Global taxonomic richness is affected by variation in three components: within-community, or alpha, diversity; between-community, or beta, diversity; and between-region, or gamma, diversity. A data set consisting of 505 faunal lists distributed among 40 stratigraphic intervals and six environmental zones was used to investigate how variation in alpha and beta diversity influenced global diversity through the Paleozoic, and especially during the Ordovician radiations. As first shown by Bambach (1977), alpha diversity increased by 50 to 70 percent in offshore marine environments during the Ordovician and then remained essentially constant for the remainder of the Paleozoic. The increase is insufficient, however, to account for the 300 percent rise observed in global generic diversity. It is shown that beta diversity among level, soft-bottom communities also increased significantly during the early Paleozoic. This change is related to enhanced habitat selection, and presumably increased overall specialization, among diversifying taxa during the Ordovician radiations. Combined with alpha diversity, the measured change in beta diversity still accounts for only about half of the increase in global diversity. Other sources of increase are probably not related to variation in gamma diversity but rather to appearance and/or expansion of organic reefs, hardground communities, bryozoan thickets, and crinoid gardens during the Ordovician.

中文翻译：

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阿尔法、贝塔或伽马：所有的多样性都去哪儿了？

全球分类丰富度受三个组成部分变化的影响：群落内或阿尔法多样性；社区间或 beta 多样性；以及区域间或伽马多样性。一个由分布在 40 个地层间隔和 6 个环境带中的 505 个动物群组成的数据集用于研究 α 和 β 多样性的变化如何影响古生代的全球多样性，特别是在奥陶纪辐射期间。正如 Bambach (1977) 首次表明的那样，奥陶纪近海海洋环境中的 α 多样性增加了 50% 到 70%，然后在古生代的其余时间基本保持不变。然而，这一增长不足以解释在全球通用多样性中观察到的 300% 的增长。结果表明，水平间的β多样性，早古生代软底群落也显着增加。这种变化与奥陶纪辐射期间多样化分类群的栖息地选择增强有关，并且可能增加了整体专业化。结合α多样性，β多样性的测量变化仍然只占全球多样性增加的一半左右。其他增加的来源可能与伽马多样性的变化无关，而是与奥陶纪有机礁、硬地群落、苔藓虫灌丛和海百合花园的出现和/或扩张有关。结合α多样性，β多样性的测量变化仍然只占全球多样性增加的一半左右。其他增加的来源可能与伽马多样性的变化无关，而是与奥陶纪有机礁、硬地群落、苔藓虫灌丛和海百合花园的出现和/或扩张有关。结合α多样性，β多样性的测量变化仍然只占全球多样性增加的一半左右。其他增加的来源可能与伽马多样性的变化无关，而是与奥陶纪有机礁、硬地群落、苔藓虫灌丛和海百合花园的出现和/或扩张有关。