Predation and primate cognitive evolution

Predation is a major cause of mortality in non-human primates (Cheney et al., 2004), but its impact as a selective force on primate evolution is not well understood. Predation has long been thought to affect traits such as body size, group size, group composition, and ecological niche, as well as the traits of vigilance and vocal and reproductive behaviour (Anderson, 1986). The general assumption is that if a trait has evolved as an adaptation to predation, then there should be a negative relationship between the expression of the trait and the individual’s vulnerability to predation. First, if large body size is an adaptation to predation (Isbell, 1994), then larger primates should be underrepresented in a predator’s prey spectrum compared to smaller ones. Second, if individuals living in large groups are less susceptible to a certain kind of predation, leopard predation, for example, due to enhanced levels of predator vigilance, then individuals of larger groups should be underrepresented in the prey spectrum (van Schaik, 1983; Cords, 1990). Third, if multi-male groups are an adaptation to predation, for example due to the possibility of cooperative defence (Stanford, 1998), then species living in multi-male groups should be underrepresented in a predator’s prey spectrum compared to single-male groups. Fourth, if females shorten their inter-birth intervals to increase their lifetime reproductive success to compensate for higher levels of predation (Hill & Dunbar, 1998), then individuals with short inter-birth intervals should be over-represented in the prey spectrum.