Top > African Study Monographs > ASM Supplementary Issue Back Number > No.39 (2008)
Fruit Phenology and Ecology of Sympatric Gorillas and Chimpanzees in Tropical and Montane Forests.

Edited by Juichi YAMAGIWA


pp.1-2

Preface

Juichi YAMAGIWA

PDF file of body text (76 KB)


pp. 3-22

PHENOLOGY OF FRUITS CONSUMED BY A SYMPATRIC POPULATION OF GORILLAS AND CHIMPANZEES IN KAHUZIBIEGA NATIONAL PARK, DEMOCRATIC REPUBLIC OF CONGO

Juichi YAMAGIWA
Laboratory of Human Evolution Studies, Graduate School of Science, Kyoto University
Augustin Kanyunyi BASABOSE, Kiswele Prince KALEME
Centre de Recherche en Sciences Naturelles
Takakazu YUMOTO
Research Institute of Humanity and Nature

ABSTRACT
   Monthly fl uctuations in the abundance of fruits eaten by a sympatric population of gorillas (Gorilla beringei gaueri) and chimpanzees (Pan troglodytes schweinfurthii) were estimated by a transect system and a fruit trail system in the montane forest of Kahuzi-Biega National Park, Democratic Republic of Congo. Fruit species eaten by gorillas and chimpanzees and their preferences were defi ned mainly by fecal analysis. Data were collected for 80 months from 1994 to 2002, with a period of forced inactivity due to the civil war in 1997. A belt transect 5,000 m long and 20 m wide was set up in the study area to pass through most of the vegetation types in which gorillas and chimpanzees range, and 2,033 trees, including shrubs and strangling fi gs, above 10 cm in diameter at breast height (DBH) of 49 species from 29 families were identifi ed. Of these, fruits of 21 (6) species and 25 (12) species were eaten (preferred) by gorillas and chimpanzees, respectively. The fruit species preferred by gorillas were also preferred by chimpanzees. Monthly fruit index calculated from total basal area per ha and the proportion of the number of trees in fruit for each species shows a larger fl uctuation in the abundance of fruits eaten by chimpanzees than that by gorillas. Unlike the phenology of fruits in the lowland tropical forests, monthly fl uctuation in ripe fruit abundance negatively correlated with rainfall in some years. This tendency was more distinct for fruits preferred by gorillas in the primary forest. Fruit species preferred only by chimpanzees showed a distinct intra-specifi c synchrony in fruiting, while fruit species preferred by gorillas and chimpanzees did not. These differences in fruiting patterns may infl uence the foraging patterns of gorillas and chimpanzees. Gorillas tended to travel widely in a cohesive group and to increase their consumption of fruits in the primary forest during the dry season. By contrast, chimpanzees tended to continuously visit particular fruiting trees individually in a small home range throughout the entire year. Some tree species that have large basal areas and that bear fruits for a long period may be able to support the survival and sympatry of gorillas and chimpanzees.  

Key Words: Fruit phenology; Synchrony in fruiting; Montane forest; Gorilla; Chimpanzee; Foraging strategy.

PDF file of body text (754 KB)


pp. 23-39

FRUIT PHENOLOGY OF THE GREAT APE HABITAT IN THE MOUKALABA-DOUDOU NATIONAL PARK, GABON

Yuji TAKENOSHITA
Department of Children, Faculty of Children Studies, Chubu-Gakuin University
Chieko ANDO, Yuji IWATA, Juichi YAMAGIWA
Laboratory of Human Evolution Studies, Graduate School of Sciences, Kyoto University

ABSTRACT
   Fruit phenology of the Moukalaba-Doudou National Park (MDNP), Gabon is monitored as basic information on the fluctuation of food production for great ape populations. During the period from January 2003 to February 2007, we conducted a census on fallen fruits by the line transect method twice a month, in the process counting fallen fruit clusters and identifying fallen fruit species. We recorded 117 fallen fruit species during the study period. The majority of fruits came from trees. The number of fallen fruit clusters obtained in each census session correlated with the number of fallen fruit species found in the sessions. There was a marked seasonal pattern to fruit production, whereas the number of fallen fruit clusters as well as the number of species tended to be larger in the rainy season than in the dry season. Of the 31 major fallen fruit species, 15 species showed a fruiting peak in the rainy season, and five species peaked in the dry season, while 11 species showed no difference in fruiting abundance between the rainy and dry seasons. Candidates of keystone fruit species were identifi ed from species that fruit during the dry season. Five species of fruit, including the woody liana Cissus dinklagei, were constantly abundant, occurring in more than 70% of all census sessions. Four of them are important fruit food resources for the great apes. Several species including Klainedoxa gabonensis exhibited super-annual fl uctuation in their fruiting pattern. The existence of constantly abundant fruit species may have supported the high density of great apes in the MDNP.

Key Words: Fruit phenology; Chimpanzee; Gorilla; Diet; Moukalaba; Keystone fruit.

PDF file of body text (1,006 KB)


pp. 41-54

ESTIMATING GORILLA ABUNDANCE BY DUNG COUNT IN THE NORTHERN PART OF MOUKALABA-DOUDOU NATIONAL PARK, GABON

Yuji TAKENOSHITA
Department of Children, Faculty of Children Studies, Chubu-Gakuin University
 Juichi YAMAGIWA
Laboratory of Human Evolution Studies, Graduate School of Sciences, Kyoto University


ABSTRACT
    Nest count is not an appropriate method to estimate abundance of gorillas and chimpanzees where both species live sympatrically. To apply an alternative method that could estimate their abundance separately, we examined dung count for gorillas on line transects. In the northern part of Moukalaba-Doudou National park, Gabon, we conducted a survey of gorilla dung piles (DPs) along the 11 line transects of 44.3 km in total length. First, we counted and marked all encountered dung piles and estimated DP density by the distance sampling method. After two days, we walked the same transects and checked whether the marked DPs were still recognizable, in order to calculate a daily dung disappearance rate. Using DP density, daily dung disappearance rate and the defecation frequency extrapolated from the other western gorilla populations, we calculated the density of gorilla. DP density was estimated at 102.3 dps/ km2. Dung piles of gorillas are easily discriminated from those of chimpanzees, so dung pile density is considered as a good indicator of gorilla abundance. However, individual density derived from DP density, daily dung disappearance rate and defecation rate seemed to be signifi cantly overestimated. Precise information on dung decay duration, age/sex difference in defecation rate, dietary effects on defecation rate, and group-level DP production frequency are needed for a reliable individual density estimate. No signifi cant difference was found in the encounter frequency of dung piles between the home range of our habituated gorilla group and those of adjacent areas, suggesting an overall high density of gorillas in the northern part of the Park.

Key Words: Density estimate; Dung piles (DPs); Defecation rate; Gorilla; Moukalaba- Doudou; Conservation

PDF file of body text (680 KB)


pp. 55-69

PROGRESS OF HABITUATION OF WESTERN LOWLAND GORILLAS AND THEIR REACTION TO OBSERVERS IN MOUKALABA-DOUDOU NATIONAL PARK, GABON

Chieko ANDO, Yuji IWATA, Juichi YAMAGIWA
Laboratory of Human Evolution Studies, Graduate School of Sciences, Kyoto University


ABSTRACT
   We have conducted habituation of western lowland gorillas since May 2003 during a long-term socio-ecological survey on primates in Moukalaba-Doudou National Park (Moukalaba N.P.) in Gabon. After a training program to increase the skills of trackers to search for gorillas in tropical forest, we identifi ed one group named ‘Group Gentil’ (GG). Since October 2005, we have focused our efforts on habituating this group and carrying out all-day follows that have resulted in the identifi cation of most adult and subadult individuals in GG. Here, we describe the habituation process of GG and the major problems we faced in habituation. First, we had to employ inexperienced trackers and modify our methods according to the gorillas’ responses. Subsequently we continued to employ the same trackers and formed two teams consisting of researchers and trackers to search for gorillas on a daily basis. The skills of our trackers in performing constant and reliable follows of GG have gradually increased. Furthermore, our persistent follows seemed to have a less disruptive effect on their ranging patterns. Once all-day follows were achieved, GG came to tolerate our presence. Juveniles approached us with curiosity when the silverback male remained nearby. Males were habituated more quickly than females, as observed in other habitats. However, distinct differences were found in the responses to human observers between the silverbacks and females. Unlike mountain gorillas and eastern lowland gorillas, female western gorillas at Moukalaba showed aggressive responses to our approaches and occasionally attacked us with threatening vocalizations. Such female aggressiveness resembled that observed at Mondika in the process of habituation. However, while the silverback male usually ignored female aggression at Mondika, the silverback frequently rushed onto aggressive females to stop them at Moukalaba. Based on these similarities and differences in the habituation process at Moukalaba, we propose recommendations for achieving successful habituation.

Key Words: Western lowland gorilla; Habituation; Moukalaba-Doudou N.P.; Tracking skills; Female aggression.

PDF file of body text (322 KB)


PDF file of photographs (3,074 KB)