The Influence of Seasonal Variation on Chimpanzee (Pan troglodytes schweinfurthii) Fallback Food Consumption, Nest Group Size, and Habitat Use in Gishwati, a Montane Rain Forest Fragment in Rwanda

Abstract

The increased number of primates living in fragmented habitats necessitates greater knowledge of how they cope with large-scale changes to their environment. Chimpanzees (Pan troglodytes) are exceptionally vulnerable to forest fragmentation; however, little is known about chimpanzee feeding ecology in fragments. Although chimpanzees have been shown to prefer fruit when it is available and fall back on more abundant lower quality foods during periods of fruit scarcity, our understanding of how chimpanzees use fallback foods in forest fragments is poor. We examined how chimpanzees cope with periods of fruit scarcity in Gishwati Forest Reserve, a disturbed montane rain forest fragment in Rwanda. We assessed seasonal changes in chimpanzee diet and the use of preferred and fallback foods through fecal and food site analysis. We also examined seasonal variation in nest group size and habitat use through marked nest censuses. We found that chimpanzees experienced a seasonal reduction in preferred fruit availability, which led to a seasonal diet shift to more fibrous foods, including several that functioned as fallback foods. Our results suggest that during periods of fruit scarcity the chimpanzees also reduced nest group size. However, we found that the chimpanzees did not alter their habitat use between high-and low-fruit seasons, which suggests that the small size of the forest limits their ability to change their seasonal habitat use. Consequently, fallback foods appear to be particularly important in small food-impoverished habitats with limited ranging options.

Dietary variation and food hardness in sooty mangabeys (Cercocebus atys): Implications for fallback foods and dental adaptation

“…Demonstrating preference requires an independent assessment of availability and these authors operationalize their definition of preferred foods as ones that are "over-selected" or selected disproportionate to their availability. Preferred foods, conceived of in the context of some fallback models generally require little manual or masticatory processing and because they are normally rare in the environment, the limiting factor is finding them (e.g., Chancellor et al, 2012;Hanya and Bernard, 2012;Harrison and Marshall, 2011;Marshall and Wrangham, 2007). Preferred foods should be associated with adaptations for harvesting, i.e., detecting foods at a distance and for efficient locomotion between food patches.…”

“…The potential significance of fallback foods has been widely embraced by the anthropological community (e.g., Rosenberger, 2013) and is increasingly used to explain dietary variation and interpret masticatory morphology in a variety of extant and extinct primates (e.g., Alba et al, 2010;Chancellor et al, 2012;Daegling et al, 2013;Doran-Sheehy et al, 2009;Etiendem and Tagg, 2013;Grine et al, 2006aGrine et al, , 2006bGrueter et al, 2009;Hanya and Bernard, 2012;Irwin et al, 2014;Laden and Wrangham, 2005;Porter et al, 2009;Strait et al, 2009Strait et al, , 2013Ungar et al, 2008;Vogel et al, 2009;Wright et al, 2009). One feature linked to the fallback food concept is primate molar enamel thickness Lambert et al, 2004).…”

Genetic Sampling of Unhabituated Chimpanzees (Pan troglodytes schweinfurthii) in Gishwati Forest Reserve, an Isolated Forest Fragment in Western Rwanda

“…Recent surveys based on counting the nests that chimpanzees make afresh every evening suggested that this population consists of ca. 9-21 individuals (Barakabuye et al 2007;Chancellor et al 2012). Here we analyzed DNA from chimpanzee fecal samples collected below nests, along chimpanzee trails, and where chimpanzees had recently been seen or heard over a 9-mo period at Gishwati.…”

Tooth Wear Inclination in Great Ape Molars

“…Similarly, fruit is the preferred food of eastern chimpanzees. However, during periods of fruit scarcity, fallback foods, such as leaves, pith and bark, play an important part in their diet [Chancellor et al, 2012]. Thus, we could hypothesize that the lack of significant differences between the diet of western lowland gorillas and eastern chimpanzees could be related to the exploitation of similar foods, mainly consisting of fruit and herbaceous materials.…”

“…When chimpanzees face fruit scarcity, they tend to eat lower-quality foods (or fallback foods, which are more difficult to digest) consisting of leaves, seeds, blossoms, stems, bark and resin [e.g., Conklin-Brittain et al, 1998;Wrangham et al, 1998;Constantino et al, 2009;Wood and Schroer, 2012]. In particular, the diet of eastern chimpanzees ( Pan troglodytes schweinfurthii ), the sample analyzed in this study, is characterized by strong seasonal changes, with a shift to more fibrous foods, such as leaves, pith and bark, during periods of low fruit availability [Nishida et al, 1983;Wrangham et al, 1998;Emery-Thompson and Wrangham, 2008;Chancellor et al, 2012;Watts et al, 2012]. Comparatively, orangutans are also identified as primarily frugivorous but rely heavily on tough and highly fibrous fallback foods [Mackinnon, 1974[Mackinnon, , 1979Taylor, 1998Taylor, , 2002Taylor, , 2006Delgado and Van Schaik, 2000;Wich et al, 2009;Kanomori et al, 2010;Terhune, 2013].…”