RESOURCE AND HABITAT SHARING BY THE STOPLIGHT PARROTFISH, SPARISOMA VIRIDE, A CARIBBEAN REEF HERBIVORE

We compare the vertical distribution, substrate preferences, grazing b ehaviour and social interactions of the stoplight parrotfish, Sparisom a viride, with that of other scarids at a fringing reef off Bonaire (N etherlands Antilles). Earlier reports that S. viride only displays ter ritorial behaviour against conspecifics are confirmed by the non-aggre ssive nature of this parrotfish and the low time expenditure on intera ctions with other herbivores. The vertical distribution of S. viride i s largely identical to that of several other scarids, acanthurids and pomacentrids, whose ranges may completely coincide with S. viride terr itories. Comparison, of the substrate use of the five most common scar ids inside a single S. viride territory yields no evidence of food par titioning. We suggest that the lack of interspecific territorial behav iour in S. viride is explained by the inability to economically defend a territory against all potential food competitors. Factors that may favour territory sharing between herbivores are fine-scale resource pa rtitioning and shared defence, both of which would reduce the costs of territorial life. However, more detailed investigation of herbivore f ood selection is required before definite conclusions can be drawn.