Ecology of female social relationships: Hanuman langurs (Presbytis entellus) and the van Schaik model.

The ecological model of Carel van Schaik provides clear predictions for female-female relationships in relation to scramble or contest within-group competition and contest between-group competition. These predictions were applied to data from a 12-year field study on Hanuman langurs (Presbytis entellus) that ranged freely around Jodhpur (India). It appears that hierarchical relationships between females (unstable, inconsistent, individualistic, with low rates of agonistic coalitions) reflect scramble within-group competition. Such competition, however, results in individual evolutionary advantages (differential feeding time; differential reproductive success) so that dominance effects mirror contest within-group competition. Between-group contest competition at Jodhpur is strong (low predator pressure, high population density, good food defensibility, essential role of females during intergroup encounters, loud vocalization of males). The results are discussed in the light of langur feeding habits.