Speciation across life and the origins of biodiversity patterns

Abstract

Speciation is the original source of all species richness. Here, I address two questions: (1) what might typical speciation look like across life? and (2) how has speciation led to the diversity of life we see today? What is "typical" depends on the richness of different groups. In groups associated with host organisms (which may dominate numerically), the processes of co-speciation and host switching are crucial. Among free-living organisms, allopatric speciation, ecological divergence, and prezygotic isolation appear widely important. Yet, the processes by which species become allopatric (and initially split) remain highly unclear. Among macroscopic organisms, the processes underlying the speciation of cryptic insect lineages may predominate, and are briefly reviewed here. Analyses of diversification rates among clades can illuminate the factors that drive speciation and species richness, and I review the advantages and disadvantages, of different methods for estimating diversification rates. Patterns of species richness among named clades are generally related to variation in diversification rates, and specific types of ecological variables seem to underlie variation in diversification rates at different scales. Nevertheless, many richness patterns are unrelated to diversification rates and may be related to the time available for speciation instead, including richness among regions, clades, and traits.