Applying wet sieving fecal particle size measurement to frugivores: A case study of the eastern chimpanzee (Pan troglodytes schweinfurthii)

Abstract

Objectives Fecal particle size (FPS) as quantified by wet sieving analysis is a measure of chewing efficiency relevant for the understanding of physiological adaptations and constraints in herbivores. FPS has not been investigated systematically in frugivores, and important methodological problems remain. In particular, food items that are not chewed may skew estimates of FPS. We address such methodological issues and also assess the influence of diet type and age on FPS in wild chimpanzees. Materials and Methods 130 fecal samples of 38 individual chimpanzees (aged from 1.3 to ~55 years) from the Kanyawara community of Kibale National Park (Uganda) were collected during three fruit seasons and analysed using standardized wet sieves (pores from 16 mm to 0.025 mm). The effects of using different sieve series and excluding large seeds were investigated. We also assessed the relationship between FPS and sex, age and fruit season. Results The treatment of seeds during the sieving process had a large influence on the results. FPS was not influenced by chimpanzee sex or age, but was smaller during a fig season (0.88 ±0.31 mm) than during two drupe-fruit seasons (1.68 ±0.37 mm) (0.025–4 mm sieves, excluding seeds). Discussion The absence of an age effect on FPS suggests that dental senescence might be less critical in chimpanzees, or in frugivores in general, than in folivorous herbivores. To increase the value of FPS studies for understanding frugivore and hominoid dietary evolution we propose modifications to prior herbivore protocols.

Faecal Particle Size in Free-Ranging Proboscis Monkeys, Nasalis larvatus: Variation between Seasons

“…When large seeds (≥2 mm) were retained intact in sieves, they were removed, weighed and subtracted from the respective sieve weight. However, the smaller (< 2 mm) and numerous seeds, such as Ficus and Nauclea seeds, were logistically impossible to remove from the analysis [Weary et al, 2017].…”

“…Measuring faecal particle size by wet sieving analysis is an established non-invasive approach to determine the chewing efficiency of mammals [Fritz et al, 2009]. Several studies have focused on faecal particle size in mammals [Fritz et al, 2009;Clauss et al, 2015], or more specifically in ruminants [Renecker and Hudson, 1990;Clauss et al, 2002] and primates [Dunbar and Bose, 1991;Matsuda et al, 2014;Venkataraman et al, 2014;Weary et al, 2017]. Across mammals, the size of faecal particles usually increases with animal body mass [Fritz et al, 2009].…”

“…For instance, in gelada baboons (Theropithecus gelada), chewing efficiency decreases during the dry season when individuals feed on tougher non-preferred food items, with a more distinct effect in older individuals [Venkataraman et al, 2014]. The opposite is observed in frugivorous chimpanzees (Pan troglodytes schweinfurthii): MPS is higher when chimpanzees feed on drupe fruits (preferred foods) than on figs (non-preferred foods) [Weary et al, 2017]. The authors suggested that chewing efficiency might be less critical in frugivores than in typical folivores, because they did not observe an effect of age on MPS.…”

“…Extending the sieve column (adding larger top or smaller bottom sieves) is known to influence MPS measurements [Fritz et al, 2012], as well as including the weight of unchewed items (i.e., large seeds) and maximum particle length in the MPS calculation [Weary et al, 2017]. Therefore, we combined various sets of sieves, with or without the maximum particle length, and assessed the impact on MPS measurements.…”

Dust affects chewing efficiency and tooth wear in forest dwelling Western chimpanzees (Pan troglodytesverus)

“…Also in geladas, Venkatamaran et al () observed that older individuals had larger FPS indicating lower chewing efficiency than younger individuals, particularly during the dry season. Moreover, Weary, Wrangham, and Clauss () found an effect of seasonality (dry vs. wet), though not of age, on FPS in frugivorous Eastern chimpanzees ( Pan troglodytes schweinfurthii ). These authors hypothesized that the mainly frugivorous diet may be mechanically less challenging compared to the more folivorous diet of geladas.…”