TURNOVER-PULSES, THE RED QUEEN, AND RELATED TOPICS

The turnover-pulse hypothesis is discussed more fully than previously (Vrba, 1985), and compared to the Red Queen's hypothesis and the prediction of constant extinction (Van Valen, 1973), and to the modified Red Queen's hypothesis with outcomes of either steady or stationary states (Stenseth and Maynard Smith, 1084). The turnover-pulse hypothesis postulates (1) that conspecific organisms interact with both physical and biotic components of the species-specific habitat that may extend across differing ecosystems, and (2) that physical change is the initiator of biotic changes and of pulses of species turnover. Under the two Red Queen models, interactions among organisms of different species present in each particular ecosystem drive evolution, speciation, and extinction. Th logical connection between Red Queen ecosystemic processes and predictions of speciations and extinctions has not been consistently argued. One problem arises because single species commonly occur across different ecosystems such that their populations have different ecological histories, and most changes in species composition in ecosystems do not correspond to changes in genealogical species turnover. A second problem concerns how speciation and extinction are defined relative to phylogeny: For instance, Van Valen's Red Queen model implies phylogenies that include substantial ''pseudo-speciation'' and ''pseudo-extinction,'' subsumed by him under speciation and extinction respectively. To the extent that such pseudo-events are present, the proposal that Red Queen evolution predicts constant extinction, namely that ''rate of species extinction is independent of species duration,'' does not make sense. Constant extinction in the survivorship sense can result from evolution under several other models.