Ecological Cues and Experience Modify Interspecific Aggression By the Damselfish, Stegastes Fasciolatus

Stegastes fasciolatus is an omnivorous damselfish that feeds primarily on benthic filamentous algae. It defends an interspecific territory and selectively attacks potentially competitive herbivores. When captive individuals are exposed to the cichlid fish, Sarotherodon mossambica (tilapia), they show little aggression toward this predator-like species that they have never encountered. The hypothesis that S. fasciolatus learns to recognize competitor species based on their feeding habits was examined. Damselfish were exposed to tilapia that had been trained to feed like a herbivore or a zooplanktivore. Aggressive responses to tilapia and two species of surgeonfish competitors were observed before and after experience with tilapia. Experience with planktivore tilapia resulted in little change other than a possible reduction in aggression shown to tilapia. Experience with herbivore tilapia produced two types of changes: First, aggressiveness toward tilapia showed a general increase. Second, the spatial distribution of response and the effects of specific stimuli, especially feeding, showed a qualitative change toward that shown to surgeonfish. Conclusions were that experience with ecological cues can produce a perceptual change in that a new species is recognized as a competitor. However, the nature of the ecological cue could be either observation of feeding movements or actual competitive feeding. Incidental observations and tentative conclusions were drawn regarding serial territoriality and the relationship between the quality of a territory and the form of interspecific aggression. /// Stegastas fasciolatus ist ein allesfressender "Damselfish", der aber in erster Linie von Tiefwasseralgen lebt. Er verteidigt seinen Lebensraum und greift manchmal die anderen Pflanzenfresser an. Wenn eingefangene Fische dem Cichliden Sarotherodon mossambica (Tilapia) ausgesetzt sind, zeigen sie wenig Angriffslust gegen diese Raubfischart, die sie nie vorher kennengelernt hatten. Die Theorie, dass die S. fasciolatus ihre Konkurrenzarten an ihren Fressgewohnheiten erkennen, haben wir bereits untersucht. Damselfische wurden Tilapia ausgesetzt, die trainiert waren, wie Pflanzenfresser oder Planktonfresser zu leben. Das Maß der Angriffslust gegen diese Tilapia und 2 Arten "Surgeonfische" wurde beobachtet. Die Erfahrungen mit planktonfressenden Tilapia ergaben wenig Unterschiede, bis auf den Rückgang der Angriffslust gegen andere Tilapia. Erfahrungen mit pflanzenfressenden Tilap