The role of temporal abundance structure and habitat preferences in the survival of conodonts during the mid-early Silurian Ireviken mass extinction event.

Andrej Spiridonov,Sigitas Radzevičius,Antanas Brazauskas,Steffen Kiel

doi:10.1371/journal.pone.0124146

Abstract

The Ireviken event was one of the most intense extinction episodes that occurred during the mid-Paleozoic era. It had a strong global effect on a range of clades, with conodonts, graptolites and chitinozoans affected most. Using geophysical proxies and conodont species parameters of their temporal abundance structure we investigate how they affected the selectivity of conodont species survival during this calamity. After performing bivariate logistic analyses on 34 species of conodonts, we find three variables that were statistically significantly associated with their odds of survival. These namely include spectral exponents that describe degrees of autocorrelation in a time series, the skewness of species abundance distribution, and average environmental preferences, which are mostly determined by ancient water depths at sampling sites. Model selection of multivariate logistic models found the best model includes species local abundance skewness and substrate preference. A similar pattern is revealed through the regression tree analysis. The apparent extinction selectivity points to a possible causes of environmental deterioration during the Ireviken event. The significant positive relationship between extinction risk and preferential existence in deeper environments suggests the open ocean causal mechanisms of biotic stress that occurred during the Ireviken event. Marine regressions, which were previously suggested as a causal factor in this extinction episode, on theoretical grounds should have had higher impact on species living in near-shore environments, through the processes of habitat loss which are associated with decreases of shelfal areas. In addition, the significant positive correlations found between skewness of abundance distributions and spectral exponent values and the probability of species survival suggest that community and ecosystem processes (which controlled species abundance fluctuation patterns) were significantly related to selectivity processes of this smaller mass extinction event.

Highlights

This study focuses on the Ireviken event, which is known as the mid-early Silurian event
It was found that larger species abundance distribution skewness and smaller rock gamma-ray values in rocks in which species were found correlate with a higher probability of conodont species survival during the Ireviken event
The bivariate logistic regression analyses revealed that important factors of conodont species survival during the mid-early Silurian Ireviken extinction event include abundance distribution skewness (G(a)), the spectral exponents of abundance time series (ν), and environmental preference patterns as reflected by average gamma radiation intensities in the sampling sites

Summary

Introduction

This study focuses on the Ireviken event, which is known as the mid-early Silurian event. Since this study was published, this event has been thoroughly researched by conodont workers based in other localities of the Baltica and in other paleocontinents and terrain regions [3,5,6,7] These additional studies supported the step-like pattern with two to three more turnover events [6]. Microplankton, according to material from Gotland, were affected to a lesser extent, with 18% of species (12 out of 72) eliminated due to extinction and extirpation [14] and similar patterns have been observed for the brachiopods [15] Ireviken perturbation in the former group more closely resembled a turnover pulse (sensu [16]) macroevolutionary event than a true mass extinction event, as the event produced a net increase in palynomorph diversity [14]

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Results

Discussion

Conclusion