Adaptive radiation

Adaptive radiation is rapid evolutionary radiation. It is an increase in the number and diversity of species in each lineage. It produces more new species, and those species live in a wider range of habitats.^[1]

Some definitions phrase it in terms of a single clade: "Adaptive radiation is the rapid proliferation of new taxa from a single ancestral group".^[2] However, in the most striking cases, such as occurred in the Triassic after the greatest extinction event in Earth history,^[3] many lines underwent rapid radiation simultaneously. This must have something to do with the availability of ecological niches and relative little competition.

The Ediacaran biota were the result of an early metazoan radiation. The greatest radiation of all took place early in the Cambrian period, when most of our animal phyla evolved: see List of animal phyla.

With less competition, groups diversify to fill available habitats and niches.^[1] This is an evolutionary process driven by natural selection.^[4]

The term was introduced and discussed by George Gaylord Simpson, the palaeontologist who contributed to the modern evolutionary synthesis.^[5][6] Others prefer not to use the term. Robert L Carroll prefers to use the term major evolutionary transitions, though it turns out that all or most of these could also be described as adaptive radiations.^[7] Others use terms like macroevolution, or even megaevolution, as if the processes are different from those which occur below species level. It is part of evolutionary theory that all processes take place at the level of populations. All agree, though, that the speed of evolution does change, however it is measured.

1. ↑ ^{1.0 1.1} Schluter D. 2000. The ecology of adaptive radiation. Oxford University Press.
2. ↑ Stanley S.M. 1979. Macroevolution: pattern and process. Freeman, S.F. p65
3. ↑ The P/Tr extinction event
4. ↑ Mayer, Ernst. 2001. What evolution is. Basic Books, New York, NY.
5. ↑ Simpson G.G. 1944. Tempo and mode in evolution. Columbia, N.Y.
6. ↑ Simpson G.G. 1953. The major features of evolution. Columbia, N.Y.
7. ↑ Carroll, Robert L. 1997. Patterns and processes of vertebrate evolution. Cambridge.