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Is there a limit to global biodiversity in our oceans? This controversial question has sparked debate in evolutionary ecology for decades. Previous studies have mostly relied on global fossil diversity curves to shed light on this question, but this method has numerous limitations, as it does not account for considerable variable diversity among geographical regions or for fossil record biases. In this study, authors coupled regional logistic and exponential models of diversification to a global model of palaeogeography and plate-motion, to reconstruct global diversity dynamics during the Phanerozoic. These complex and inclusive methods contain evolutionary time-within-regions.
The palaeogeographical model used herein, merges existing models from previous works that published global reconstruction datasets (see publication references). These palaeogeographical reconstructions were used to describe and present the Earth’s palaeotopography and palaeobathymetry for a series of time slices from 541 million years ago to the present day (figure). The diversification models included imposing mass extinctions extracted from fossil diversity curves generated by previous works. Palaeoenvironmental conditions of seawater temperature and organic carbon export production were simulated using the Earth system model, cGENIE41, for the same timeframe as the Palaeogeographical model reconstructions.
The two regional diversification models of diversification were used to describe the dynamics of regional diversity over time. The regional diversity was interpolated into the palaeogeographical model grids to calculate global diversity at each time step. The resulting reconstructions of Phanerozoic oceans (figure), present the spatial distribution sequences of marine animal diversity, as number of genera per area, for each of the six time periods (from a - f): Cambrian, Late Ordovician, Early Devonian, Late Carboniferous , Late Cretaceous and the present day, respectively.
The performance of the model in reconstructing spatial distributions of marine invertebrate diversity was evaluated by comparing the results of the present-day calibrated logistic model (thus 0 million years ago), with observations of crustaceans and molluscs (two of the most relevant groups of marine invertebrates), extracted from the Ocean Biodiversity Information System (OBIS). The model generated diversity map shows notable similarities to the observed diversity distributions (occurrence records) from OBIS, along the continental margins (figure g-h). The main differences between the model generated diversity and occurrence records from OBIS, occur in the regions surrounding Australia and New Zealand, where the model underestimates diversity. A possible reason for the slight discrepancies between the model and OBIS data, may be due to database limitations. What both the applied model and OBIS data similarly depict, is a diversity decline from the equator towards the North- and South poles (figure i-j), with high diversity in the Indo-West Pacific, the Atlantic Caribbean-East Pacific and the Mediterranean.
The results of the diversification models further reveal that the diversity of marine invertebrates has remained below ecological saturation throughout their evolutionary history, with the possible exception of diversity hotspots. Authors found that their generated model can reproduce an increase in diversity without evolutionary innovations (such as the Mesozoic marine revolution), leading to a newly proposed hypothesis, the ‘diversity hotspots hypothesis’, which is based on how the environmental history and palaeogeographical evolution of the Earth enabled the development of diversity hotspots.
Cermeño P, García-Comas C, Pohl A, Williams S, Benton MJ, Chaudhary C, Le Gland G, Müller RD, Ridgwell A, Vallina SM. 2022. Post-extinction recovery of the Phanerozoic oceans and biodiversity hotspots. Nature. doi: 10.1038/s41586-022-04932-6.