Social dynamics of mixed-species groups of Jamaican reef fishes

Abstract

1. Observation of coral reef fish in Jamaica revealed a continuous and erratic series of fluctuations in both individual and species group size. 2. No apparent trend existed between group size or species composition with any subsequent changes in the group. However, solitary striped parrots did, eventually, join conspecifics and very large groups fragmented. Other species (i.e., redtail parrot, ocean surgeon, blue tang, spotted goatfish, and foureye buttefly fish) did join the striped parrot groups for brief periods and tended to be solitary for long periods of time. 3. The rapid compositional changes were attributed to the different foraging strategies of the component species. Two basic strategies were identified; the striped parrot and the stoplight parrot strategies. Both herbivores and carnivores occurred in each strategy. 4. Species utilizing the striped parrot strategy (e.g., striped parrot, blue tang, ocean surgeon, and spotted goatfish) fed in open areas of sand, grass, and/or small rubble. The feeding behavior consisted of rapid, consecutive nips at the substrate with little time invested searching for food once the animal settled to the substrate. 5. Species utilizing the stoplight parrot strategy (e.g., stoplight parrot, redtail parrot, and the foureye butterfly fish) appeared to carefully search the crevices or the surfaces before making a nip. Multiple nips usually contained search time between each nip. 6. The species utilizing the striped parrot strategy formed and disbanded in the open areas and appeared to forage on a homogenuous resource. An individual joined others already engaged in foraging and fed only within its immediate area of settlement. Once food was exhausted, it left the group and joined another or began foraging on its own. 7. The species using the stoplight parrot strategy moved from one patchy resource to another and joined groups mainly as they passed through the open areas. 8. The mixed-species groups were products of seemingly random encounters between species having different foraging strategies.