We determined the dominance hierarchy in competition for refuges by the xanthid crabs Panopeus simpsoni, Eurypanopeus depressus, Rhithropanopeus harrisii, and juvenile Callinectes sapidus, and used it to predict predation risk from adult blue crabs in laboratory experiments at two salinities. Experiments were first run with pairwise combinations of species with limited refuges. To determine any effects of diffuse competition on dominance and predation risk, all four species were then held together with limited refuges. The same process was then repeated in experiments with a blue crab predator, again with limited refuges. Juvenile C. sapidus and E. depressus were dominant over P. simpsoni and R. harrisii in occupying shelters at both salinities, in both paired- and multiple-species combinations. Dominance in refuge use increased with salinity in C. sapidus, E. depressus, and P. simpsoni, but not in R. harrisii. Because they were more dominant, C. sapidus and E. depressus sustained lower mortality to predation than P. simpsoni, and R. harrisii. Furthermore, field sampling indicated the least dominant species, R. harrisii, was common only in low-salinity areas with few predators. The greater dominance of C. sapidus and E. depressus may thus decrease their predation risk in estuarine waters and explain their broader distribution across salinities.
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Vol. 30 • No. 3