“Species-level diversity and the underlying mechanisms that lead to the formation of new species, that is, speciation, have often been confounded with intraspecific diversity and population subdivision. The delineation between intraspecific and interspecific divergence processes has received much less attention than species delimitation.” (Jen-Pan Huang, 2020, p. 6890)
(Chrono-) Species are defined by age, with 2 Ma being considered a reasonable temporal threshold value. Consequently, speciation is defined as a splitting event that brings up taxa that are at least 2 Ma old. More recent splittings will have to be treated as subspeciations and infrasubspeciations, respectively. The threshold value for the former is defined as 1 Ma, and for the latter as 0,5 Ma.
Explicit timetrees (i.e. dated phylogenies with divergence times being explicitly specified) can provide information on time-intervals that separate successive splittings. Analysing “interdivergence times” is meaningful only in clades exhibiting extraordinary radiation. In birds, Telluraves and Sylviida offer the opportunity for such evaluation. The resulting data indicate that successive splittings can occur within 0,5-1 million years, but usually take 1-1,5 million years. Cladogenesis thus can comprise speciation, subspeciation, and infrasubspeciation.
Radiations with short interdivergence times (in million years, Ma). Green boxes indicate times
between 1-1,5 Ma, red boxes times less than 1 Ma.
Campbell CR, Poelstra JW, and Yoder AD (2018), What is speciation genomics? The roles of ecology, gene flow, and genomic architecture in the formation of species, Biol. J. Linn. Soc. 124, 561–583. (free pdf)
Huang JP (2020) Is population subdivision different from speciation?, Ecol. Evol. 10, 6890-96. (pdf)
Vaux F, Trewick SA, and Morgan-Richards M (2016), Lineages, splits and divergence challenge whether the terms anagenesis and cladogenesis are necessary, Biol. J. Linn. Soc. 117, 165-176. (pdf)