Research projects

Prof. Dr. Michael Hautmann

Effect of mass extinctions, biotic recoveries, and macroecological changes on taxonomic distinctness: A case study on bivalves during the Palaeozoic – Mesozoic transition

Leadership/contacts

Duration

September 2023 to August 2027

Funding sources

SNF, Personen- und Projektförderung

Regions

Summary

Analytical studies of biodiversity change through deep time have almost exclusively focused on richness, i.e. the number of taxa at a given level of the Linnaean taxonomy. Apart from prob-lems that result from the strong dependence of richness on sampling intensity and differences in the quality of the fossil record, this ‘taxic’ approach also ignores the amount of diversity that is pre-served deeper in the tree, beyond the taxonomic level at which richness is counted. This aspect has first been considered by conservation biologists, who have emphasized that a group of species in which each is the sole representative of a higher taxon preserves more disparity and evolutionary history than the same number of species that all belong to the same genus. Accordingly, a variety of techniques has been developed that measure the differences in the phylogenetic or taxonomic relatedness of species in an assemblage. Although these techniques have been applied successful-ly to the assessment of threatened communities, the characterization of certain environmental settings, and the monitoring of habitat degradation, they have never been used as tools in macro-evolutionary research. This project will analyse changes in the taxonomic relatedness of species in a major class of marine invertebrates during the greatest turnover in the history of marine life, using two main parameters: (i) average taxonomic distinctness (AvTD), which is the average taxonomic path length between any two randomly chosen species, and (ii) variation of taxonomic distinctness (VarTD), which is the variance of these pairwise path lengths. These parameters capture the ne-glected aspect of changes in the taxonomic structure in response to a changing macroecological background and have the analytical benefit of a virtual independence from sampling effort. Based on a coherent taxonomic concept, AvTD and VarTD will be calculated for bivalve faunas from the Permian to the Jurassic, which encompasses two major mass extinctions and ensuing recoveries, the shift from the Palaeozoic evolutionary fauna to the Modern evolutionary fauna, and the initial Mesozoic marine revolution. Key questions addressed in this research include (i) the role of mass extinctions in the elimination of evolutionary history, as preserved in the taxonomic structure, (ii) the question whether the excess of ecological opportunities after mass extinctions manifests pre-dominantly in the lower or higher levels of the taxonomic tree, corresponding to either a richness-first or a disparity-first mode of evolution, and (iii) the effect of changing levels of biotic interactions on the taxonomic structure, exemplified by increased intensity of predation during the Mesozoic marine revolution. The results will be compared with those of traditional richness analyses in order to assess the benefit of taxonomic distinctness studies as a complementary approach.