Fiddler Crab Behavioral Ecology: Burrow Density in Uca Pugnax (Smith) and Uca Pugilator (Bosc) (Decapoda Brachyura)

Of three species oi fiddler crabs found in the salt marshes on Sapelo Island, Georgia, U.S.A., Teal (1958) has shown that Uca pugnax is the most widespread in distribution, and when paired with U. pugilator causes a reduction in the number of burrows dug. This field study examined burrow density in order to understand why burrow reduction occurs when U. pugnax is the interfering species. Populations of U. pugnax are seven times more dense than populations of U. pugilator, which appear to migrate periodically. In mixed populations of U. pugnax and U. pugilator the number of burrows dug by both species together is less than would be predicted by either alone. These data suggest that U. pugnax has a higher tolerance to crowding, and coupled with its widespread distribution and agonistic behavior, is better adapted to live under conditions unfavorable for other Uca species. U. pugilator exhibits greater behavioral variability which would have survival advantage since this species appears to migrate periodically to different environments once certain density levels are reached.