Another possible benefit of aggregation is to protect against predation by group anti-predator behavior. Many species exhibit higher rates of predator vigilance behavior per individual at lower density. This increased vigilance might result in less time and energy spent on foraging, thus reducing the fitness of an individual living in smaller groups. One striking example of such shared vigilance is exhibited by meerkats. Meanwhile, other species move in synchrony to confuse and avoid predators such as schools of sardines and flocks of starlings. The confusion effect that this herding behavior would have on predators will be more effective when more individuals are present.Cooperative feeding
Context: In the sub-Saharan African country of Nigeria, there are two main species that tend to travel in groups. The antelope tend to travel in groups in high numbers, and thus exhibit a high density. Meanwhile, the bison tend to travel in groups of small numbers, and therefore exhibit low density. Both the antelope and the bison have natural predators that exist in Nigeria.
Question: Individuals from which species, the antelope or the bison, will have higher rates of predator vigilance behavior?