黔西北晚奥陶世Dalmanella testudinaria及Dorytreta longicrura(腕足类)居群动态学研究

对黔西北仁怀核桃湾、毕节燕子日晚奥陶世Ｈｉｒｎａｎｔｉａ动物群中Ｄａｌｍａｎｅｌｌａｔｅｓｔｕｄｉｎａｒｉａ及Ｄｏｒｙｔｒｅｔａｌｏｎｇｉｃｒｕｒａ居群的埋藏和时间均化的研究表明，两地居群均属原地埋藏的正常居群，且未遭受选择性破坏，这些化石居群的特征基本反映了原先生活居群长期变化的特征。它们的大小频率分布图是强烈的左偏斜，幼年期个体占很大比例。对各居群生存曲线的对比研究表明，生存曲线近似于Ｓ形（ｓｉｇｍｏｉｄａｌｔｙｎｅ），反映出幼年期死亡率很高，成年期死亡率较低，而老年期死亡率又增高。同一环境中Ｄａｌｍａｎｅｌｌａｔｅｓｔｕｄｉｎａｒｉａ居群的幼年期死亡率高于Ｄｏｒｙｔｒｅｔａｌｏｎｇｉｃｒｕｒａ居群，反映了物种自身的不同特性；另一方面，前述两种居群在核桃湾的幼年期死亡率高于在燕子口的幼年期死亡率，说明两地生活环境存在差异；物种分异度分析及剖面的微相分析表明，核桃湾古海水深度浅于燕子口。从大小频率分布图获得生存曲线时，宜采用Ｌｅｖｉｎｔｏｎ和Ｂａｍｂａｃｈ（１９７）的方法，即根据公式Ｄ＝ｓ×ｉｎ（Ｔ＋１）将大小转化为生存时限，而不宜采用Ｔｈａｙｅｒ（１９７７）的方法，即直接对作为横坐标的大小取对数。

POPULATION DYNAMICS OF DALMANELLA TESTUDINARIA AND DORYTRETA LONGICRURA (BRACHIOPODS) OF LATE ORDOVICIAN HIRNANTIA FAUNA FROM NORTHWESTERN GUIZHOU, SW CHINA

Populations of Dalmanella testudinaria and DOrytreta longicrara of the Hirnantt'a fauna from the Kuanyinchiao beds (Ashgillian) of Hetaowan, Renhuai County, and Yanzikou, Bine County, northwestern Guizhou, are time--averaged in situ normal populations,without selective destruction or dissolution, and their survivorship patterns represent thepatterns of their formal living populations. The size--frequency distributions of the abovepopulations with abundant juveniles are all left-skeweds their survivorship curves are ofthe sigmoidal type, i. e. with high juvenile mortality followed by a decline in youth andmaturity, to an increase again in old age. A comparison of the survivorship curves showsthat: 1)The juvenile mortality of Dalmanella testudinaria is higher than that of hotretalongl'crsra either at Hetaowan or at Yanzikou, reflecting a proper intrinsic nature of thesetwo species 1 and 2)The juvenile mortality of populations in Hetaowan is biger than that inYanzikou, indicating the difference of paleoenvironments at the two localities. The difference can be verified from species diversity as well as micro factes analysis. It shows the seawater was shallower at Hetaowan than at Yanzikou. In the construction of a survivorshipcurve from a size--frequency distribution,the author suggests strongly to follow the methodof Levinton and Bambach (1970) (i. e. using the equation D~s X In (T+ 1 ) ) rather thanthe method proposed by Thayer (1977) (i. e. plotting the log of size on the horizontalaxis).