UC San Diego

The relative importance of biotic interactions relative to environmental forcing is a fundamental question in paleontology and evolutionary biology. Predictive models generally focus on forcing entirely derived from either one or the other of these two possible mechanisms. Testing the relative effects of these drivers is difficult, and to date has not been carried out in a rigorous quantitative setting in which ecology and environment can both be independently determined. The work presented here uses the family Pectinidae, the scallops, from either side of the Isthmus of Panama, extending back 12 Ma to address this question. Evolutionary patterns of diversity, extinction and origination in scallops are similar to those observed in bivalves as a whole, including a high level extinction 1 to 2 Myr after the final closing of the Isthmus of Panama. However, evolutionary patterns varied considerably among different ecological groups. Larval ecology of scallops evolved in response to changing environments in the Caribbean in a manner predicted by ecological models. Body size evolved in a manner predicted by competitive interactions but was also highly constrained by life habit and life history of the taxa. The overall evolutionary pattern of tropical American scallops was consistent with the model of extinction derived from metapopulation theory that help to explain the significant time delay in extinction patterns relative to environmental changes within newly forming habitats in the Caribbean. Taken together, these results indicate that both biotic interactions and environmental forcing had significant effects on evolutionary patterns. Biotic effects were constrained within limits set by life history and life habit, which evolved in response to the environment. Finally, the success of applying metapopulation models and ecologically based models of larval ecology indicates that scaling ecological models upwards provides much better explanations of evolutionary patterns than predictions based on intrinsic macroevolutionary characteristics