4.2 Dietary response to phenology change
The quantity and quality of food resources are not always evenly
distributed in space and time (Fryxell, 1991). Seasonal changes in
temperature and precipitation often result in changes in primate
foraging strategies by altering the availability of food resources
(Oates, 1987). In this study, François’ langurs expanded their food
intake in the dry season (dry season: 44 species; rainy season: 33
species), which effectively alleviated the foraging pressure caused by
food scarcity. This may be a coping strategy for François’ langurs when
there is food scarcity. Therefore, François’ langurs broaden the
richness of their diet by increasing the food diversity and food variety
to get enough food. This finding is consistent with other studies (Li et
al., 2003). For instance, Luo (2000) found that in the Mayanghe area of
Guizhou, the François’ langurs fed on more food species in the spring
and autumn (42 species) than in the winter and summer (24 species). In
the Nonggang area of Guangxi, François’ langurs also increased the
number of foraging plant species during the dry season to cope with the
lack of their preferred food (Zhou et al., 2006). Additionally, in the
Chongzuo region of Guangxi, white-headed langurs increased their intake
of plant species during the dry season (Zhou & Huang, 2021), while in
Malaysia, Presbytis femoralis fed on more types of food during
the food shortage season (Bennett, 1983). This trait was also seen in
other food-eating primates, such as Lophocebus albigena , which
increased their food diversity during the months when the fruit
abundance was lower (John et al., 2001). These studies all supported the
suggestion that primates can survive periods of food scarcity by
adjusting the food diversity of their diet.
François’ langurs also survive long dry seasons by adjusting their food
composition (Zhou et al., 2018). The results of this study showed that
the François’ langurs increased their feeding on mature leaves when the
feed intake of the young leaves decreased during the dry season when
compared with that during the rainy season, and most of the seed and
bark records occurred in the dry season (seed: 100%, bark: 85.6%).
This was supported by other studies. According to Zhou et al. (2006),
during the dry season when the food was scarce, the Nonggang François’
langur consumed mature and young leaves as an alternative food to solely
young leaves. In Fusui, Li et al. (2009) found that François’ langurs
also increased their intake of mature leaves in the dry season. In
Chongzuo, Guangxi, white-headed langurs fed on more young leaves during
the dry season but increased their intake of mature leaves (Li &
Rogers, 2006). On the island of Kaba in Vietnam, Kaba langurs
(Trachypithecus delacouri (Osgood, 1932)) consumed more leaves
during the dry season and correspondingly reduced their fruit intake
(Workman, 2010). Moreover, the long-tailed langur (Semnopithecus
entellus (Dufresne, 1797)) in the Kanha region of India will eat mature
leaves in large quantities when there is a shortage of young leaves,
fruits, and flowers (Newton, 1992).