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Open Access Publications from the University of California

The Effects of Density on Intraspecific Aggression in the Fiddler Crab, Uca crassipes, on Mo'orea, French Polynesia


Uca crassipes (Adams and White 1848) is one of two species of fiddler crabs found on Mo’orea, French Polynesia. Much like other animal populations, U. crassipes is subject to density dependent processes, such as competition, which increase with density. To better understand the relationship between competition and density, this study first looked at habitat differences between 8 distinct populations of U. crasspies on Mo’orea. It then explored differences in aggressive interactions between crabs at one high-density and one low-density site. In the field, both male and female fiddler crabs were found to fight more in the high-density population. Subsequent investigation of the effect of density on aggression in laboratory settings did not yield significant results. Though laboratory results were not significant, trends in data showed more fighting under high-density conditions. Further investigation is necessary to fully understand the effects of density dependent processes on fiddler crabs in both a field and laboratory setting.

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