HOW TO TEST MACROEVOLUTIONARY PROCESS HYPOTHESES: PALEOBIOGEOGRAPHIC SELECTIVITY AT THE END-ORDOVICIAN MASS EXTINCTION EVENT

Are cosmopolitan species more likely than provincial species to survive apparently global mass-extinction events? This effect, claimed as an empirical cornerstone of macroevolution and species selection, presumably would arise through effective geographic stochasticity -- so that the broader a species’ biogeographic range, the more likely that species is to be represented in geographic regions less hard-hit by the event (i.e., “refugia”). However, if the more cogent factor enhancing survivorship is not range per se but rather representation in those particular "refugia" (e.g., Australia), then the target of selection is no longer a trait at the species level (e.g., inhabiting Australia is a trait of individuals). In such a case, it is selection on individuals, not on species, that is responsible for the macroscale evolutionary patterns.

Multiple-regression analysis reveals that for rhynchonellide brachiopods at the end-Ordovician mass-extinction event, survivorship is better predicted by representation in particular “refugia” than by paleobiogeographic breadth. Furthermore, paleobiogeographic breadth data add no significant predictive information to the correlational relationship between survivorship and refugial representation, while refugial representation data do contribute such significant predictive information. If biogeographic range was a predictive factor at the end-Ordovician mass-extinction event, it was not via macroevolutionary stochasticity, but rather via historically determinate paleobiogeographic "refugia." The true role of species-selection and other “macroevolutionary processes” will become clear only when we begin testing their predictions against their counterparts at the individual level of Darwinian process.