Diversity-dependent evolutionary rates in early Palaeozoic zooplankton

Area of Science:

• Paleontology
• Macroevolutionary Dynamics
• Marine Biology

Background:

• Understanding macroevolutionary dynamics hinges on the relationship between biological diversity and diversification rates.
• The role of diversity-dependence in evolutionary rates remains a key debate in macroevolutionary studies.
• Early Palaeozoic marine zooplankton, like graptoloids, offer a high-resolution fossil record to investigate these dynamics.

Purpose of the Study:

• To test whether diversification rates in early Palaeozoic graptoloids were influenced by standing diversity levels.
• To address the statistical artifact of regression-to-the-mean in diversity-rate analyses.
• To quantify the impact of diversity-dependence on macroevolutionary rates.

Main Methods:

• Analysis of a high-resolution, species-level fossil record of early Palaeozoic graptoloids.
• Construction of a non-parametric, empirically scaled, diversity-independent null model by randomizing diversification rates over time.
• Comparison of observed diversity-diversification rate correlations against the null model.

Main Results:

• Evidence for significant negative diversity-dependence in graptoloid diversification rates was found.
• This negative diversity-dependence accounted for up to 12% of the variance in diversification rate.
• The strongest correlation between diversity and diversification rate occurred with a temporal lag of approximately 1 million years.
• Diversity-dependence persisted through the Ordovician and Silurian, despite increased extinction and speciation pulses in the Silurian.
• Speciation and extinction rates were affected nearly equally by diversity-dependence on average.

Conclusions:

• Biological diversity plays a significant role in regulating macroevolutionary rates, specifically exhibiting negative diversity-dependence in early Palaeozoic marine zooplankton.
• The findings provide empirical support for diversity-dependence as a key factor in macroevolutionary dynamics, influencing both speciation and extinction.
• Diversity-dependence is a persistent feature of evolutionary dynamics, even amidst major environmental or ecological shifts like those seen in the Silurian.