the benefit of information sharing via being vigilant and making alarm signals is sufficient to select for cooperative behavior in heterogeneous groups. This finding demonstrates that kinship is not necessary for cooperative behavior to evolve as long as there is some benefit to information sharing within the group, e.g., reducing predator attack efficiency. 

Further, our results point to a heretofore unsuspected cost of gregarious foraging that is unique to heterogeneous groups. We call this the “two-fold cost of vigilance.” In our model, vigilance behavior in heterogeneous groups is more than a trade-off with foraging on the individual level. By choosing to be vigilant, prey also risk aiding in the survival of rival prey, which then puts the vigilant prey at a fitness disadvantage because it sacrificed a round of foraging to aid the rival prey. Together, these costs could explain why prey in heterogeneous groups evolve to be less vigilant than those in homogeneous groups. 

At the same time, it is also possible that there are some evolutionary advantages unique to heterogenous groups that we have not yet addressed. For example, our model does not currently allow for any kind of specialization in roles between individuals, which could explain the presence of multi-species groups in nature [52, 53]. If the prey could evolve to preferentially pay attention to certain “sentinel” members of the population (who, in turn, choose to be vigilant nearly always in order to receive some form of rewards, e.g., food or increased social status) then perhaps an evolutionarily stable form of gregarious foraging could be found in heterogeneous groups of all sizes. It is even possible that such a complex social structure could out-perform the relatively primitive cooperation in our homogeneous groups. 

Alongside genetic relatedness, another positive selective pressure for the evolution of vig- ilance is a semelparous reproductive strategy. When prey must survive any and all predator attacks in order to reproduce, the impetus to be vigilant is much greater. Semelparous or- ganisms are known to be more risk-averse than similar, iteroparous organisms [54], and the decision to forage instead of being vigilant is an example of one such risky behavior. Thus, rather than spending most of their time foraging (as iteroparous prey evolve to do in our 

