. Bulletins of American paleontology. MoLLUSKS: Jackson et al. 205 1000. 100 1000 10000 Number of Specimens Text-figure 13.—Numbers of genera or subgenera versus numbers of specimens for the 37 faunules listed by the same numbers in Table 3. ters Oi" section, were treated as a single horizon. Near- by but physically separate outcrops of the same strati- graphic horizon were treated as separate faunules for purposes of replication in the analyses. Examples of replicate faunules include exposures on different head- lands of the Ma horizon of the Cayo Agua Formation (Faunules 16, 22,
. Bulletins of American paleontology. MoLLUSKS: Jackson et al. 205 1000. 100 1000 10000 Number of Specimens Text-figure 13.—Numbers of genera or subgenera versus numbers of specimens for the 37 faunules listed by the same numbers in Table 3. ters Oi" section, were treated as a single horizon. Near- by but physically separate outcrops of the same strati- graphic horizon were treated as separate faunules for purposes of replication in the analyses. Examples of replicate faunules include exposures on different head- lands of the Ma horizon of the Cayo Agua Formation (Faunules 16, 22, 23 and 24) or the Ma horizon of the Gatun Formation (Faunules 35 and 36) (Text-figs. 4, 5). The mollusks contained in the 37 faunules range from a minimum of 91 to a maximum of 18,181 spec- imens, and from 39 to 304 genera or subgenera (me- dians: 1723 specimens and 124 subgenera per faunule: Table 3). These numbers are large enough to include all of the faunules in analyses of faunal patterns in space and time. Nevertheless, most of this variation in numbers of specimens and taxa is still due to differ- ences in sampling effort, as demonstrated by the high- ly significant positive correlation between numbers of taxa and specimens among the 37 faunules (Spearman rank order correlation, r = +, P (Hayek and Buzas, 1997). This was always true for our data. Estimates of alpha for faunules and one-million-year intervals with fewer than 5000 specimens were obtained from Appendix 4 in Hayek and Buzas (1997). Estimates for those with more than 5000 specimens were kindly provided by Lee-Ann Hayek (written commun., 1997, 1998). Values of alpha for the 37 faunules range more than six-fold, from a low of at Chocolate Buenos Aires to a high of 67 at lower Lomas del Mar (median for the 37 faunules = ; Table 3). Alpha is positively correlated with the number of specimens in the faun- ules (Spearman rank-order correlation, r = +, P = ), but not so strong
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