Diversity trends within a model taxonomic hierarchy

Abstract

Most processes of diversification and extinction operate at the level of species, yet the fossil record of species is so poor that long-term species diversity trends cannot be recovered. Instead, higher taxonomic levels, usually families, are studied, and a kinetics of diversity had been proposed for some higher levels. A computer simulation of the behavior of diversity at four levels within a model of a taxonomic hierarchy is used to attempt to understand the relation of species-level to family-level diversity. Under conditions which approximate those found in nature, including episodic small extinction peaks and occasional mass extinctions, species diversity is volatile and the ratio of species to higher-level taxa is highly variable. Plateaus in diversity of higher taxa do not reflect constant species diversities and such taxa should not be modeled as equilibrium systems, although they are useful in interpreting ancient biosphere conditions; the Paleozoic marine family plateau certainly suggests that biosphere structure remained broadly similar and that no marked reorganization of the marine fauna occurred for around 200 million years.