The Influence of Seasonal Frugivory on Nutrient and Energy Intake in Wild Western Gorillas

Abstract

The daily energy requirements of animals are determined by a combination of physical and physiological factors, but food availability may challenge the capacity to meet nutritional needs. Western gorillas (Gorilla gorilla) are an interesting model for investigating this topic because they are folivore-frugivores that adjust their diet and activities to seasonal variation in fruit availability. Observations of one habituated group of western gorillas in Bai-Hokou, Central African Republic (December 2004-December 2005) were used to examine seasonal variation in diet quality and nutritional intake. We tested if during the high fruit season the food consumed by western gorillas was higher in quality (higher in energy, sugar, fat but lower in fibre and antifeedants) than during the low fruit season. Food consumed during the high fruit season was higher in digestible energy, but not any other macronutrients. Second, we investigated whether the gorillas increased their daily intake of carbohydrates, metabolizable energy (KCal/g OM), or other nutrients during the high fruit season. Intake of dry matter, fibers, fat, protein and the majority of minerals and phenols decreased with increased frugivory and there was some indication of seasonal variation in intake of energy (KCal/g OM), tannins, protein/fiber ratio, and iron. Intake of non-structural carbohydrates and sugars was not influenced by fruit availability. Gorillas are probably able to extract large quantities of energy via fermentation since they rely on proteinaceous leaves during the low fruit season. Macronutrients and micronutrients, but not digestible energy, may be limited for them during times of low fruit availability because they are hind-gut fermenters. We discuss the advantages of seasonal frugivores having large dietary breath and flexibility, significant characteristics to consider in the conservation strategies of endangered species.

The distribution of plant consumption traits across habitat types and the patterns of fruit availability suggest a mechanism of coexistence of two sympatric frugivorous mammals

“…Although fallback foods have been viewed as those of low nutritional value (Doran‐Sheehy et al, ; Rogers et al, ), determination of fallback foods has rarely been carried out at the species level (Basabose & Yamagiwa, ). However, the protein content of fruits may be an important source of energy for great apes (Felton et al, ), and the nutritional content of fruiting species may differ (Masi et al, ). Our results support the classification by many other studies of Ficus spp.…”

What, where and when: spatial foraging decisions in primates

“…For example, folivorous primates' resources are more homogeneously distributed and are present throughout the year (and are therefore easily accessible) than are resources of fruit specialists (e.g. Chapman, White & Wrangham, 1994;Chapman, Wrangham & Chapman, 1995;Sayers, 2013;Masi et al, 2015;Masi & Breuer, 2018).…”

Variation in the social organization of gorillas: Life history and socioecological perspectives

“…Mountain gorillas live in habitats with higher densities of terrestrial herbaceous vegetation and lower fruit availability than western gorilla habitat (Table ) . The diet of western gorillas includes significant quantities of fruit, which tends to be more spatially and temporally clumped than herbaceous vegetation (Table ) . Western gorillas have longer daily travel distances and are less spatially cohesive (i.e., larger average interindividual distance) than mountain gorillas, suggesting that their food resources are less abundant and more clumped .…”

“…[31][32][33][34] The diet of western gorillas includes significant quantities of fruit, which tends to be more spatially and temporally clumped than herbaceous vegetation (Table 2). 30,32,35,95 Western gorillas have longer daily travel distances and are less spatially cohesive (i.e., larger average interindividual distance) than mountain gorillas, suggesting that their food resources are less abundant and more clumped. [96][97][98] Therefore, both scramble competition and contest competition are predicted to be higher within groups of western gorillas than mountain gorillas, which could lead to more constraints on their group size.…”

“…167,168 By the late 1990s, one group of western gorillas was habituated at Bai Hokou, which eventually led to additional studies on their feeding ecology and aspects of their social behavior. 95,96,169 Additionally, in the mid-1990s, Diane Doran began the Mondika study site, about 50 km away from Bai Hokou, where research on two groups of habituated gorillas provided more information on their social behavior. 30,98,104,170,171 Groups have also been habituated in Odzala National Park, Republic of Congo.…”