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Morphological Variation of the Foraminifer Ammonia Becarrii (Linne)

其他書名	From the Atlantic Coast of the United States
出版	University of Kansas Paleontological Institute, 1974
URL	http://books.google.com.hk/books?id=P6tojgEACAAJ&hl=&source=gbs_api

註釋"The foraminifer Ammonia beccarii (Linné) was studied from various Holocene environments of the Atlantic coast of the United States in order to define its morphological variation and to determine the possible causes of the variation. At the beginning of the study, 45 morphological characters were measured from each of 221 specimens from two areas located in the northern and the southern portions of the coast. Comparison of characters indicated that many of the characters are intercorrelated, and each character has different significance in revealing the geographical variation of morphology. After elimination of the correlated characters and the nonsignificant characters, eight characters were considered sufficient to describe the morphology of the animal. Using these eight characters, the average sample size necessary for discrimination among samples from different environments was estimated to be about 30 specimens per sample. Based on the guidelines given by the above study, 25 samples from the coast were used for studying geographical variation of the morphology. The sample sizes ranged from 6 to 56. Each specimen was measured for its eight selected characters. Statistical analysis showed that among the characters measured, proloculus size and umbilicus size have relatively large variation among samples and small variation within samples. Evidently these two characters are the most useful in discrimination among samples from different areas. Further consideration of sample location suggested that there are two geographical varieties of the animal: one variety with large proloculus and large umbilicus existing north of Cape Hatteras, and the other variety with small proloculus and small umbilicus existing south of Cape Hatteras. The relationships of 14 environmental factors to morphological variation were studied. Two water masses separated by Cape Hatteras were shown to be the most important factors affecting the morphological variation. Five other important factors are runoff from land, sediment size, macrohabitat, tidal range, and winter climate as measured by annual snowfall. The macrohabitats considered include estuary, bay, tide pool, and open sea. Actually these five factors represent local conditions, which modify regional characteristics of the water mass and cause some variation of the morphology."--Pg. [1].