IMPLICATIONS OF A NEW HIERARCHICAL BRANCHING MODEL FOR LEVELS OF SELECTION AND THE LAW OF CONSTANT EXTINCTION

The effect of species selection on the shape of taxonomic survivorship curves is unknown. Traditionally, in the study of species selection, identification of selection occurring between species is the goal. In this study, the focus is on the interactions between two hierarchical levels of selection occurring at different taxonomic of evolutionary levels, the generic and the specific (e.g. species with in genera, genera with in families, or organisms with in species). I model this situation with a new four parameter hierarchical branching model. Origination and extinction rates for both levels interact to generate diversity dynamics and taxonomic survivorship patterns. Varying these rates, and therefore changing the characteristic time scale for each level, determines which level predominates. With this model it is possible to define the domain of rates where a generic level process is effectively reducible to the specific level. In this domain, the probability of generic extinction is age dependent. In the compliment of this domain the Law of Constant Extinction applies. Empirical predictions for the shape of taxonomic survivorship curves at different hierarchical levels are provided for the cases of two levels of selection and simple scaling of origination and extinction up the taxonomic hierarchy, with selection occurring only at the lower level.