Ecological controls of marine biodiversity dynamics on large temporal scales: the Triassic-Jurassic example
By Wolfgang Kiessling.
The Paleobiology database (PBDB) makes is possible to assess rigorously the relationship between evolutionary rates and ecological traits. I use a large and taxonomically vetted dataset on Triassic-Jurassic benthic marine organisms from this database to explore the dependencies of biodiversity dynamics from (1) abundance and geographic distribution and (2) environmental affinities of genera. Abundance and geographic distribution were estimated by occurrence counts and great circle distances on palaeogeographic reconstructions, respectively. Environmental affinities were assigned by calculating binomial probabilities of proportional occurrence counts and separated affinities for: (a) carbonate vs. siliciclastic substrates, (b) onshore vs. offshore depositional environments, (c) reefs vs. level-bottom communities, and (d) tropical vs. non-tropical latitudinal zones. A sampling-standardized analysis of diversity dynamics yielded: (1) Both abundance and geographic range are very good predictors of extinction risk but also of origination probability. Rare and geographically restricted genera tend to show much higher turnover rates and lower longevities than common and widely distributed taxa. (2) Environmental affinities of taxa are also significantly tied to turnover rates but not to longevities, because there are higher probabilities of origination but not of extinction for taxa dwelling on carbonate substrates, onshore and in reefs than for taxa preferring clastic substrates, offshore settings and level-bottom communities. The absence of significant differences between the biodiversity dynamics of tropical and non-tropical taxa calls into question that the tropics are universally cradles and/or museums of evolution. The investigated time series includes one of the Big Five mass extinctions of the Phanerozoic. This extinction exhibits interesting deviations from the background pattern: Neither abundance nor geographic distribution did form an insurance against extinction but there is a significant extinction peak for tropical taxa. Therefore, short-term climatic change (most probably a warming pulse due to volcanic outgassing) appears to have played a substantial role in the mass extinction.
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