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. 2001 May 22;98(11):6261-6.
doi: 10.1073/pnas.111144698. Epub 2001 May 15.

Effects of Sampling Standardization on Estimates of Phanerozoic Marine Diversification

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Free PMC article

Effects of Sampling Standardization on Estimates of Phanerozoic Marine Diversification

J Alroy et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Global diversity curves reflect more than just the number of taxa that have existed through time: they also mirror variation in the nature of the fossil record and the way the record is reported. These sampling effects are best quantified by assembling and analyzing large numbers of locality-specific biotic inventories. Here, we introduce a new database of this kind for the Phanerozoic fossil record of marine invertebrates. We apply four substantially distinct analytical methods that estimate taxonomic diversity by quantifying and correcting for variation through time in the number and nature of inventories. Variation introduced by the use of two dramatically different counting protocols also is explored. We present sampling-standardized diversity estimates for two long intervals that sum to 300 Myr (Middle Ordovician-Carboniferous; Late Jurassic-Paleogene). Our new curves differ considerably from traditional, synoptic curves. For example, some of them imply unexpectedly low late Cretaceous and early Tertiary diversity levels. However, such factors as the current emphasis in the database on North America and Europe still obscure our view of the global history of marine biodiversity. These limitations will be addressed as the database and methods are refined.

Figures

Figure 1
Figure 1
Genus-level diversity curves for the two study intervals based on Sepkoski's widely cited, unpublished global synoptic compilation (7, 8). This data set attempts to capture all published information on first and last appearances through time. The current version includes 29,773 genera of marine animals and animal-like eukaryotes whose ranges can be resolved to one of 76 stage-long temporal intervals. Ranges are treated as continuous, and no information on sampling intensity is taken into consideration, with counts being either (A) totals of genera ranging into or across each bin or (B) totals of genera crossing the boundaries between each bin and the preceding bin. Upper curves (light shading) depict all marine taxa; lower curves (dark shading) depict core taxa analyzed in this paper (Anthozoa, Brachiopoda, Echinodermata, Mollusca, and Trilobita); legends and thick lines indicate this paper's two focal study intervals. formula image = Cambrian; O = Ordovician; S = Silurian; D = Devonian; C = Carboniferous; P = Permian; Tr = Triassic; J = Jurassic; K = Cretaceous; T = Tertiary.
Figure 2
Figure 2
Current marine paleofaunal contents of the Paleobiology Database. The curves show only the amount of raw data available for analysis and have no necessary biological meaning. Log scale is used because the variables are highly skewed on a linear scale. Period names are given in the legend for Fig. 1. Top black line, sum of squared counts of occurrences in each collection in each 10-Myr-long bin. Middle black line, number of taxonomic occurrences summed across collections in each bin. Bottom black line: number of fossil collections per bin in the two major study intervals. Thick gray line, number of distinct genera sampled in each bin. High diversity peaks in the late Ordovician and Maastrichtian correspond to relatively well-sampled temporal intervals; smaller-scale variation in this diversity curve also tracks variation in sampling intensity.
Figure 3
Figure 3
Diversity curves corrected for variation in sampling intensity by using four different subsampling algorithms (Table 2) and two methods of counting genera. Each data point represents the median value seen across 100 individual subsampling trials. Some data points are excluded when bins fail to meet the appropriate sampling quota. Filled circles show counts of genera actually sampled within a bin; open circles show counts of genera crossing the boundaries between consecutive bins. Legends labeled “95% CI” show the median 95% confidence interval across all intervals in a particular analysis; separate values for sampled-within-bin and boundary-crosser counts are illustrated. Only North American, European, North African, and Middle Eastern collections, and only occurrences of Anthozoa, Brachiopoda, Echinodermata, Mollusca, and Trilobita, are included in the analyses. Period names are given in the legend for Fig. 1. (A) Classical rarefaction of taxonomic occurrences. Individual taxonomic occurrences are randomly and independently drawn until each temporal bin includes 700 occurrences. (B) Subsampling by unweighted lists (UW). The algorithm draws 90 lists per bin. (C) Subsampling of lists weighted by taxonomic occurrences (OW). The number of taxonomic occurrences included in each list is summed, and lists are drawn until each bin includes lists totaling 700 occurrences. (D) Subsampling of lists weighted by taxonomic occurrences squared (O2W). This method counts the sum of the squared richness values for the lists that are drawn. Each bin includes 10,000 occurrences-squared.

Comment in

  • A new picture of life's history on Earth.
    Newman M. Newman M. Proc Natl Acad Sci U S A. 2001 May 22;98(11):5955-6. doi: 10.1073/pnas.121190498. Proc Natl Acad Sci U S A. 2001. PMID: 11371631 Free PMC article. No abstract available.

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