Diversity-dependence and the role of competition in clade diversification

Through the scope of this dissertation, I discuss the implications of diversity-dependent diversification, both as a phenomenological and a mechanistic model. Each of the following research chapters address an aspect of diversity-dependent diversification, in turn tackling its detectability in molecular phylogenies (Chapter 2), modelling the ecological processes that are hypothesized to lead to it (Chapter 3), and challenging a central assumption of the model and exploring how it impacts inference (Chapter 4). Finally, I summarise the findings of these three chapters and discuss their implications for the field of macroevolution (Chapter 5), particularly in regard to recent developments that arose during the course of the PhD.
In Chapter 2, I focus on characterizing differences between diversity-dependence and time-dependence and develop a method to reliably infer which better explains the distribution of branches in molecular phylogenies.
In Chapter 3, I depart from the phenomenological view and study an individual-based model, where trait-mediated interactions between organisms and their environment drive an adaptive radiation in a finite ecological niche space. As the radiation proceeds, niche space fills up and speciation becomes much less frequent, a process that is in line with the ecological interpretation of diversity-dependence.
In Chapter 4, I extend the individual-based model used through Chapter 2 to consider the case of multiple clades evolving in a common niche space. The ecological scenario then approximates diversification on islands.
Through these approaches, I hope to bring a better understanding of this major diversification process and more generally, how ecological dynamics influence macroevolution.