Chimpanzees (Pan troglodytes) in savanna landscapes

Abstract

Chimpanzees (Pan troglodytes) are the only great apes that inhabit hot, dry, and open savannas. We review the environmental pressures of savannas on chimpanzees, such as food and water scarcity, and the evidence for chimpanzees' behavioral responses to these landscapes. In our analysis, savannas were generally associated with low chimpanzee population densities and large home ranges. In addition, thermoregulatory behaviors that likely reduce hyperthermia risk, such as cave use, were frequently observed in the hottest and driest savanna landscapes. We hypothesize that such responses are evidence of a “savanna landscape effect” in chimpanzees and offer pathways for future research to understand its evolutionary processes and mechanisms. We conclude by discussing the significance of research on savanna chimpanzees to modeling the evolution of early hominin traits and informing conservation programs for these endangered apes.

Wild chimpanzee behavior suggests that a savanna-mosaic habitat did not support the emergence of hominin terrestrial bipedalism

“…Issa Valley in western Tanzania is characterized as a savanna-mosaic ( 14 , 35 , 39 ) similar to the paleoenvironments reconstructed for the early hominins Orrorin , Ardipithecus ramidus , and Australopithecus afarensis ( 9 – 13 ) and hosts a recently habituated (2018) chimpanzee community ( P. t. schweinfurthii ). The area is a mosaic of miombo woodland with strips of evergreen riparian forest (classed as open and closed vegetation, respectively; Fig.…”

“…Instead, the earliest (putative) fossil hominins, including Orrorin (6 Ma) ( 9 ), Ardipithecus (5.8 to 4.4 Ma) ( 10 , 11 ), and early Australopithecus (4.2 to 2.9 Ma) ( 12 , 13 ), would have moved and foraged in mosaic savanna habitats dominated by woodland with strips of riparian forest vegetation, often termed “savanna-woodland” or “savanna-mosaic” (used hereafter). Compared to tropical forest, these savanna-mosaic habitats would have elicited different selective pressures associated with reduced tree density and increased seasonality ( 14 , 15 ). For example, savanna-mosaics have temporally and spatially sporadic food sources, as well as greater predatory pressure, which are hypothesized to have selected for bipedalism as an efficient mode of terrestrial travel ( 6 , 16 , 17 ).…”

“…In the absence of direct fossil evidence, and due to difficulties in reconstructing the relationship between behavior and habitat from morphology alone, quantitative studies of locomotor ecology of wild, extant primates have been key to providing valuable insights into how and why bipedalism may have evolved [e.g., ( 5 , 28 – 30 )]. Notably, extant apes living in savanna-mosaic habitats analogous to those of early hominins provide ideal models to test the “savanna effect” on ape and, by extension, hominin behavior ( 14 , 31 ). As our closest living relatives, chimpanzees ( Pan troglodytes ) and bonobos ( Pan paniscus ) are informative analogs ( 32 ), regardless of whether our last common ancestor was Pan -like ( 33 , 34 ).…”

Wild Chimpanzee Welfare: A Focus on Nutrition, Foraging and Health to Inform Great Ape Welfare in the Wild and in Captivity

“…The breadth of a chimpanzee diet varies between populations, habitat types (forest versus savanna) as well as the level of exposure to anthropogenic factors [ 7 ]. For instance, wild chimpanzees living in savanna landscapes have diets typically low in species richness [ 14 ] in comparison to forested populations. Some populations excel at making and using tools to acquire high energy food sources like honey, nuts, and insects [ 9 , 13 , 14 , 15 , 16 , 17 ].…”

“…For instance, wild chimpanzees living in savanna landscapes have diets typically low in species richness [ 14 ] in comparison to forested populations. Some populations excel at making and using tools to acquire high energy food sources like honey, nuts, and insects [ 9 , 13 , 14 , 15 , 16 , 17 ]. Other populations spend considerable amounts of time hunting other primates or small mammals [ 18 , 19 , 20 ].…”