How diet composition, dietary toughness, age and sex influence fecal particle size in Yakushima Japanese macaques

抄録

Fecal particle size is a measurement of the result of chewing. It provides important information about the feeding and digestion of herbivores. Understanding the effects of the potential proximate determinants, such as age, sex, and dietary toughness, on fecal particle size helps us interpret this widely used measurement, but have not been extensively investigated, especially in primates. This study aims to clarify how these factors influence fecal particle size in omnivorous Yakushima Japanese macaques. We simultaneously documented their diet, food toughness, and fecal particle size in the lowland area of Yakushima in the period from March 2018 to April 2019. Fecal particle size showed limited differences across months and no difference among age-sex classes. Dietary toughness showed no effects on fecal particle size, while only the consumption of fruits showed a marginally significant negative effect. Our data indicate that food toughness did not limit food comminution in our study subjects, while no age-sex class showed a difference in chewing ability. The lack of variation might derive from a less tough diet compared to the gelada, in which an effect of toughness on fecal particle size was found. These results suggest that food comminution is less variable in frugivores and omnivores primates compare to highly specialized species (such as geladas). This study showed dietary toughness, age and sex differences not always result in fecal particle size variations in frugivores and omnivores species, while the physical structure of foods should be considered during interpreting relevant results.