Speciation-by-Extinction.

The article focuses on the model of "speciation-by-extinction," wherein speciation occurs through the extinction of intermediate populations within a geographically variable species, resulting in discontinuities in heritable traits sufficient to define distinct species. This model contrasts with the classic "isolation-then-divergence" speciation framework by proposing that no further divergence after extinction is necessary for speciation to be complete. Empirical evidence from experimental extinction scenarios in species such as the Andean songbird Cranioleuca antisiensis and the plethodontid salamander Ensatina eschscholtzii supports the plausibility of speciation-by-extinction. The authors argue that because geographically structured intraspecific variation and local extinction are common in nature, speciation-by-extinction may be a widespread but underrecognized mechanism, and they encourage further research to distinguish it from other speciation processes using empirical data.