Speciation completion rates have limited impact on macroevolutionary diversification.

Area of Science:

• Macroevolutionary biology
• Phylogenetic modeling
• Theoretical ecology

Background:

• Standard birth-death (BD) models assume instantaneous speciation, limiting interpretations of macroevolutionary rates.
• The protracted birth-death (PBD) model offers a more realistic two-step speciation process (initiation and completion).

Purpose of the Study:

• To compute an equivalent time-varying BD scenario to the PBD model.
• To understand the influence of speciation initiation and completion on macroevolutionary rates.
• To establish a theoretical framework linking microevolutionary processes to macroevolutionary diversification.

Main Methods:

• Developed an 'equivalent' standard time-varying birth-death (BD) scenario for comparison with the protracted birth-death (PBD) model.
• Analyzed speciation and extinction probabilities within this framework.
• Computed equivalent birth rates under different model parameters.

Main Results:

• Identified a sharp decline in the equivalent birth rate near the present, suggesting tip-based rate estimates may be inaccurate.
• Determined that speciation completion rate influences the timing of rate decay, not asymptotic rates.
• Found that past equivalent birth rates scale with speciation initiation rates, modulated by population extinction rates.

Conclusions:

• Population formation and extinction rates are crucial drivers of speciation, potentially more so than reproductive isolation speed.
• The PBD model provides a more nuanced understanding of macroevolutionary diversification.
• Microevolutionary processes significantly shape species diversification over macroevolutionary timescales.