Taxon cycles refer to a biogeographical theory of how species evolve through range expansions and contractions over time associated with adaptive shifts in the ecology and morphology of species. The taxon cycle concept was explicitly formulated by biologist E. O. Wilson in 1961 [1] after he surveyed the distributions, habitats, behavior and morphology of ant species in the Melanesian archipelago. [2]
Wilson categorized species into evolutionary "stages", which today are commonly described in the outline by Ricklefs & Cox (1972). [3] However, with the advent of molecular techniques to construct time-calibrated phylogenetic relationships between species, the taxon cycle concept was further developed to include well-defined temporal scales [4] and combined with concepts from ecological succession and speciation cycle theories. [5] Taxon cycles have mainly been described in island settings (archipelagos), where the distributions and movements of species are readily recognized, [6] but may also occur in continental biota.
The ecology and evolution of the Melanesian ants that originally inspired Wilson's hypothesis have since been shown to be consistent with the taxon cycle predictions using modern methods. [8] Ricklefs & Bermingham (2002) [6] estimated that taxon cycles take place over periods of 0.1-10 million years in different bird groups of the Lesser Antilles islands. Pepke et al. (2019) [5] used the difference in mean age of late- and early-stage species as a lower estimate (4.7 million years) of the tempo of taxon cycling in an Indo-Pacific bird family.