Group differences in feeding and diet composition of wild western gorillas

Abstract

The ecological-constraints model posits that living in larger groups is associated to higher travel costs and reduced nutritional intake due to within-group feeding competition setting upper group size limits. While this is critical for frugivorous mammals, the model is less ubiquitous for folivores who feed on more abundant and evenly distributed food. The seasonally frugivorous diet of western gorillas (Gorilla gorilla) provides the opportunity to study the ecological-constraints model in the largest primate species. We investigated how two groups of western gorillas of differing sizes (N = 9, N = 15) in Central African Republic, responded to seasonal variation in fruit availability in terms of activity and diet. We used continuous focal animal sampling during periods of high (July–August 2011) and low (October 2011–January 2012) fruit availability, measured by monthly phenological scores. While diet diversity, resting and moving time did not differ between groups, overall the smaller group spent more time feeding than the larger group although this became less evident when fruit was more available. The smaller group was more frugivorous than the larger group. However, the larger group increased more steeply fruit consumption when fruit was more available, and incorporated more insects, young leaves and bark when fruit was less available, when compared to the smaller group. Up to a certain limit, the flexibility of large, seasonal frugivores to survive on a more folivorous diet may buffer the upper limit group size, suggesting deviation from the ecological-constraints model as in some folivores.

Passive segregation and multi-scale space-use adjustments to socio-ecological variables in western gorillas

“…of their home range, while smaller groups had less than 20% (Caillaud et al 2014). However, for larger differences in group size we cannot exclude asymmetric space use may exist also in western gorillas, as group size affects diet choice in this species (Fuh et al 2022).…”

Plant diversity in the diet of Costa Rican primates in contrasting habitats: a meta-analysis

“…Among vertebrates, non-human primates (NHP) are one of the most eclectic or flexible groups with respect to diet [2,[10][11][12], a crucial behavior for their medium and longterm survival in human-modified and/or strongly seasonal habitats (2,(12)(13)(14). While some NHP species are highly specialized (e.g.…”

Feeling a bit peckish: Seasonal and opportunistic insectivory for wild gorillas

“…Great ape insectivory also tends to be seasonal (e.g., Pan troglodytes : Bogart & Pruetz, 2011; Goodall, 1968; e.g., Gorilla spp. : Cipolletta et al, 2007; Deblauwe, 2009; Fuh et al, 2022; Masi et al, 2015; Tutin & Fernandez, 1992), although it is not entirely clear why. While correlations between insect consumption and either fruit consumption, insect availability or rainfall have been tested (Bogart & Pruetz, 2011; Cipolletta et al, 2007; Deblauwe, 2009; Doran et al, 2002; Fox et al, 2004; Goldsmith, 1999; Tutin & Fernandez, 1992) the results have been difficult to interpret given the complex interaction of ecological and nutritional factors affecting its variation (Cipolletta et al, 2007; Deblauwe, 2009; Tutin & Fernandez, 1992).…”

“…However, the majority of these previous studies were based on indirect observations that likely underestimate the quantity of insects consumed (Cipolletta et al, 2007; Deblauwe, 2009; Deblauwe et al, 2003; Goldsmith, 1999; Rogers et al, 1988; Tutin & Fernandez, 1992). In addition, none of the studies that were based on direct observations of western gorilla feeding behavior (Doran‐Sheehy et al, 2009; Fuh et al, 2022; Lodwick & Salmi, 2019; Masi et al, 2015) have investigated ecological variables that might trigger seasonal insectivory.…”

“…Since termites are limited and monopolizable food resources, if insect feeding is an opportunistic behavior in western gorillas (as suggested by Salmi et al, 2020), silverbacks should feed more on termites than other group members when the opportunity arises (i.e., when finding a termite mound on the path or in termite‐rich vegetation), given their priority access over food (Masi et al, 2009; Remis, 1994). On the contrary, being the lowest ranking individuals with regards to food access (Fuh et al, 2022; Yamagiwa, 1992), subadults are expected to feed less on insects compared to other individuals. In terms of nutrition, if gorillas adjust insect feeding according to nutritional needs, we predict that juveniles and adult females will feed more on insects because of the greater nutritional needs for proteins, fats and other nutrients for growth and reproduction, respectively (Altmann, 2001; Masi et al, 2009; Nowell & Fletcher, 2007).…”