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Older species: a rejuvenation on coral reefs?

Authors


John C. Briggs, 82-651 Skyview Lane, Indio, CA 92201, USA.
E-mail: johnc.briggs@verizon.net

Abstract

Aim  To discuss the theory that the present high species diversity and apomorphic character of the coral reef ecosystem is because of the historic accumulation of basal species from marginal habitats.

Location  The Indo-West Pacific Ocean.

Methods  The examination of biogeographical patterns from the standpoint of paleontology, phylogeny, genetics, and empirical data.

Results  Fossil patterns from several clades indicate a gradient of increasing average generic age that extends outward from the high diversity reefs. Successful species that give rise to new species, genera, and families apparently originate from high diversity locations. The tropics have been a major source of evolutionary novelty, not simply a refuge that has accumulated diversity. Many plesiomorphic clades, that once dominated the shallow tropics, are now limited to the deep sea and other safe places. Recent research on several tropical fish families indicates that more apomorphic species inhabit the high diversity reefs. Genetic studies suggest that a decrease in genetic variation extends from the diversity centre toward the outer reaches of the Indo-West Pacific. Empirical data show that it is extremely difficult for species from low diversity areas to invade places of higher diversity.

Main conclusions  There is no convincing evidence to indicate that basal species from marginal habitats have been able to accumulate on the coral reefs. Once such species have been displaced from a high diversity environment, there is apparently no return. The evolutionary innovations that contribute to the origination of new phyletic lines take place under conditions of high diversity and maximum competition.

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