Coral feeding butterflyfishes are appropriate subjects to test territorial energy maximiser models such as that of Hixon (1980). However, energy maximiser models typically include the assumption that food resources within territories are unaffected by predation. If this is not the case, and mean food availability depends upon the mean rate of food exploitation, maximum net food intake may vary with the food exploitation strategy adopted. Following the method of Hixon (1980), butterflyfish food intake is modelled under the assumptions that (a) coral resources respond to attack by becoming unavailable and recovering slowly over time and (b) butterflyfish occur in small groups that can fragment to reduce territory defence costs. The model predicts that group members should remain together in small territories, and separate in large territories. Field observations were consistent with assumptions (a) and (b). Field measurements of grouping behaviour of 12 species of corallivorous butterflyfishes are consistent with the predictions of the model. These results indicate that the renewal characteristics of coral food may be important when considering variation in butterflyfish social behaviour.
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