Species selection and the spatial distribution of diversity

This thesis is about Life and how it is unevenly distributed across time, space and hierarchical levels. When comparing the fossil record with the current diversity of life, the extent of the change in composition of flora and fauna over time is enormous, where some groups reigned in the past but have only few delegates surviving to the present. Spatial variation in the number of organisms is also astonishing, with the exuberance of jungles contrasting with plain arid ecosystems, one of many gradients of diversity. With a more detailed examination, one can also find examples of groups of animals or plants which have tremendously flourished producing endless forms while other groups have no more than a handful of members. In this thesis, I developed methods based on simulations and likelihood calculations. They include predictive theoretical models, and methods that are applied to case studies varying in taxonomic scope (songbirds; fish) and geographic scale (worldwide elevational distribution; lake depth gradient). I show how the spatial distribution of species is dynamic over time and has important consequences for patterns of species origination and extinction. I show that species do not have the same rates of diversification, and this can be the result of 1) regional equilibrium or out-of-equilibrium dynamics or 2) spatial distribution across gradients.