A theoretical exploration of antipredatory and foraging factors promoting phenotype-assorted fish schools

We explore factors promoting phenotype-assorted schooling in fish. Since predator avoidance and food-finding are frequently stated as the evolutionary keys for group-living they shall serve as our framework. If individuals differ in appearance and predators have a preference for a given prey type, assorting into groups of matching individuals reduces the risk of predation. When considering foraging, individuals may differ in their abilities to find and share the prey. The effect of these characters on group-formation is examined. With differences in foraging ability it is likely that foraging groups become assorted. When fish numbers are low and costs of school swapping are high, assorted schools emerge. With increasing fish numbers, assorted schools are found only when school-shuttling costs are modest. The degree of phenotype segregation is dependent on the food-finding and food-sharing characters of individuals in the population, large differences promoting assortative schooling.