SUBORDINATE GROUP MEMBERS ACT AS FOOD-FINDERS WITHIN STRIPED PARROTFISH TERRITORIES

Female striped parrotfish Scarus iserti (Block) defend small feeding territories from conspecifics. Within these, large territorial individuals typically tolerate several smaller fish, perhaps because subordinate group members hasten the dominant's detection of good food patches. To test this idea, naturally occurring groups of striped parrotfish were presented with small patches of high quality food in a series of controlled experiments. Overall, time to patch discovery was inversely related to group size as was the time to discovery by the dominant fish. In addition, dominant fish had priority of access to patches once they were discovered. Thus, in the presence of subordinates, dominant striped parrotfish found and exploited rich food patches faster. This advantage apparently offsets the costs of resource depletion that subordinate group members represent and has ultimately contributed to both the formation and persistence of these stable territorial groups.