PLANKTIC FORAMINIFERAL DIVERSITY: LOGISTIC GROWTH COMPLICATED BY A VARIABLE ENVIRONMENT

Deciphering the factors underlying both long-term patterns of diversity and taxonomic turnover rates (i.e., extinction, and origination) has been one of paleobiology’s major foci for the past three decades. The importance of documenting these components is that they will expand our ability to interpret and model the evolutionary processes underlying those trends, highlight the evolutionary impact of historical events, and contribute to the formulation of robust predictions about the future of global diversity in response to the current anthropogenically driven environmental changes. Here, we have scrutinized the possible primary causes on planktic foraminiferal long-term diversity dynamics by determining quantitative relationships between their global fossil diversity pattern (~170 Ma to present) at the morphospecies level with coeval mean global marine geochemical and geological signatures which serve as established environmental proxies. Furthermore, we inferred interspecific competition levels in the group through time based on significant cross-correlations displayed between planktic foraminiferal extinction and origination rates. Results obtained from these analyses suggest that changes in vertical stratification on the oceanic upper mixed layer, led by temperature variation, represent an important control on global planktic foraminiferal standing diversity levels through the Meso- and Cenozoic. Moreover, the combination of significant relationships between the global planktic foraminiferal diversity pattern with both global mean oceanic temperature and interspecific planktic foraminiferal competition suggests that throughout the long-term, species richness has changed in lockstep with the vertical range of the pelagic upper-mixed layer. This dynamic likely influenced the availability of niche space, as a consequence of strong interspecific competition, which has allowed the group to track the fluctuating carrying capacity of the system (forced by the global oceanic temperature changes) resulting in a ‘complex’ logistic diversification pattern.