ギニア共和国・ボッソウにおけるチンパンジー研究小史

抄録

This review summarizes the findings from 40 years of research on a chimpanzee group at Bossou, Guinea, conducted mainly by two research teams, one from the University of Amsterdam, Netherlands, and the other from Kyoto University, Japan, and reports the current conservation status of the chimpanzee group.
Research in the 1960's by the Dutch team consisted of short-term, ‘testing-a-hypothesis’ type projects, which focused on the chimpanzees' agonistic behavior towards predators. They used a unique field-experiment method, with an artificial leopard, to see how the chimpanzees responded to the stimulus. The experiments revealed a variety of agonistic reactions by chimpanzees, including tool-using behavior such as throwing a branch and using a stick as a club.
In 1976, the Japanese team launched a long-term project, based on recognizing each chimpanzee individually. Although diverse topics have been covered to date, a focus has been tool use. Starting with the first substantial direct observation of nut cracking by wild chimpanzees, many other types of tool use have since been described, including ant dipping, pestle pounding, and algae scooping. A series of field experiments followed that revealed many details about nut cracking by chimpanzees: hand preference, metatool, developmental process, etc. Feeding ecology is a more recent topic, and the utilization of oil palm as a ‘keystone resource' when fruit is scarce, using two types of tool, proved to have significant ecological importance. Unique social characteristics like male immigration, close between-female relationships, and females’ high reproductive performances have been brought to light and require more ecological and genetic study to understand their uniqueness comprehensively.
As for the conservation status of Bossou chimpanzees, the population size has fluctuated, but has been essentially stable during the study period. The reproductive parameters appear good, but juveniles of both sexes tend to disappear for unknown reasons. The people of Bossou have a strong religious motivation for conserving small patches of forest and the chimpanzees living there, and there is good collaboration among the Bossou people, government institutions and researchers when dealing with conservation problems. Current concerns seem to be the genetic isolation from a neighboring chimpanzee population on Mt. Nimba, and crop damage caused by the chimpanzees.