Pair-bonding among nonhuman primates is rare and the possible selection pressures at work to maintain this type of social grouping have been discussed at great length (Kleiman, 1977; Wittenberger, 1980; Kinzey, 1987; Palombit, 1999; Fuentes, 1999, 2002; Chambers, 2002; Reichard, 2003; van Schaik and Kappeler, 2003). While the behavioral ecology of pair-bonded species has been relatively well studied across radiations, there are fewer studies that examine the nuances of social behavior between pair-bonded individuals and how social behavior is affected by ecological variables such as changes in food availability and feeding competition (but see Curtis and Zaramody, 1997; Bartlett, 2003; Fietz, 2003; Curtis, 2004; Schulke, 2003, 2005). This inhibits researchers’ ability to fully evaluate the two main competing hypotheses, mate defense and resource defense (Wrangham, 1980; Dunbar, 1988), that have been put forward to explain the evolution of pair-bonding. Of these two sets of hypotheses, mate defense models have received more attention and empirical support (van Schaik and Dunbar,