抄録
Ecological study of wild chimpanzees (Pan troglodytes schweinfurthii) has been conducted in Ugalla area, western Tanzania. Ugalla is one of the driest habitats of chimpanzees. Also, Ugalla River is the eastern boundary of chimpanzee distribution. This area covers 2, 800km2 with elevation from 1, 100m to 1, 600m. The majority of Ugalla area is deciduous woodland dominated by Brachystegia sp. and Julbernardia sp. (‘Miombo’ in local name). Woodland dominated by B. bussei is formed in mountainous areas. Two types of evergreen forests were also formed in mountainous areas. One is a small patchy forest dominated by Monopetalanthus richadsiae (Kabamba-jike) on a hill or beside a cliff, and the other is a kind of riverine forest dominated by Julbernardia unijugata (Kabamba-dume) along a steep valley. During the dry season, chimpanzees frequently used these forests as sleeping sites, and B. bussei woodland as feeding sites. Nest census showed that the population density of chimpanzees in Ugalla was 0.05 individual/km2, although the density of mountainous areas was higher than that of flat areas. Four or five communities (unit groups) each of which has approximately 30 individuals may inhabit the Ugalla. The both estimations indicate that the total number of 120-150 chimpanzees inhabit this area. If several communities divide the whole Ugalla area, each community should have a huge home range. For a certain period, however, chimpanzees might be ranging in a small part of their annual home range, and seasonally shift such areas. In the daytime, chimpanzees formed a small feeding party to exploit poor and sparse food resources. On the other hand, they formed a larger sleeping party at night, because of high predation pressure of large carnivores. Understanding such chimpanzee adaptation to dry and open habitat in the savanna woodland can shed light onto behavioral ecology of early hominid. Besides seven species of primates including chimpanzees inhabit the Ugalla area. Other large and middle-sized mammals and rodents in Ugalla are also listed in tables of this report.
