Table 1.
Functional axes used in this study.
Table 2.
Origination rates for bivalve functional groups.
Figure 1.
Global patterns in Functional richness (FR) and Functional evenness (FEve) for marine bivalves.
Heatmaps are interpolated from data for 10° latitudinal bands for (A) FR and (B) FEve. (C) Raw observations are plotted against latitude, showing the LDG in taxonomic richness (top, gray squares and black line), functional richness (top, black circles and gray line), and functional evenness (bottom). For both plots, the region in pale gray represents the central 95% of FRs or FEves from 1000 random draws for each latitude/coast combination. Observed FR and FEve are both broadly consistent with the null expectations given the taxonomic richness of each bin, and thus consistent with the high-latitude fauna being an attenuated sample of the global genus pool.
Figure 2.
Origination rates for bivalve functional groups.
Origination rates (genera · my−1) vary among bivalve functional groups. As a result, groups with higher origination rates represent a larger proportion of the overall fauna, contributing to the inherent unevenness in the bivalve gene pool (A, each point represents a distinct functional group, see Table 2). When coupled with an “Out of the Tropics” dynamic, FEve and the standard error in genus age both correlate strongly with latitude, and with each other (B). Each point represents a single 10° band on a given coastline; regressions were calculated for all coastlines pooled together. Origination rates are based on geological age-frequency distributions of extant genera in the form of “backwards survivorship curves” [33], [34].
Figure 3.
Random sampling of even and uneven taxon pools.
FEve is calculated from branch lengths of the minimum spanning tree (MST) connecting all taxa in a functional ordination [15]. When a taxon pool with low FEve is randomly sampled, the samples have higher FEve, as illustrated here. Panels A and B are PCoA plots with MSTs superimposed. For both panels, the left-most plot shows a taxon pool while the three right-most plots show three random samples from that pool. Panel A shows a randomly generated dataset, having the same dimensions as the bivalve genus data — a very even taxon pool. Randomly sampling from an even pool does not alter the evenness. Panel B shows data for all bivalve genera — an uneven taxon pool. Randomly sampling from an uneven taxon pool causes FEve to increase. (The pattern holds for 1000 random samples, as shown in Figure 1C). Panel C shows the distribution of MST branch lengths for each of the 8 plots in panels A-B. Despite the highly skewed distribution of branch lengths for the pool of all genera, samples from that pool have a relatively more even distribution of branch lengths than seen in the entire pool.