The diversity of life comprises clades that are rich and poor, old and young, uniform and varied. Biodiversity, therefore, seems to conform only to the organizational laws of microevolution. So what general principles, if any, constrain the evolution of biodiversity across macroevolutionary time? We apply time-variable, environment-dependent models of diversification and non-parametric maps of phylogenetic space to family-level trees spanning 12k vertebrate species and a diatom phylogeny constructed from 214k V9-18S ribotypes, in order to characterize the evolution of biodiversity in vertebrates and diatoms from the Cretaceous to the present.
Results/Conclusions
We present a general model for investigating how biodiversity evolves in deep time. In vertebrates, we show that diversification, much like organismal development, progresses through stages. Each stage is governed by a unique process, such that diversification within families during the Mesozoic-Cenozoic is sequentially governed by interspecific competition, non-equilibrium dynamics, temperature-dependence, and finally mass extinction. Minor deviations from these stages has led to the biodiversity we observe today. In diatoms, we show a different story of diversification, wherein conditions conducive to diatoms (e.g., cold temperatures, low prey diversity, and silica-rich oceans) lead to global abundance, which inhibits speciation. This may have particular relevance to ecological and climate change models, which generally assume that abundance promotes diversification. I discuss the significance of these results for our general understanding of the evolution and ecological distribution of species.