A test of the model of the economic defendability of a resource and territoriality using youngEtroplus maculatus andPelmatochromis subocellatus kribensis

YoungEtroplus maculatus andPelmatochromis subocellatus kribensis were reared on diets of low, medium, or high quantities of food and the ontogeny of behavior documented until fish matured. Data were categorized into: (1) from the beginning of the experiment to the midpoint (100 days forE. maculatus and 118 days forP. s. kribensis); and (2) from the midpoint to maturity. For both species the tendency to be territorial, as deduced by the numbers of territories defended, or number of charges or rams performed, was explained by a unimodal relationship between territorial tendency and food available per gram of fish. Young fish receiving low quantities of food were highly territorial, but as they grew and food available per gram of fish decreased, they gave up territorial behavior. Young fish receiving high quantities of food were not territorial initially, but as they grew became increasingly territorial. Fish receiving intermediate quantities of food always defended territories. Lateral displays were performed most often by fish receiving intermediate quantities of food apparently because they were ambivalent being close to either the lower or upper thresholds for territoriality.