Size-Frequency Distributions in Decapod Crustacea: The Quick, the Dead, and the Cast-Offs

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Abstract
A consideration of size-frequency distributions of fossil trilobite assemblages indicated that accumulated exuviae will have a different size-frequency distribution than the living population from which they were derived. This concept was examined in more detail for a population model of an extant crab species, using published data on molt increment and intermolt period, and making assumptions on mortality rates. The size-frequency distribution for living crabs resembles a normal curve (except for high abundance in very small size classes). The size-frequency distribution for corpses, exuviae, or combinations of these two, all show a steady decline with size. Very different mortality assumptions were applied to the model and the conclusion regarding exuviae was found to be robust. Thus, the size-frequency distributions of fossil arthropod assemblages, or of exuviae of living species, cannot be expected to resemble living population structures.

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