4.3 Food choice
Previous studies have shown that primates are selective about the types and components of their food, including the selection of plant species and food portions (Zhou et al., 2018). This selectivity is influenced by factors, such as the quality and quantity of food (e.g., nutrients, cellulose, mineral elements, secondary toxicants, and food availability) and water content (Zhou et al., 2021). The findings of this study were consistent with previous studies, and the Encheng François’ langur had obvious food selectivity. However, food selection is not strictly based on the number of plants in the habitat. In this study, 72.99% of the total foraging records of the François’ langurs consisted of 23 plant species. They used 68 of the 150 plant species marked by the vegetation surveys in the overall foraging record, which accounted for 89.04% of the total foraging record. The top 10 tree species in the vegetation survey included Pittosporum pulchrum and Vitex kwangsiensis, which accounted for more than 2% of the total foraging records. This was similar to the findings of other studies. In the Van Long Nature Reserve in Vietnam, the 10 most commonly consumed plants by Trachypithecus delacouri accounted for 82% of the total foraging records (Workman, 2010). In Madhupur, Bangladesh, the caped langur (Trachypithecus pileatus (Blyth, 1843)) feeds on only 35 species of trees and vines during the year (John et al., 2001). In Sri Lanka, long-tailed langurs used a total of 43 plant species, of which 70% of their food consisted of 10 species, none of which were dominant species (Newton, 1992). In the Kuala Lumpur area, 45% of the diet of the black-crowned langur consists of five plant species, which make up only 9.6% of the forest tree species (Bennett, 1983). François’ langurs and white-headed langurs showed selectivity in the plant species they ate, and the 10 plants that were most consumed accounted for 51%–90% of the food composition (Zhou & Huang, 2021). In summary, François’ langurs living in the ECNNR have similar feeding behaviors to other primates, their choice of food is independent of the number of plant species in the habitat, and the most common tree species in the habitat are only consumed in a small amount.
Overall, we found the François’ langurs in the fragmented limestone forest in southwest China had a similar feeding ecology to other François’ langurs in distinct habitats. However, there were also some differences. The langurs in this study ate a higher number of food species throughout the year when compared with other species, maintained a high level of food diversity, and ate more vines. These François’ langurs might have a slightly different feeding strategy than the other François’ langur populations, although we suspect that these dietary differences are mainly due to environmental conditions. We concluded that François’ langurs exhibit a flexible feeding strategy, and thus they are an ecological generalist that inhabits fragmented limestone forests. Further research is needed to better understand the langurs’ feeding ecology, especially in southwest China.

CRediT authorship contribution statement

Qi-Hai Zhou and Peng-Lai Fan conceived the ideas and designed methodology; Wei Yao, Jia-Xin Zhao, Rong Huang, Wen-Hua Li collected the data; Wei Yao and Cheng-Ming Huang analysed the data and wrote the manuscript. All authors contributed critically to the draft and gave final approval for publication.