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Dilution effect
The dilution effect is simply that the more individuals there are in a group, the smaller each individual's probability of getting attacked is.
An example of this is seen with Adélie Penguins. They are predated by Leopard Seals, which loiter around the edges of the ice formations where these penguins are found, so that when the penguins dive in the water to feed they ambush them. So, if the penguins wait until there is a big group of them, then they can all jump in together, reducing the risk of getting caught. Unfortunately, those that jump in first or last are most likely to get eaten.
Will Cresswell in 1994 observed and carried out experiments on Redshanks in mudflats and marshes in Scotland . He found that once flock sizes reach over 30 in number that each individual bird spent less than 2 seconds at a time being vigilant. He therefore realised that once communities reach a certain size, vigilance no longer has such a crucial effect on the community. He noticed that it actually became harder for an individual to be singled out by a predator for attack and some times it would even deter a predator. This is another good example of the dilution effect being seen in practice.
