Table 1.

Summary of potential costs and benefits of among-group assortment for individuals based on physiological traits (i.e. uniformity of a given physiological trait within fish schools).

ecological context	benefits	costs
predator avoidance/foraging	decreased oddity effect under predatory attacks increased information transfer and synchrony during coordinated escapes similar energy and nutritional requirements, thus group members spend the same amount of time foraging and searching for similar food sources	increased foraging competition among individuals with similar metabolic demand, increased aggression reduced chance to outpace group-mates when fleeing predators for high-performance phenotypes increased number of individuals required for optimal group size for low-performance phenotypes
group composition	increased cohesion in moving groups if all members have same swimming ability similar environmental tolerances and responses to stressors and so reduced exposure to non-optimal environments when conforming to group behaviour	decreased ability to occupy preferred spatial position within group; possible within group competition for spatial locations decreased niche differentiation within group (i.e. many fish may compete to be leaders in groups of high-performance individuals), possibly reducing group cohesion
resource allocation	minimize energy expenditure if all fish have similar optimal swimming speed for low-performance phenotypes, matching behaviour of group may decrease energy allocation to activity and to somatic growth and more to reproduction	higher competition for preferred position can increase shuffling rate while swimming, thus energy expenditure for high-performance phenotypes, matching behaviour of group-mates may increase energy allocation to activity and somatic growth, thus decreasing reproductive allocation