The criteria in relation to which it is possible to determine which of a set of alternatives is the best. In animal behaviour studies, optimality criteria are usually framed in terms of fitness. The ideal criterion would be inclusive fitness but this is normally impractical. In most studies, some short-term index of fitness is employed as the optimality criterion. For example, in studies of foraging behaviour, the notion of profitability is often the criterion used to judge the best foraging strategy. In other types of study, the concept of utility is the optimality criterion.
Optimality criteria are important wherever there is a trade-off among the various costs and benefits of an activity. For example, a certain type of prey may be the most profitable for a foraging animal, but the time spent hunting that prey may also be time that the forager itself is exposed to predation. There is a trade-off between profitability and exposure time, in this case, and the optimality criteria must take into account both the energetic and the temporal aspects of foraging.
Optimality criteria may be employed to calculate the optimal behaviour strategy or optimal design (e.g. of a limb), but the optimal solution is not always a stable one. For example, there are advantages and disadvantages of living in groups, and it would seem to follow that there should be an optimal group size for a particular species. However, if there were a group of the optimal size, then it would pay a solitary individual to join the group, thus pushing the group above the optimal size. The optimal group is unstable, and a stable group will, in practice, tend to be larger than the optimum.
An evolutionarily stable strategy (ESS), in particular, cannot be an optimal strategy because, by definition, it cannot be bettered by any feasible alternative strategy, provided sufficient members of the population adopt it. ESSs are found in cases where the best strategy for an individual depends upon the strategies adopted by other members of the population.
Subjects: Zoology and Animal Sciences.