title: Chimpanzee (Pan troglodytes schweinfurthii) behavioral responses to resource scarcity in the savanna-woodland environment of Issa valley, Tanzania — Study of feeding, ranging, and grouping patterns
Creators: name: Giuliano, C
Publisher: name: Liverpool John Moores University
Year: 2022

description: To survive and reproduce, primates must consume sufficient amounts of resource. Because they live in seasonal environments and mostly rely on vegetative foods, primates face temporal variations in food abundance and quality, and food shortages often have negative repercussions on their energy balance, fecundity, growth, and survival. To limit these impacts and maintain sufficient nutrient and energy intake during lean periods, primates exhibit a large range of adaptations including adjusting their diet, ranging behavior and/or group size. Chimpanzees (Pan troglodytes) are one of the most studied animals but despite nearly six decades of field research, gaps remain in our knowledge of the species, particularly when it comes to communities inhabiting savanna-woodlands, the ecological edge of the species range. Savanna-woodlands differ from forests in having substantially less rainfall, which is strongly seasonal, as well as lower plant density and diversity, all of which result in resource scarcity and important fluctuations in its availability. The selective pressures operating on chimpanzees in these landscapes are thus predicted to be different than those in forests, potentially eliciting adaptations distinct from adaptations to a forested habitat, especially during times of resource (both food and water) scarcity. However, to date, we have only limited behavioral data from habituated communities in savanna-woodlands, thus restricting our ability to explore these ideas. I investigated chimpanzee (P. t. schweinfurthii), diet, ranging and grouping patterns in the savanna-woodland environment of Issa valley, Tanzania, and particularly their correlations to seasonal fluctuations in resource availability. I also compared the diet, ranging and grouping patterns observed at Issa with those of other communities. I found that, when preferred foods were scarce, Issa chimpanzees consumed young leaves from tree species growing in the open woodland habitat. In contrast to previous reports from other chimpanzee communities, during periods of low food availability Issa chimpanzees significantly increased their daily path length. Water scarcity, however, did not influence their daily path length, and neither seasonal fluctuation in food nor water availability influenced habitat use. I found that party size at Issa was significantly influenced by seasonal variations in food but not water availability and was higher in open habitat, which is potentially characterized by a high predation risk. In general, Issa chimpanzees consumed less plant species than chimpanzees at more forested sites. Like elsewhere, they consumed mostly fruit, but other items such as leaves, flowers, and termites were also important in their annual diet probably because they provide essential proteins. Issa yearly home range was larger than most other communities for which data are available. Finally, compared to other communities, the Issa community was highly cohesive, possibly due to a combination of its small size and the potential threats (predators, neighboring communities) in their home range. By providing data from direct observations of a chimpanzee population living in an under‐studied biome, the present study brings new insights into chimpanzee behavioral responses to seasonal fluctuations in ressource availability, into the relationships between environment and behavior for this species, and into chimpanzee behavioral diversity in general. Furthermore, chimpanzee behavioral studies may be of great value to the paleoanthropological scientific community. The results of the current study could be useful to interpret archaeological records and infer extinct hominin behavior, as well as to highlight what adaptations may have set the principles for the differentiation between human and chimpanzee lineage.