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).