The diet of open-habitat chimpanzees (Pan troglodytes schweinfurthii) in the Issa valley, western Tanzania

Abstract

Comparative data on the diets of extant primates inform hypotheses about hominin resource use. Historically, data describing chimpanzee diets stem primarily from forest-dwelling communities, and we lack comparative data from chimpanzees that live in mosaic habitats that more closely resemble those reconstructed for Plio-Pleistocene hominins. We present data on the diet of a partially-habituated community of open habitat chimpanzees (Pan troglodytes schweinfurthii) from the Issa valley, western Tanzania, collected over a four-year period. Based mostly on macroscopic faecal analysis, Issa chimpanzees consumed a minimum of 69 plant species. There was no relationship between plant consumption and either fruit availability or feeding tree density; the most frequently consumed plant species were found in riverine forests, with woodland species consumed more frequently during the late dry season. We conclude by contextualising these findings with those of other open-habitat chimpanzee sites, and also by discussing how our results contribute towards reconstructions of early hominin exploitation of mosaic landscapes.

Food mechanical properties and isotopic signatures in forest versus savannah dwelling eastern chimpanzees

“…These species feeding times agreed well with long-term observations of the dry season at this site 8 . At Issa, 19 species were tested, including samples from Ficus , Saba , and Garcinia (Table 3) that are considered year-round staple foods 10 . In the dry season at Issa, chimpanzees are thought to rely more on the woodland plant genera, and our sample reflected this with the inclusion of eight mainly woodland species.…”

“…In chimpanzees ( Pan troglodytes ), direct behavioural observation and indirect methods such as isotopic and faecal analysis have allowed a rather in-depth knowledge of what their diets are composed of 2–10 , and thus allow for some comparison with the putative diets of the earliest hominins 11 . However, in such studies, foods are still largely categorised in very broad terms (e.g., fruits, leaves, bark) that do not faithfully track their mechanical properties 12 .…”

Seasonal Variation in Physiology Challenges the Notion of Chimpanzees (Pan troglodytes verus) as a Forest-Adapted Species

“…As such, our interpretation of the breadth of chimpanzee ecological and environmental tolerance shapes our perception FIGURE 1 | Average annual temperature ( • C) and annual rainfall (mm) for chimpanzee long-term research sites (n = 10) (Data are derived from Head et al, 2011;Matsuzawa et al, 2011, this study;Lindshield, 2014;Piel et al, 2017).…”

“…Floral diversity is likewise consistently lower in savanna habitats, which has itself been proposed to be limiting to the chimpanzee biogeographical range (Kortlandt, 1983). This reduced floral diversity in savanna habitats is reflected in lower chimpanzee dietary breadth (Suzuki, 1969;McGrew et al, 1988;Pruetz, 2006;Lindshield et al, 2017;Piel et al, 2017), and has been argued as an indicator that savanna chimpanzees face resource scarcity (Pruetz, 2006;Bertolani and Pruetz, 2011;Lindshield, 2014).…”

“…This dehydration pressure likely originates from the coupling of high temperatures and the timing of particularly water-scarce periods, when little to no standing water is available, and chimpanzees must choose between meeting other basic requirements (i.e., feeding, socializing) and hydration maintenance. Lastly, savannas are also expected to be considerably more seasonal than more moderate habitats (Alberts et al, 2005;Piel et al, 2017). In order to counter the challenges of heat, water, and nutritional or energetic stresses faced by chimpanzees at the margins of their ecological niche, flexible dietary or behavioral strategies to meet shifting requirements may be needed if and when these challenges are encountered simultaneously.…”