GLOBAL PHANEROZOIC BIODIVERSITY – CAN VARIATION BE EXPLAINED BY SPATIAL SAMPLING INTENSITY?

Variation in observed global generic richness over the Phanerozoic must be explained in part by changes in the number of fossils and their geographic spread over time. The influence of sampling intensity (i.e., the number of samples) has been well addressed, but the extent to which the geographic distribution of samples might influence biodiversity is comparatively unknown. To investigate this question, we create steady state models of genus richness through time by resampling occurrence datasets of Modern global biodiversity using spatially explicit sampling intensity defined by the paleo-coordinates of occurrences from the Paleobiology Database (PBDB). Fossil occurrences are parsed into ~11 myr time bins and spatially grouped into 812 equal-area grid cells. For each time slice, the number of taxa and occurrences are recorded for each cell, along with the cell’s latitudinal and longitudinal coordinates. Then, modern grid cells are selected to match the geographic distribution of fossil cells such that the number of sampled cells in a band of latitude is equal for both the modern and fossil data. Three separate sets of Modern data, sourced from the Ocean Biodiversity Information Service (OBIS), eBird Observation Dataset (EOD) and Global Biodiversity Information Facility (GBIF), and several fully synthetic datasets are explored. Occurrences are randomly drawn from the selected modern cells such that the total number of occurrences and their distribution among cells is identical to the fossil record sampling, and the total number of unique genera found (predicted genus richness) is recorded. 25 replicates are performed for each time bin, and the procedure is repeated for each of 48 paleo time bins spanning the Phanerozoic. Using linear regression analysis, we then compare richness estimates over time derived from the PBDB to predictions of the steady state models, which sample only the modern but with PBDB-dictated spatial coverage. While our intent was to reject the null hypothesis that richness has not changed through time, preliminary results suggest that the steady state models cannot be rejected. Possible implications arising include 1) fossil richness estimates are flawed when spatial sampling is limited, or 2) marine invertebrate diversity has not significantly changed through time.