The result of gregariousness. The main factors affecting group living are food and predation. Foraging may be enhanced if members of a group inform each other about the whereabouts of food, and may be rendered more efficient by cooperative behaviour. On the other hand, if food availability is restricted, then there may be competition for food, if the group it too large, and there may be a disturbance effect during foraging. Thus redshank (Tringa totanus) are more likely to disturb each -other's shrimp (Corophium spp.) prey, if they feed in a large group. This happens because the birds' footsteps trigger the shrimps' retreat behaviour.
A specific advantage of living in a group is increased vigilance against predators. Many predators rely on an element of surprise to catch their prey, so constant vigilance is a good insurance against predation. Feeding efficiency is reduced if the individual spends too much time watching out for predators, but an individual in a group can, to some extent, rely on the vigilance of others. Another advantage of group living is the dilution effect. By joining a group, an individual dilutes the effect of a successful attack by a predator, because there is a chance (depending upon group size) that another individual may be the victim. Horses (Equidae) in the Camargue are less likely to be attacked by flies, if they are in a large group. Disadvantages of group living may include competition for mates and increased parasitism.
Subjects: Zoology and Animal Sciences — Evolutionary Biology.