ARE GENERA AND 10 MY BINNED DATA ADEQUATE FOR STUDIES OF DIVERSITY AND ENVIRONMENTAL CHANGE?

Paleodiversity studies, e.g. those done using the PBDB, typically use genera as proxies for species, and time bins of several (often ca 10) my. These studies often claim [at least in the proposal request] to be relevant to understanding the effects of future environment change on living diversity. Few studies have tested the effects of genus data, or coarse bin sizes on diversity results, nor has the effect of these on correlations to environmental change been adequately examined. Such tests can best be made using data that conventional studies lack: where species are resolved, time bins are 1 my or less, and environmental data is directly correlatable to diversity data. We have examined the effects of using genera and coarse time bins on paleodiversity estimates and correlations to environmental change using the marine microfossil record of diatom species diversity and marine stable isotope records. This was recently studied using the NSB database of marine microfossil species occurrences, with 0.5-1 my time bins (Lazarus et al. 2014, PlosOne). This paper noted a highly significant correlation of diatom species diversity to environmental change, particularly in the Neogene, and suggested that future global warming might risk substantial extinctions of global carbon budget significant cold-adapted diatom species. We re-analysed this data, using genera instead of species, and time bins of 5 my or substage length. None of the primary conclusions of this paper were seen in the genus level data. Genus diversity is nearly flat from the Oligocene-Recent, unlike the published species results, where species diversity and environmental parameters covary significantly over the same time interval. Long time bins also substantially degraded the recovered signal, though to a lesser degree than the use of genera.

We suggest that, particularly for studies of paleodiversity and environmental change, more effort be made to use species data, or at least to verify from modern (geographic) studies that genera are adequate proxies for species and their correlation to environment.