Variation in Threespot Damselfish Aggression Using Models of a Conspecific, Predator, and Herbivore

The purpose of this research was to determine the level of defensive aggression of the threespot damselfish, Stagastes planifrons, when exposed to intruders of different species using models. Adult S. planifrons were exposed to models of a conspecific, an herbivorous fish, Sparisoma viride, and a predator, Aulostomus maculatus. Attack rates and retreat rates of S. planifrons were determined by observations during exposure to models. It was expected that aggression levels would be highest towards the conspecific model and lowest towards the predator model and that evasive behavior would be highest in the presence of the predator model and lowest with the conspecific. It was found that there is a significant difference in the level of aggression when encountering a predator versus a conspecific, showing more aggression towards the conspecific and more evasion towards the predator. No significant difference was found in the aggression levels shown between the predator and the herbivore. Exposure to the predator elicited the highest number of retreats, also showing a significant difference in the level of evasion when comparing all three models. The results suggest that S. planifrons are able to differentiate between intruder species and react depending on the level of threat posed and perhaps on what is most energy efficient.

This student research was retrieved from Physis: Journal of Marine Science III (Spring 2008)19: 13-18 from CIEE Bonaire.

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