Alternative methods of measuring competition applied to two Australian hermit crabs.

This article describes the intertidal hermit crab species assemblage at One Tree Island, Great Barrier Reef, Australia. Competition for shells between the two most abundant species, Clibanarius virescens and Calcinus latens, is studied in more detail. Competition appears to be primarily exploitative. The relative intensities of inter- and intra-specific competition between this pair of species are estimated using two different methods. The first is based on habitat overlap data in conjunction with a mathematical model of shell population dynamics described in Abrams (1980). The second method is more direct, and is based on following the fate of marked empty shells. Results of the two methods are very similar. This supports the validity of assumptions made in applying the first method. The relative amount of interspecific competition between these two species appears to be greater than that for other hermit crab species pairs studied previously.