Size-frequency and population structure of brachiopods |
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Authors: | Charles W Thayer |
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Institution: | Department of Geology, University of Pennsylavania, Philadelphia, Pa. U.S.A. |
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Abstract: | The living terebratulids, Terabratulina unguicula, Terebratalia transversa, Laqueus vancouverensis, and the rhynchonelid Hemithiris psittacea were studied in the San Juan Islands, Washington, U.S.A. Those results and a review of a the literature lead to the conclusion that most brachiopod populations experience episodic recruitment at intervals which may be irregular. The occurrence of juveniles attached to adults, brooding, and bi- or multimodal size-frequency distributions demonstrate that, contrary to a previously suggested hypothesis, adult brachiopods do not generally exclude juveniles from the same area. The commony observed rarity of small individuals is regarded as a product of local recruitment failure due to patchy distribution of larvae; it does not justify the assumption that brachiopods are unaffected by high post-larval juvenile mortality. However, the frequent rarity of small individuals confirms that this cannot be used as a criterion of transport in assemblages of fossil brachiopods. |
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