It is generally assumed that the reason prey tend to be found in herd groups but large predators are more likely to be solitary or hierarchical is due to the fact that prey species gain protection from their group while predators only gain competition provided they can hunt sufficiently alone. Using computer simulations it is possible to show some evidence for this as evolution can be simulated. However these past models have almost been designed for showing the development of group formation and so have assumed their own conclusion. The models that don’t make this mistake often simplify the problem by assuming that only one type of predation occurs at any time although this is rarely true in the wild with species under attack from many different sources.
An improved computational system has recently been created which attempts to show how prey will have evolved with multiple threats present and what exact mechanism prey will have needed to evolve to remain in groups. When it comes down to the protection given by a group there are four main benefits. Being at the centre means that the attack domain is basically zero and even being at the edge cuts down the possible attacking directions by half. Being in a group can also be intimidating and confusing for predators as tracking any one animal becomes more difficult and the herd together has more risk of injuring any would be predator. Having more of your species present also means that the average scanning time of your surroundings between eating is decreased as you know any predator is likely to be spotted by one of your team mates. Finally the chance that you are the one picked out deceases massively when surrounded by other potential victims who are just as likely to be chosen. Of course depending on the programmed level of the predator these strategies become more and less effective. It was successfully shown in the model that even when eight different predator attack patterns were used the result was broadly the same but with some important subtleties. If the predators focus on lone prey then the species naturally forms herds, but if the predator deliberately targets groups, specifically the centre of groups, as a dispersing method then evolving herd instincts is not as common. In these latter cases a swarm structure rather then a herd is developed. Generally species do not evolve is such a black and white way and can switch between group strategies based on experience and likely predation techniques.