Abstract
Animals are often in competition with other members of the same population. They compete over access to resources such as food, mates and breeding sites. Even parents compete with each other over who should provide care for their common young. When there is competition the fitness of one member of the population usually depends on the behavioural strategies adopted by others. In such circumstances the evolutionary endpoints can be characterised using evolutionary game theory. However, uses of game theory in behavioural ecology often ignore differences between individuals. Using a series of examples I will demonstrate that such differences are not innocuous noise, but can fundamentally change the nature of a game.
Differences promote the need to negotiate rather than make blind decisions, and the decisions reached as a result of negotiation may be very different to the decisions that evolve when individuals ignore information about others.
Once there are mechanisms that maintain variation within populations, such as mutation, the direction of evolution can depend on the amount of variation. Furthermore, when there are markets, so that individuals can break off interactions to seek a better partner, variation levels can interact with lifespan to determine how cooperative individuals are with each other.
Differences in personality promote the need to be socially sensitive. Social sensitivity changes the selection pressure acting on individuals who are observed, and can lead to the maintenance of differences. In other words the existence of differences can change the fitness landscape so that differences are maintained.