Dietary variability of western gorillas (Gorilla gorilla gorilla)

Abstract

Spatial and temporal variability in the availability of food resources will lead to variation in a species' diet, which can then influence patterns of space use, sociality, and life history characteristics. Despite such potential impacts, little information is available about dietary variability for some species with large geographical ranges. Here we quantify the diet and nutritional content of plants consumed by western lowland gorillas (Gorilla gorilla gorilla) in Loango National Park, Gabon over a 2.6 year period and make comparisons with two study sites located 800 km away. The major foods consumed by the Loango gorillas differed greatly from the other two study sites, but gorillas at all three locations spent a similar proportion of feeding time consuming herbaceous vegetation and tree leaves (~ 50%) and fruit (35%). The Loango gorillas spent approximately 10% of feeding time eating nuts, which were not consumed at the other two study sites. Gorillas at those sites spent about 5% of feeding time eating insects, which were not consumed by Loango gorillas. Even though the species composition of the diet differed among the three sites, the nutritional composition of the major food items differed very little, suggesting that western gorillas consume foods of similar nutritional values to meet their dietary needs. This study shows the flexibility of diet of a species with a wide geographic distribution, which has implications for understanding variation in life history characteristics and can be useful for conservation management plans.

Fig 1. Seasonal changes of the monthly fruit availability (red line) and the monthly level of frugivory (blue line) of one group of western lowland gorillas in Loango National Park from 2018–2020.

See Methods for how the fruit availability index was calculated (composite of density of trees, mean basal area of each tree species, and percentage of trees in phenology study with ripe fruit in each month). Level of frugivory is the percent of feeding time spent consuming fruit (see Methods for further explanation).