricultural fruit species, guava, mango and lemon. It took them 7–8 years until they began to taste these fruits since the villagers left the park area in 1974. Although adult chimpanzees are conservative in their feeding habits, they are capable of rapidly acquiring new feeding habits, or new traditions, once they notice that the food is suitable.