Stasis and Change Reconsidered

Potts (1984) proposed an individualistic explanation for faunal stasis after the Plio-Pleistocene turnover. For Indo-Pacific corals with long generation times, continual disturbance in the Plio-Pleistocene maintained high intraspecific genetic variation. The result was low turnover of the coral fauna (see also Veron 1985,1995). A similar individualistic hypothesis can be constructed for the Caribbean fauna, although there are some species with short generation times to which the model apparently does not apply (Potts and Garthwaite

1991). Jackson and Budd (1996) suggested as an alternative that Pleistocene stasis occurred in the Caribbean because those species that passed through the Plio-Pleistocene filter were eurytopic: Their preadaptations made them resistant to subsequent fluctuations.

The two explanations are really quite similar. In each hypothesis, the mechanisms maintaining stasis before and after the turnover event were different. Before the turnover, a long period of stasis occurred in a relatively benign environment. That stasis was shattered by environmental change during the Plio-Pleistocene. Then, after the turnover, stasis occurred despite continued environmental change because of the eurytopic (Jackson and Budd 1996) or plastic and variable (Potts 1984) nature of the coral species. Most recently, new combinations of coral diseases and other factors have overwhelmed the capacity of the eurytopic or plastic species to adjust to new conditions, hence the sudden biotic shift of the last 20 years. Ecological and evolutionary stasis and change of the Caribbean coral fauna thus becomes largely an observation of species' independent responses to the tempo and amplitude of environmental change.

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