Effect of Group Size on Time Budgets and Ranging Behavior of White-Headed Langurs in Limestone Forest, Southwest China

The ecological constraints model is well supported by data from most frugivorous primates; however, the prediction power of the model is weak for folivorous primates. From September 2016 to August 2017, we collected comparative data on time budgets, daily path lengths and diets of four groups of white-headed langurs (Trachypithecus leucocephalus), including two large groups (G-DS and G-ZWY) and two small groups (G-LZ and G-NN) in Chongzuo White-Headed Langur National Nature Reserve, Guangxi Province, Southwest China. The aim was to obtain evidence of foraging competition and to test the ecological constraints model on this highly folivorous primate in its karst habitat. The results showed that langurs in the larger groups spent more time traveling, less time resting, and had a longer average daily path length than those in the small groups. Diet composition and dietary diversity were not significantly different between the large and small groups. Our study demonstrates that langurs from large groups suffer scramble competition in limestone forests and supports the validity of the ecological constraints model for folivores.