Anti-predator function of bluegill sunfish nesting colonies

Abstract

Although the adaptive significance of nesting in colonies has been investigated repeatedly in avian species, until now no detailed studies have been reported on colonial nesting in fishes. Investigators of avian colonial systems have suggested that birds nest in colonies either as a response to predators^1,2 or to locate more easily ephemeral food resources^3,4. The avian literature is unclear, however, as to which selective pressure (predation or food resources) is more crucial, with investigators using similar evidence to reach essentially opposite conclusions⁵. I report here evidence obtained from a long-term study of a colonial fish, the bluegill sunfish (Lepomis macrochirus), showing extreme synchrony in breeding and the additional protection afforded offspring by tightly clustered groups of adults, which argues strongly that colonial nesting in this species and other fishes has evolved in response to predation pressure.