Initial studies on the contributions of body size and gastrointestinal passage rates to dietary flexibility among gorillas.
Large body size has been traditionally seen as the primary dietary adaptation of gorillas, facilitating their consumption of fibrous foods (Schaller ¿1963 The Mountain Gorilla; Watts ¿1990 Int. J. Primatol. 11:21-45). Nevertheless, recent research has emphasized frugivory among western lowland gorillas, as well as the influence of habitat and seasonality on gorilla diet and behavior across subspecies (Watts ¿1990 Int. J. Primatol. 11:21-45; Tutin et al. ¿1991 Philos. R. Soc. Trans. Lond. Biol. 334:179-186; Remis ¿1994 Ph.D. Thesis, ¿1997a Am. J. Primatol. 43:87-109, ¿1997b Am. J. Primatol. 43:111-133, ¿1998 Primate Locomotion: Recent Advances, p 95-(1)108, ¿1999 Primates 40:383-396; Nishihara ¿1995 Primates 36:151-168; Goldsmith ¿1999a Int. J. Primatol. 20:1-23, Goldsmith [1999b] Nonhuman Primates, p 58-63). This study provides preliminary data to address the physiological underpinnings of dietary flexibility among gorillas, and their consumption of a broad range of fibrous and tannin-rich foods. To date, little is known about the digestive physiology of the African apes (but see Milton ¿1984 Adaptations for Foraging in Nonhuman Primates, p 249-279, Milton  ¿1999Evol. Anthropol. 8:11-20; Milton and Demment ¿1988 J. Nutr. 118:1082-1088; Lambert ¿1997 Ph.D. Dissertation), although gastrointestinal morphology and proportions are roughly similar among species ( Chivers and Hladik ¿1980 J. Morphol. 166:337-386). This study provides additional experimental data on the gastrointestinal passage times of gorillas (Gorilla gorilla gorilla) fed a captive diet in a zoological park setting and discusses results in relation to field research on gorilla feeding ecology. In this study, 480 small plastic markers were fed to six captive gorillas. The mean gut retention time (MRT) of the adult gorillas in this study was 50 hr, longer than the 31 hr reported for chimpanzees fed a similar diet (Lambert ¿1997 Ph.D. Dissertation). These data suggest that gorillas may retain foods in their gastrointestinal tracts longer than smaller hominoids, and that the large body size likely forms the primary basis for consumption of fiber. This research provides additional data to contribute to our understanding of the relationships of body size and morphology to ecology, and the evolution of body size, foraging strategy and social organization among the African apes.