Taxon cycles refer to a biogeographical theory of how species evolve through

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

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 Edward Osborne Wilson (June 10, 1929 – December 26, 2021) was an American biologist, naturalist, ecologist, and entomologist known for developing the field of sociobiology. Born in Alabama, Wilson found an early interest in nature and frequ ...

in 1961 after he surveyed the distributions,

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

s, behavior and morphology of

ant Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Cre ...

species in the

Melanesia Melanesia (, ) is a subregion of Oceania in the southwestern Pacific Ocean. It extends from New Guinea in the west to the Fiji Islands in the east, and includes the Arafura Sea. The region includes the four independent countries of Fiji, Vanu ...

n archipelago.

Stages of the taxon cycle

Wilson categorized species into evolutionary "stages", which today are commonly described in the outline by Ricklefs & Cox (1972). 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 and combined with concepts from

ecological succession Ecological succession is the process of how species compositions change in an Community (ecology), ecological community over time. The two main categories of ecological succession are primary succession and secondary succession. Primary successi ...

and

speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

cycle theories. Taxon cycles have mainly been described in island settings (archipelagos), where the distributions and movements of species are readily recognized, but may also occur in continental biota. * Stage I: Young, rapidly expanding, undifferentiated, widely and continuously distributed species in the initial

colonization 475px, Map of the year each country achieved List of sovereign states by date of formation, independence. Colonization (British English: colonisation) is a process of establishing occupation of or control over foreign territories or peoples f ...

stage inhabiting small island, coastal or disturbed (marginal) habitat. Such species are hypothesized to include very good dispersers,

ephemeral Ephemerality (from the Greek word , meaning 'lasting only one day') is the concept of things being transitory, existing only briefly. Academically, the term ephemeral constitutionally describes a diverse assortment of things and experiences, fr ...

species and ecological "

supertramp Supertramp were a British rock band formed in London in 1970. Marked by the individual songwriting of founders Roger Hodgson (vocals, keyboards and guitars) and Rick Davies (vocals and keyboards), the group were distinguished for blending p ...

s". * Stage II: Species that are generally widespread across many islands, but where geographical expansion has slowed, population differentiation has generated

subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...

or incipient species, and local extinction on small islands may have created gaps in the distribution. This stage includes species that have maintained a relatively good dispersal ability such as " great speciators". Early-stage "

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

es" may consist of stage II species. * Stage III: Older, well-differentiated and well-defined

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

that have moved to habitats inland (and uphill) and where reduced dispersal ability and extinctions have fragmented the distribution to fewer and larger islands. These species may be niche specialists, but novel adaptations or accidental dispersal may restart the taxon cycle. * Stage IV: Old, relictual,

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

species in the "final" stage are restricted to island interiors (mountains) on a few, large islands. This stage includes sedentary high‐elevation specialists with limited dispersal abilities and small range sizes. These species are evolutionary distinctive, as closely related species (and subspecies) have gone extinct.
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. Ricklefs & Bermingham (2002) estimated that taxon cycles take place over periods of 0.1-10 million years in different bird groups of the

Lesser Antilles The Lesser Antilles is a group of islands in the Caribbean Sea, forming part of the West Indies in Caribbean, Caribbean region of the Americas. They are distinguished from the larger islands of the Greater Antilles to the west. They form an arc w ...

islands. Pepke et al. (2019) 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 The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

bird family.

References

{{reflist Biogeography