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Group Formation of Reef Fishes Induced Through Food Provisioning

1980; Wiley; Volume: 12; Issue: 4 Linguagem: Inglês

10.2307/2387699

1744-7429

Murray Itzkowitz,

Animal Behavior and Reproduction

Group formation of foraging reef fishes was induced with different quantities of preferred food: the algae that covers dead staghorn coral (Acropora cervicornis). The speed at which a species finds the food depends on its basic search patterns. Once a food patch is discovered, all species rapidly converge on the source, suggesting that individuals gain foraging cues (e.g., visual and auditory) from both conspecifics and other species. The largest food sources do produce the largest groups, but this result appears to be a product of increased group stability rather than an increase in the total numbers of fishes in the area. IN A PREVIOUS STUDY (Itzkowitz 1977) I described the foraging patterns of mixed-species groups of reef fishes found over the shallow back-reefs in Jamaica. Two foraging patterns were observed and named the striped-parrot and the stoplight-parrot strategies. Those species that use the striped-parrot strategy readily join others engaged in feeding, but seem to have minimal cohesiveness and such groups rapidly disband. The stoplight-parrot strategy is used by solitary foraging species that usually join other species when attempting to pass through open areas. The striped-parrot strategy utilizes rapid consecutive nips on the substratum with little search behavior between nips, while the stoplight-parrot strategy utilizes single nips preceded by an obvious search of the substratum. While it seemed clear that widely dispersed food patches, hidden in crevices, controlled the foraging behavior of individuals using the stoplight-parrot strategy, those factors controlling the rapid nipping of the striped-parrot strategy were less clear (Itzkowitz 1977). I hypothesized that rapid nipping, without search behavior, suggested a uniformly distributed resource. This resource was probably of low quality since the time spent in any location was brief. The frequent position changes seemed designed to take advantage of randomly occurring food patches without sacrificing the ever-present poor-quality resource. The high probability of joining other species seemed to be a system of checking the food source of others. If the neighbor's food was poor, the individual might feed briefly and then leave (the commonly observed pattern). If the normally occurring pattern of small shifting groups with rapid compositional changes has evolved to exploit uneven rich food patches, the discovery of such a patch should alter the group dynamics of those utilizing the striped-parrot strategy. I predicted that not only would group size increase, but the time to discover such a patch would be different due to species using the striped-parrot versus stoplight-parrot strategies. These hypotheses and others were tested using artificially placed rich food patches. These experiments varied the size of the patch and the quantity of food, because a substantial literature has accumulated suggesting that these variables are influential in the composition of foraging groups (e.g., Altman 1974, Caraco and Wolf 1975, Jarman 1974).