4.1 Dietary characteristics of the fragmented limestone-living François’ langur
Species foraging strategies are closely related to their behavior and ecological plasticity. The same species may adopt different foraging strategies in response to different habitats, which helps them adapt to changes in habitat quality due to different natural or anthropogenic disturbances. In this study, the François’ langur ate 101 plant species. When compared with three other different geographical populations of similar latitude and climatic conditions, the langurs living in ECNNR feed on more plant species (Nonggang: 84 species/90 species; Fusui: 56 species/51 species, Table 6), and their diet had a high diversity (3.08). This result did not support our first hypothesis. Previous studies have shown that there are significant differences in the diet of the different geographical populations of François’ langurs, and this difference is likely related to the local vegetation composition (Li et al., 2016). The results of this study support this finding. High-quality habitat often means more food variety but it can also result in a high abundance of a single plant species. Animals can adjust their diet according to their food preferences and consume more of their preferred plant species. This has been confirmed in other studies of colobus monkeys, where only some of the species are consumed despite the high diversity of the plant species in the forests. Similar conclusions have been found for other langurs; for instance, white-headed langurs (Trachypithecus leucocephalus Tan, 1957) selectively use some plants in their habitat (Zhang et al., 2017). However, when the number of preferred foods is insufficient, monkeys can expand their diets and eat more alternative foods to overcome the lack of their preferred foods (Zhou & Huang, 2021). The high level of food diversity in the ECNNR may also be evidence of this strategy. According to the vegetation survey, the diversity of the plant species in the study area reached 145 species/ha (DBH ≥ 5 cm). This is much larger than the abundance in Fusui of 70 species/ha (DBH ≥ 1.2 cm; Li et al., 2015). Thus, even though the habitats are extremely fragmented, many of the fragmented habitats may act as safe havens, where relatively rich vegetation conditions are preserved locally. This provides an adequate food source for the langurs. This suggests that François’ langurs not only have a wide dietary composition but can also adjust their dietary composition according to the differences in the plant species in the habitat, and foraging flexibility is one of the important reasons for their survival in various habitats (Garber et al., 2009; Chaves & Bicca-Marques, 2013).