Aggressive interactions and food competition in relation to species displacement among crayfish of the genus Orconectes.

Abstract

Interactive aggression among crayfish was investigated in the stream habitat. Orconectes rusticus and O. propinquus were observed during three nights in the Pigeon River at point sources of food competition. They freely approached a circular arena produced by the diffuse illumination of a flashlight in a glass-bottomed bucket. Aggressive actions by any crayfish to another within the arena were recorded and counted. O. rusticus was observed to be more aggressive toward O. propinquus than toward other O. rusticus by average aggressive acts per interaction. O. propinquus dealt the fewest aggressive acts; O. propinquus was not observed aggressing against conspecifics. White light from the flashlight and the full moon may have deterred O. virilis from approaching the arena. O. rusticus was the most aggressive of the two species observed in the field.